Exogenous sphingomyelinase causes impaired intestinal epithelial barrier function

AIM: To test the hypothesis that hydrolysis of sphingomyelin to ceramide changes the composition of tight junctions (TJs) with increasing permeability of the intestinal epithelium. METHODS: Monolayers of Caco-2 cells were used as an in vitro model for the intestinal barrier. Permeability was determined by quantifi cation of transepithelialflux and transepithelial resistance. Sphingolipid-rich membrane microdomains were isolated by a discontinuous sucrose gradient and characterized by Western-blot. Lipid content of microdomains was analysed by tandem mass spectrometry. Ceramide was subcellularly localized by immunofluorescent staining.RESULTS: Exogenous sphingomyelinase increased transepithelial permeability and decreased transepithelial resistance at concentrations as low as 0.01 U/mL. Lipid analysis showed rapid accumulation of ceramide in the membrane fractions containing occludin and claudin-4, representing TJs. In these fractions we observed a concomitant decrease of sphingomyelin and cholesterol with increasing concentrations of ceramide. Immunofluorescent staining confirmed clustering of ceramide at the sites of cell-cell contacts. Neutralization of surface ceramide prevented the permeability-increase induced by platelet activating factor. CONCLUSION: Our findings indicate that changes in lipid composition of TJs impair epithelial barrier functions. Generation of ceramide by sphingomyelinases might contribute to disturbed barrier function seen in diseases such as inflammatory, infectious, toxic or radiogenic bowel disease.

Transforming growth factor-β1 induces intestinal myofibroblast differentiation and modulates their migration

AIM： To investigate the effects of transforming growth factor β1 （TGF-β1） on the differentiation of colonic lamina propria fibroblasts （CLPF） into myofibroblasts in vitro.METHODS： Primary CLPF cultures were incubated with TGF-β1 and analyzed for production of m-smooth muscle actin （α-SMA）, fibronectin （FN） and FN isoforms. Migration assays were performed in a modified 48-well Boyden chamber. Levels of total and phosphorylated focal adhesion kinase （FAK） in CLPF were analyzed after induction of migration.did not change α-SMA levels, while TGF-β1 treatment for 6 d significantly increased α-SIVlA production. Short term incubation （6 h） with TGF-β1 enhanced CLPF migration, while long term treatment （6 d） of CLPF with TGF-β1 reduced migration to 15%-37% compared to untreated cells. FN and FN isoform mRNA expression were increased after short term incubation with TGF-β1 （2 d） in contrast to long term incubation with TGF-β1 for 6 d. After induction of migration, TGF-β1-preincubated CLPF showed higher amounts of FN and its isoforms and lower levels of total and phosphorylated FAK than untreated cells.CONCLUSION： Long term incubation of CLPF with TGF-β1 induced differentiation into myofibroblasts with enhanced α-SMA, reduced migratory potential and FAK phosphorylation, and increased FN production. In contrast, short term contact （6 h） of fibroblasts with TGF-β1 induced a dose-dependent increase of cell migration and FAK phosphorylation without induction of α-SMA production.

Ephrin-B2 is differentially expressed in the intestinal epithelium in Crohn's disease and contributes to accelerated epithelial wound healing in vitro

AIM:Eph receptor tyrosine kinases and their membrane bound receptor-like ligands, the ephrins, represent a bi-directional cell-cell contact signaling system that directs epithelial movements in development. The meaning of this system in the adult human gut is unknown. We investigated the Eph/ephrin mRNA expression in the intestinal epithelium of healthy controls and patients with inflammatory bowel disease (IBD). METHODS: mRNA expression profiles of all Eph/ephrin family members in normal small intestine and colon were established by real-time RT-PCR. In addition, differential expression in IBD was investigated by cDNA array technology, and validated by both real-time RT-PCR and immunohistochemistry. Potential effects of enhanced EphB/ephrin-B signaling were analyzed in an in vitro IEC-6 cell scratch wound model. RESULTS: Human adult intestinal mucosa exhibits a complex pattern of Eph receptors and ephrins. Beside the known prominent co-expression of EphA2 and ephrinAl, we found abundantly co-expressed EphB2 and ephrin-B1/2. Interestingly, cDNA array data, validated by real-time PCR and immunohistochemistry, showed upregulation of ephrin-B2 in both perilesional and lesional intestinal epithelial cells of IBD patients, suggesting a role in epithelial homeostasis. Stimulation of ephrin-B signaling in ephrin- B1/2 expressing rat IEC-6-cells with recombinant EphB1-Fc resulted in a significant dose-dependent acceleration of wound closure. Furthermore, fluorescence microscopy showed that EphB1-Fc induced coordinated migration of wound edge cells is associated with enhanced formation of lamellipodial protrusions into the wound, increased actin stress fiber assembly and production of laminin at the wound edge. CONCLUSION: EphB/ephrin-B signaling might represent a novel protective mechanism that promotes intestinal epithelial wound healing, with potential impact on epithelial restitution in IBD.

Protein tyrosine phosphatase non-receptor type 2 andinflammatory bowel disease

Genome wide association studies have associated single nucleotide polymorphisms within the gene locus encoding protein tyrosine phosphatase non-receptor type 2(PTPN2) with the onset of inflammatory bowel disease(IBD) and other inflammatory disorders. Expression of PTPN2 is enhanced in actively inflamed intestinal tissue featuring a marked up-regulation in intestinal epithelial cells. PTPN2 deficient mice suffer from severe intestinal and systemic inflammation and display aberrant innate and adaptive immune responses. In particular, PTPN2 is involved in the regulation of inflammatory signalling cascades, and critical for protecting intestinal epithelial barrier function, regulating innate and adaptive immune responses, and finally for maintaining intestinal homeostasis. On one hand, dysfunction of PTPN2 has drastic effects on innate host defence mechanisms, including increased secretion of pro-inflammatory cytokines, limited autophagosome formation in response to invading pathogens, and disruption of the intestinal epithelial barrier. On the other hand, PTPN2 function is crucial for controlling adaptive immune functions, by regulating T cell proliferation and differentiation as well as maintaining T cell tolerance. In this way, dysfunction of PTPN2 contributes to the manifestation of IBD. The aim of this review is to present an overview of recent findings on the role of PTPN2 in intestinal homeostasis and the impact of dysfunctional PTPN2 on intestinal inflammation.

Serum bile acid profiling reflects enterohepatic detoxification state and intestinal barrier function in inflammatory bowel disease

AIM： To determine free and conjugated serum bile acid （BA） levels in inflammatory bowel disease （IBD） subgroups with defined clinical manifestations. METHODS： Comprehensive serum BA profiling was performed in 358 IBD patients and 310 healthy con- trols by liquid chromatography coupled to electrospray ionization tandem mass spectrometry. RESULTS： Serum levels of hyodeoxycholic acid, the CYP3A4-mediated detoxification product of the second- ary BA lithocholic acid （LCA）, was increased significantly in Crohn＇s disease （CD） and ulcerative colitis （UC）, while most other serum BA species were decreased signifi- cantly. Total BA, total BA conjugate, and total BA glyco- conjugate levels were decreased only in CD, whereas total unconjugated BA levels were decreased only in UC. In UC patients with hepatobiliary manifestations, the conjugated primary BAs glycocholic acid, taurocholic acid, and glycochenodeoxycholic acid were as signifi- cantly increased as the secondary BAs LCA, ursodeoxy- cholic acid, and tauroursodeoxycholic acid compared to UC patients without hepatobiliary manifestations. Finally, we found that in ileocecal resected CD patients, the unconjugated primary BAs, cholic acid and chenode- oxycholic acid, were increased significantly compared to controls and patients without surgical interventions. CONCLUSION： Serum BA profiling in IBD patients that indicates impaired intestinal barrier function and increased detoxification is suitable for advanced diag- nostic characterization and differentiation of IBD sub- groups with defined clinical manifestations.

Mucosal healing and deep remission: What does it mean?

The use of specific terms under different meanings and varying definitions has always been a source of confusion in science.When we point our efforts towards an evidence based medicine for inflammatory bowel diseases(IBD)the same is true:Terms such as"mucosal healing"or"deep remission"as endpoints in clinical trials or treatment goals in daily patient care may contribute to misconceptions if meanings change over time or definitions are altered.It appears to be useful to first have a look at the development of terms and their definitions,to assess their intrinsic and context-independent problems and then to analyze the different relevance in present-day clinical studies and trials.The purpose of such an attempt would be to gain clearer insights into the true impact of the clinical findings behind the terms.It may also lead to a better defined use of those terms for future studies.The terms"mucosal healing"and"deep remission"have been introduced in recent years as new therapeutic targets in the treatment of IBD patients.Several clinical trials,cohort studies or inception cohorts provided data that the long term disease course is better,when mucosal healing is achieved.However,it is still unclear whether continued or increased therapeutic measures will aid or improve mucosal healing for patients in clinical remission.Clinical trials are under way to answer this question.Attention should be paid to clearly address what levels of IBD activity are looked at.In the present review article authors aim to summarize the current evidence available on mucosal healing and deep remission and try to highlight their value and position in the everyday decision making for gastroenterologists.

Use of thiopurines in inflammatory bowel disease

The use of thiopurines as immunosuppression for the treatment of refractory or chronic active inflammatory bowel disease is established for both Crohn's disease and ulcerative colitis.Nevertheless,many questions remain concerning the optimal treatment regimens of azathioprine,6-mercaptopurine and thioguanine.We will briefly summarize dose recommendations,indications for thiopurine therapy and side effects which are relevant in clinical practice.We discuss some currently debated topics,including the combination of azathioprine and allopurinol,switching of thiopurine therapy in case of side effects,the use of azathioprine in pregnancy,the infection risk using thiopurines and the evidence when to stop thiopurines.Excellent reviews have been published on the thiopurine metabolic pathway which will not be discussed here in detail.

Pathophysiology of fistula formation in Crohn's disease

Fistulae represent an important complication in patient suffering from Crohn's disease(CD). Cumulative incidence of fistula formation in CD patients is 17%-50% and about one third of patients suffer from recurring fistulae formation. Medical treatment options often fail and also surgery frequently is not successful. Available data indicate that CD-associated fistulae originate from an epithelial defect that may be caused by ongoing inflammation. Having undergone epithelial to mesenchymal transition(EMT), intestinal epithelial cells(IEC) penetrate into deeper layers of the mucosa and the gut wall causing localized tissue damage formation of a tube like structure and finally a connection to other organs or the body surface. EMT of IEC may be initially aimed toimprove wound repair mechanisms since "conventional" wound healing mechanisms, such as migration of fibroblasts, are impaired in CD patients. EMT also enhances activation of matrix remodelling enzymes such as matrix metalloproteinase(MMP)-3 and MMP-9 causing further tissue damage and inflammation. Finally, soluble mediators like TNF and interleukin-13 further induce their own expression in an autocrine manner and enhance expression of molecules associated with cell invasiveness aggravating the process. Additionally, pathogen-associated molecular patterns also seem to play a role for induction of EMT and fistula development. Though current knowledge suggests a number of therapeutic options, new and more effective therapeutic approaches are urgently needed for patients suffering from CD-associated fistulae. A better understanding of the pathophysiology of fistula formation, however, is a prerequisite for the development of more efficacious medical anti-fistula treatments.

Role of soluble factors and three-dimensional culture in in vitro differentiation of intestinal macrophages

AIM: To examine the factor(s) involved in differentiation of intestinal macrophages (IMACs) using a recently established in vitro model. METHODS: To test whether soluble or membrane bound factors induce IMAC-differentiation, freshly elutriated monocytes (MO) were incubated with conditioned media or cell membranes of intestinal epithelial cells (IEC) or cultured with IEC in transwell systems. To determine the importance of an active migration of MO, three- dimensional aggregates from a 1:1-mixture of MO and IEC were examined by immunohistochemistry and flow cytometry. Apoptosis was examined by caspase-3 Western blots. Extracellular matrix production in differentiation models was compared by immunohistochemistry. RESULTS: IMAC differentiation was observed in a complex three-dimensional co-culture model (multicellular spheroid, MCS) with IEC after migration of MO into the spheroids. By co-culture of MO with conditioned media or membrane preparations of IEC no IMAC differentiation was induced. Co-culture of MO with IEC in transwell- cultures, with the two cell populations separated by a membrane also did not result in intestinal-like differentiation of MO. In contrast to IEC-spheroids with immigrating MO in mixed MCS of IEC and MO only a small subpopulation of MO was able to survive the seven day culture period. CONCLUSION: Intestinal-like differentiation of MO in vitro is only induced in the complex three-dimensional MCS model after immigration of MO indicating a roleof cell-matrix and/or cell-cell interactions during the differentiation of IMACs.

Perianal fistulodesis–A pilot study of a novel minimally invasive surgical and medical approach for closure of perianal fistulae

BACKGROUND Perianal fistulae strongly impact on quality of life of affected patients.AIM To challenge and novel minimally invasive treatment options are needed.METHODS Patients with Crohn’s disease(CD)in remission and patients without inflammatory bowel disease(non-IBD patients)were treated with fistulodesis,a method including curettage of fistula tract,flushing with acetylcysteine and doxycycline,Z-suture of the inner fistula opening,fibrin glue instillation,and Zsuture of the outer fistula opening followed by post-operative antibiotic prophylaxis with ciprofloxacin and metronidazole for two weeks.Patients with a maximum of 2 fistula openings and no clinical or endosonographic signs of a complicated fistula were included.The primary end point was fistula healing,defined as macroscopic and clinical fistula closure and lack of patient reported fistula symptoms at 24 wk.RESULTS Fistulodesis was performed in 17 non-IBD and 3 CD patients,with a total of 22 fistulae.After 24 wk,all fistulae were healed in 4 non-IBD and 2 CD patients(overall 30%)and fistula remained closed until the end of follow-up at 10-25 mo.In a secondary per-fistula analysis,7 out of 22 fistulae(32%)were closed.Perianal disease activity index(PDAI)improved in patients with fistula healing.Low PDAI was associated with favorable outcome(P=0.0013).No serious adverse events were observed.CONCLUSION Fistulodesis is feasible and safe for perianal fistula closure.Overall success rates is at 30%comparable to other similar techniques.A trend for better outcomes in patients with low PDAI needs to be confirmed.