Ulcerative Colitis: Fromm M

Schulzke JD, Ploeger S, Amasheh M, Fromm A, Zeissig S, Troeger H, Richter J, Bojarski C, Schumann M, Fromm M. · Department of General Medicine & Pathophysiology of Enteral Nutrition, Charité, Campus Benjamin Franklin, Berlin, Germany. · Ann N Y Acad Sci. · Pubmed #19538319 No free full text.

Abstract: The epithelium in inflamed intestinal segments of patients with Crohn's disease is characterized by a reduction of tight junction strands, strand breaks, and alterations of tight junction protein content and composition. In ulcerative colitis, epithelial leaks appear early due to micro-erosions resulting from upregulated epithelial apoptosis and in addition to a prominent increase of claudin-2. Th1-cytokine effects by interferon-gamma in combination with TNFalpha are important for epithelial damage in Crohn's disease, while interleukin-13 (IL-13) is the key effector cytokine in ulcerative colitis stimulating apoptosis and upregulation of claudin-2 expression. Focal lesions caused by apoptotic epithelial cells contribute to barrier disturbance in IBD by their own conductivity and by confluence toward apoptotic foci or erosions. Another type of intestinal barrier defect can arise from alpha-hemolysin harboring E. coli strains among the physiological flora, which can gain pathologic relevance in combination with proinflammatory cytokines under inflammatory conditions. On the other hand, intestinal barrier impairment can also result from transcellular antigen translocation via an initial endocytotic uptake into early endosomes, and this is intensified by proinflammatory cytokines as interferon-gamma and may thus play a relevant role in the onset of IBD. Taken together, barrier defects contribute to diarrhea by a leak flux mechanism (e.g., in IBD) and can cause mucosal inflammation by luminal antigen uptake. Immune regulation of epithelial functions by cytokines may cause barrier dysfunction not only by tight junction impairments but also by apoptotic leaks, transcytotic mechanisms, and mucosal gross lesions.

Kroesen AJ, Dullat S, Schulzke JD, Fromm M, Buhr HJ. · Department of Surgery, Charité-Universitatsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany. · Scand J Gastroenterol. · Pubmed #18569988 No free full text.

Abstract: OBJECTIVE: Backwash ileitis (BI) has not been identified as a risk factor for pouchitis. The aim of this study was to investigate the barrier function of the ileoanal pouch depending on the presence of BI. The incidence of pouchitis in a population of ulcerative colitis patients with BI is also reported. MATERIAL AND METHODS: Biopsies were taken from 80 patients with ulcerative colitis: a) terminal ileum prior to pouch creation (pre-IAP); b) 16 months after ileostomy closure (intact pouch); and c) during pouchitis. Patients were stratified into the BI group and the non-BI (ØBI) group. Barrier function was determined in Ussing-chambers as epithelial resistance by impedance analysis and as mannitol permeability from (3)H-mannitol fluxes. Na(+)-glucose co-transport was measured as a change in short-circuit current (I(SC)) after addition of glucose. Relative risk of developing pouchitis was calculated by corrected chi(2) test. RESULTS: In 13/21 (BI/ØBI) pre-IAP patients, 23/37 (BI/ØBI) with an intact pouch, and 35/7 (BI/ØBI) with pouchitis, epithelial resistance in BI/ØBI was 13.5+/-1.6/14.3+/-0.9 Omega.cm(2) for pre-IAP, 12.7+/-1.3/16.8+/-1.2 Omega x cm(2) (p<0.05 BI versus ØBI) for the intact pouch, and 10.1+/-1.1/9.9+/-1.8 Omega x cm(2) for pouchitis (p<0.05 BI versus ØBI with an intact pouch). No differences were found for electrogenic chloride secretion and active Na(+)-glucose co-transport between BI/ØBI in the three groups. In patients with BI, pouchitis was more common (35 versus 7 patients, odds ratio 33.0 (95% CI 8.3-143.9; p<0.0001)). CONCLUSIONS: Ulcerative colitis patients with BI show impaired barrier function in the further course of the ileoanal pouch. Thus, BI has a long-term impact on epithelial barrier function.

Schulzke JD, Bojarski C, Zeissig S, Heller F, Gitter AH, Fromm M. · Medizinische Klinik I, Department of Gastroenterology, Infectious Diseases and Rheumatology, Charité, Campus Benjamin Franklin, 12200 Berlin, Germany. · Ann N Y Acad Sci. · Pubmed #17057208 No free full text.

Abstract: Epithelial barrier function is determined by trans- and paracellular permeabilities, the latter of which is mainly influenced by tight junctions (TJs) and apoptotic leaks within the epithelium. The present article aims to present experimental evidence for a functional role of epithelial apoptoses by means of cell culture models as well as in tissues from patients with inflammatory bowel disease. It is shown that epithelial apoptoses are sites of elevated conductance within the intestinal epithelium and that proinflammatory cytokines like TNF-alpha upregulate both the apoptotic rate and single apoptotic conductivity, making cytokine-induced apoptosis functionally far more relevant than is spontaneous apoptosis. In ulcerative colitis and Crohn's disease (CD), but not in collagenous colitis, apoptotic rates are increased to about 5%, in mild-to-moderately inflamed colon specimens, where as the control apoptotic rate is about 2%. Thus, epithelial apoptoses lead to a loss of ions and water into the intestinal lumen, causing leak flux diarrhea and enabling small antigens of <4,000 Da in the intestinal lumen to enter the intestinal mucosa, thereby perpetuating inflammatory responses. In addition to TNF-alpha, interleukin (IL)-13 is an important inductor of epithelial apoptosis in Th2 immune responses. Therapeutically,TNF-alpha-antibodies (infliximab) can restore barrier function in Crohn's disease by downregulating epithelial apoptoses, while epithelial TJs are unaffected.

Kroesen AJ, Leistenschneider P, Lehmann K, Ransco C, Dullat S, Blaut M, Schulzke JD, Fromm M, Buhr HJ. · Department of Surgery, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany. · Inflamm Bowel Dis. · Pubmed #16917229 No free full text.

Abstract: BACKGROUND AND AIMS: Bacterial overgrowth appears to play an important role in the pathogenesis of ileoanal pouches. Therefore, the capability of bacterial permeation and its determinants is of great interest. The aim of this study was to examine bacterial permeation in the ileoanal pouch and to correlate the results with the degree of inflammation, the epithelial resistance, the mucosal transport function, and the age of the ileoanal pouches. MATERIALS AND METHODS: Biopsies were taken from 54 patients before colectomy (n = 13; preileal pouch-anal anastomosis [IPAA]), and closure of ileostomy (n = 7; deviation), <1 year after closure of ileostomy (n = 8; intact pouch I), >1 year after closure of ileostomy (n = 16; intact pouch II), in the case of pouchitis (n = 11), and in 11 controls. Tissues were mounted in a miniaturized Ussing chamber. Escherichia coli was added to the mucosal side of the Ussing chamber, and the permeation was proven by serosal presence of E. coli. Epithelial and subepithelial resistance was determined by transmural impedance analysis. Active Na-glucose cotransport and active Cl secretion were measured. Specimens were analyzed by fluorescent in situ hybridization with oligonucleotide probes targeting the bacterial 16s ribosomal RNA. The bacteria in and on the tissue were enumerated. RESULTS: Bacterial permeation occurred in 2 of 13 pre-IPAA, 2 of 7 deviations, 0 of 8 intact pouch I, 9 of 16 intact pouch II, 5 of 11 pouchitis specimens, and 0 of 11 ileum controls. The frequency of bacterial permeation in the intact pouch II group is higher than in the intact pouch I group (P < 0.001). Epithelial resistance, mannitol fluxes, electrogenic chloride secretion, sodium-glucose cotransport of the bacterially permeated specimens versus nonpermeated of the intact pouch II group, and the pouchitis group and subepithelial resistance remained unchanged. Intramural bacteria could be detected by fluorescence in situ hybridization mainly in long-lasting pouches, but there was no correlation with bacterial permeation. CONCLUSIONS: The long-lasting ileoanal pouch is associated with increased bacterial permeability. This is not correlated with a disturbed function of the pouch mucosa but could be a precursor of pouchitis.

Zeissig S, Bürgel N, Günzel D, Richter J, Mankertz J, Wahnschaffe U, Kroesen AJ, Zeitz M, Fromm M, Schulzke JD. · Department of Gastroenterology, Charité, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany. · Gut. · Pubmed #16822808 No free full text.

Abstract: BACKGROUND: Epithelial barrier function is impaired in Crohn's disease. AIM: To define the underlying cellular mechanisms with special attention to tight junctions. METHODS: Biopsy specimens from the sigmoid colon of patients with mild to moderately active or inactive Crohn's disease were studied in Ussing chambers, and barrier function was determined by impedance analysis and conductance scanning. Tight junction structure was analysed by freeze fracture electron microscopy, and tight junction proteins were investigated immunohistochemically by confocal laser scanning microscopy and quantified in immunoblots. Epithelial apoptosis was analysed in terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling and 4',6-diamidino-2-phenylindole staining. RESULTS: Patients with active Crohn's disease showed an impaired intestinal barrier function as indicated by a distinct reduction in epithelial resistance. As distribution of conductivity was even, focal epithelial lesions (eg, microerosions) did not contribute to barrier dysfunction. Instead, freeze fracture electron microscopy analysis showed reduced and discontinuous tight junction strands. Occludin and the sealing tight junction proteins claudin 5 and claudin 8 were downregulated and redistributed off the tight junction, whereas the pore-forming tight junctions protein claudin 2 was strongly upregulated, which constitute the molecular basis of tight junction changes. Other claudins were unchanged (claudins 1, 4 and 7) or not detectable in sigmoid colon (claudins 11, 12, 14, 15 and 16). Claudin 2 upregulation was less pronounced in active Crohn's disease compared with active ulcerative colitis and was inducible by tumour necrosis factor alpha. As a second source of impaired barrier function, epithelial apoptosis was distinctly increased in active Crohn's disease (mean (SD) 5.2 (0.5)% v 1.9 (0.2)% in control). By contrast, barrier function, tight junction proteins and apoptosis were unaffected in Crohn's disease in remission. CONCLUSION: Upregulation of pore-forming claudin 2 and downregulation and redistribution of sealing claudins 5 and 8 lead to altered tight junction structure and pronounced barrier dysfunction already in mild to moderately active Crohn's disease.

Heller F, Florian P, Bojarski C, Richter J, Christ M, Hillenbrand B, Mankertz J, Gitter AH, Bürgel N, Fromm M, Zeitz M, Fuss I, Strober W, Schulzke JD. · Department of Gastroenterology, Charité, Campus Benjamin Franklin, Berlin, Germany. · Gastroenterology. · Pubmed #16083712 No free full text.

Abstract: BACKGROUND & AIMS: Ulcerative colitis (UC) is characterized by a Th2 immune response with inflammation and epithelial barrier dysfunction. So far, Th2 cytokines have not been shown to directly influence epithelial barrier function. METHODS: Lamina propria mononuclear cells (LPMCs) were stimulated and interleukin (IL)-13 was measured by enzyme-linked immunosorbent assay. Functional IL-13 and IL-4 effects were studied on HT-29/B6 colonic epithelial cells in Ussing chambers and by conductance scanning. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays. IL-13/IL-4 receptors were analyzed by reverse-transcription polymerase chain reaction and immunofluorescence. Western blotting combined with immunofluorescence was used to detect tight junction proteins. Furthermore, restitution velocity was measured. Finally, mucosal biopsy specimens from patients with UC were compared with cultured cells for these features. RESULTS: LPMCs from patients with UC produced large amounts of IL-13 (985 +/- 73 pg/mL), much more than from controls or patients with Crohn's disease. IL-13Ralpha1 and IL-4Ralpha receptors were present in HT-29/B6 cells and colonic epithelial cells of control patients and patients with UC. IL-13 had a dose-dependent effect on transepithelial resistance of HT-29/B6 monolayers (reduction to 60% +/- 4%), whereas IL-4 had no effect. This was due to an increased number of apoptotic cells (5.6-fold +/- 0.9-fold) and an increased expression of the pore-forming tight junction protein claudin-2 to 295% +/- 37%, both of which contributed equally. Finally, epithelial restitution velocity decreased from 15.1 +/- 0.6 to 10.6 +/- 0.5 microm/h after treatment with IL-13. Parallel changes were observed in human samples, with an increase in claudin-2 expression to 956% +/- 252%. CONCLUSIONS: IL-13 was identified as an important effector cytokine in UC that impairs epithelial barrier function by affecting epithelial apoptosis, tight junctions, and restitution velocity.

Amasheh S, Barmeyer C, Koch CS, Tavalali S, Mankertz J, Epple HJ, Gehring MM, Florian P, Kroesen AJ, Zeitz M, Fromm M, Schulzke JD. · Department of Clinical Physiology, Campus Benjamin Franklin, Charité-University Medicine Berlin, Hindenburgdamm 30, 12200 Berlin, Germany. · Gastroenterology. · Pubmed #15188166 No free full text.

Abstract: BACKGROUND & AIMS: The main limiting factor for sodium absorption in distal colon is the amiloride-sensitive epithelial sodium channel (ENaC). This study aimed to characterize mechanisms involved in the dysregulation of ENaC expression in ulcerative colitis (UC). METHODS: Epithelial preparations from surgically removed inflamed and control sigmoid colons were used. Active electrogenic Na(+) transport (J(Na)) was determined after 8-hour aldosterone stimulation in Ussing-chambers (corrected for the altered epithelial/subepithelial resistance ratio). Subsequently, ENaC alpha-, beta-, and gamma-subunits were analyzed immunohistochemically and in Western and Northern blots (corrected for the inflammatory increase in subepithelial protein content). To study gene regulation, the promoters of beta- and gamma-ENaC were analyzed in reporter gene assays. RESULTS: In controls, aldosterone stimulated J(Na) and induced ENaC beta- and gamma-subunit expression, whereas this response was virtually abolished in UC. Preservation of surface epithelium in UC was indicated by unchanged ENaC alpha-subunit expression, which points also against a mere immaturity or epithelial cell loss. Inhibition of electrogenic sodium transport as well as beta- and gamma-ENaC mRNA expression could be mimicked in control colon by in vitro preexposure for 8 hours to tumor necrosis factor alpha and interferon gamma. Promoter analysis revealed that down-regulation of beta- and gamma-ENaC gene expression was primarily induced by tumor necrosis factor alpha. CONCLUSIONS: We conclude that, in UC, elevated proinflammatory cytokines selectively impair beta- and gamma-ENaC expression, which contributes to diarrhea by reducing colonic sodium absorption.

Barmeyer C, Harren M, Schmitz H, Heinzel-Pleines U, Mankertz J, Seidler U, Horak I, Wiedenmann B, Fromm M, Schulzke JD. · Department of Gastroenterology, Charité-University Medicine Berlin, 12200 Berlin, Germany. · Am J Physiol Gastrointest Liver Physiol. · Pubmed #14715519 links to  free full text

Abstract: Colitis in interleukin-2-deficient (IL-2(-/-)) mice resembles ulcerative colitis in humans. We studied epithelial transport and barrier function in IL-2(-/-) mice and used this model to characterize mechanisms of diarrhea during intestinal inflammation. (22)Na(+) and (36)Cl(-) fluxes were measured in proximal colon. Net Na(+) flux was reduced from 4.0 +/- 0.5 to 0.8 +/- 0.5 micromol.h(-1).cm(-2), which was paralleled by diminished mRNA and protein expression of the Na(+)/H(+) exchanger NHE3. Net Cl(-) flux was also decreased from 2.2 +/- 1.6 to -2.7 +/- 0.6 micromol.h(-1).cm(-2), indicating impaired Na(+)-Cl(-) absorption. In distal colon, aldosterone-induced electrogenic Na(+) absorption was 6.1 +/- 0.9 micromol.h(-1).cm(-2) in controls and was abolished in IL-2(-/-) mice. Concomitantly, mRNA expression of beta- and gamma-subunits of the epithelial sodium channel (ENaC) was reduced. Epithelial barrier was studied in proximal colon by impedance technique and mannitol fluxes. In contrast to ulcerative colitis, epithelial resistance was increased and mannitol fluxes were decreased in IL-2(-/-) mice. This was in accord with the findings of reduced ion transport as well as increased expression of tight junction proteins occludin and claudin-1, -2, -3, and -5. In conclusion, the IL-2(-/-) mucosa exhibits impaired electroneutral Na(+)-Cl(-) absorption and electrogenic Na(+) transport due to reduced mRNA and protein expression of NHE3 and ENaC beta- and gamma-subunit mRNA. This represents a model of early intestinal inflammation with absorptive dysfunction due to impaired transport protein expression/function while epithelial barrier is still intact. Therefore, this model is ideal to study regulation of transporter expression independent of barrier defects.

Barmeyer C, Horak I, Zeitz M, Fromm M, Schulzke JD. · Medical Clinic I - Gastroenterology, Infectious Diseases and Rheumatology, University Clinic Benjamin Franklin, Free University of Berlin, Berlin, Germany. · Pathobiology. · Pubmed #12571417 No free full text.

Abstract: Interleukin-2-deficient (IL-2(-/-)) mice develop colitis with striking clinical and morphological similarities to ulcerative colitis. Since transport and barrier properties are impaired in ulcerative colitis, we studied transport and barrier functions in IL-2(-/-) mice in order to gain insight for the first time into the general pathomechanisms of disturbed transport and barrier function of the intestine during inflammation. Alternating current impedance analysis was used to determine tissue conductance in the inflamed proximal colon of IL-2(-/-) mice and to discriminate between pure epithelial and subepithelial conductance. Surprisingly, epithelial conductance was not increased but diminished in IL-2(-/-) mice compared to controls (20.2 +/- 1.3 versus 28.8 +/- 2.8 mS/cm(2)). Concomitantly, conductance of the subepithelial tissue layers was decreased in IL-2(-/-) mice as a result of edema and infiltration with inflammatory cells. In the distal colon, electrogenic Na(+) transport (J(Na)) mediated by the epithelial Na(+) channel (ENaC) was measured 8 h after stimulation with 3.10(-9) M aldosterone in vitro as the drop in I(SC) (short circuit current) after addition of 10(-4) M amiloride. In controls, J(Na) was 6.9 +/- 0.9 micromol x h(-1) x cm(-2), whereas it was abolished in IL-2(-/-) mice. In conclusion, the inflamed colon of IL-2(-/-) mice exhibits a severe disturbance in Na(+) uptake via the ENaC in the absence of a barrier defect. Thus, reduced expression of active absorptive transport and not a barrier defect is responsible for the diarrhea in this model of intestinal inflammation. This makes this model suitable for studying the general pathomechanisms of the inflammatory downregulation of intestinal transport proteins.

Kroesen AJ, Stockmann M, Ransco C, Schulzke JD, Fromm M, Buhr HJ. · Department of Surgery, University Hospital Benjamin Franklin, Freie Universität Berlin, Germany. · Gut. · Pubmed #12010884 links to  free full text

Abstract: BACKGROUND AND AIMS: Little is known of the permeability of ileoanal pouches. Hence the aim of the present study was to determine changes in permeability and mucosal function after ileo-pouchanal anastomosis (IPAA) in patients with ulcerative colitis. MATERIALS AND METHODS: Biopsies were taken from 43 patients (male:female ratio 28:15; mean age 35.2 (12.5) years) prior to colectomy (ileum prior to pouch), prior to closure of ileostomy (deviation), and after closure of ileostomy (intact pouch) in the case of pouchitis, and from 14 healthy controls. Tissues were mounted in a miniaturised Ussing chamber. Epithelial and subepithelial resistance was determined by transmural impedance analysis. Active Na(+)-glucose cotransport was measured as change in short circuit current after stepwise addition of glucose, and active Cl(-) secretion was measured after stimulation with theophylline and prostaglandin E(2). RESULTS: Neither epithelial resistance nor mannitol fluxes were significantly altered compared with intact controls, indicating no barrier defect in pouchitis. Subepithelial resistances of intact pouches and pouchitis were increased compared with deviation (18.2 (1.6) and 24.3 (1.5) v. 13.6 (1.0) Omegaxcm(2)) consistent with an adaptive thickening of the subepithelial layer. In contrast, active Cl(-) secretion of pouchitis tissues was reduced versus intact pouch and controls (1.4 (0.3) v. 4.3 (0.7) and 4.6 (0.7) micromol/h/cm(2)), and Na(+)-glucose cotransport of pouchitis was reduced compared with intact pouch and controls (1.8 (0.5) v. 4.2 (0.8) and 8.8 (1.3) micromol/h/cm(2)). CONCLUSIONS: Ileal mucosa in pouchitis and terminal ileum prior to IPAA exhibit impaired secretory and absorptive transport functions whereas the epithelial barrier function remains unchanged. This differs from findings in ulcerative colitis. Thus the hypothesis that pouchitis represents a remanifestation of ulcerative colitis has to be questioned.

Gitter AH, Wullstein F, Fromm M, Schulzke JD. · Institut für Klinische Physiologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, 12200 Berlin, Germany. · Gastroenterology. · Pubmed #11729111 No free full text.

Abstract: BACKGROUND & AIMS: In ulcerative colitis (UC), the epithelial barrier is impaired by erosion/ulcer-type lesions and epithelial apoptosis causing local leaks, and generalized tight junction alterations increasing the basal permeability. We quantified the contribution of these mechanisms to the increased colonic ion permeability. METHODS: Sigmoid colon was stripped, and the spatial distribution of current clamped across the viable epithelium was recorded by a microelectrode probe, using the conductance scanning method. Local leaks (circumscribed conductive peaks) were marked, and structural changes were studied in H&E-stained series sections. RESULTS: Overall conductivity increased from 8.4 +/- 0.7 mS/cm(2) (mean +/- SEM) in controls to 11.7 +/- 0.6 in specimens with mild inflammation (i.e., with intact epithelium) and 34.4 +/- 6.2 mS/cm(2) in moderate-to-severe inflammation (i.e., with visible epithelial lesions). Only in part this was caused by a generalized increase in basal conductivity (12.2 +/- 1.5 mS/cm(2) in moderate-to-severe UC vs. 8.3 +/- 0.7 in controls). More importantly, the spatial distribution of conductivity, which was even in controls, showed dramatic leaks in UC. Leaks found in mild inflammation without epithelial lesion turned out to be foci of epithelial apoptosis. In moderate-to-severe inflammation, leaks correlated with epithelial erosion/ulcer-type lesions or crypt abscesses. CONCLUSIONS: In early UC, but not in controls, seemingly intact epithelium comprises leaks at apoptotic foci. With more intensive inflammation, erosion/ulcer-type lesions are highly conductive, even if covered with fibrin. Local leaks contribute 19% to the overall epithelial conductivity in mild and 65% in moderate-to-severe inflammation.

Schmitz H, Barmeyer C, Gitter AH, Wullstein F, Bentzel CJ, Fromm M, Riecken EO, Schulzke JD. · Medizinische Klinik I, Gastroenterologie und Infektiologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, 12200 Berlin, Germany. · Ann N Y Acad Sci. · Pubmed #11193594 No free full text.

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Schmitz H, Barmeyer C, Fromm M, Runkel N, Foss HD, Bentzel CJ, Riecken EO, Schulzke JD. · Department of Gastroenterology, Universitätsklinikum Benjamin Franklin, Freie Universität, Berlin, Germany. · Gastroenterology. · Pubmed #9922310 No free full text.

Abstract: BACKGROUND & AIMS: Mechanisms of diarrhea in ulcerative colitis (UC) are still unknown. Functional and structural characterization of epithelial barrier and transport properties in ulcerative colitis (UC) was performed. METHODS: Inflamed sigmoid colon epithelium from UC patients was studied by alternating current impedance analysis to determine the pure epithelial resistance as a measure of intestinal barrier function. Tight junction (TJ) structure was investigated by freeze-fracture electron microscopy. RESULTS: Although total wall resistance was reduced in UC by 50%, impedance analysis uncovered a much more pronounced barrier defect. Epithelial resistance decreased from 95 +/- 5 to 20 +/- 3 omega3. cm2, which in conventional analysis is masked by an increase in subepithelial resistance from 14 +/- 1 to 36 +/- 3 omega3. cm2 caused by inflammation. This was paralleled by a change in epithelial cell TJ structure in UC. Strand count decreased from 6.94 +/- 0.25 to 4.76 +/- 0.47 at the surface and from 7.26 +/- 0.31 to 5.46 +/- 0.37 in the crypts. Conclusions: The inflamed colonic mucosa in UC has an impaired barrier function that is much more pronounced than previously assumed. An altered TJ structure contributes to this barrier defect which, because of increased back leak, can reduce net ion transport. Thus, a leak-flux mechanism contributes to the diarrhea in UC.