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Background & Aims: Crohn's disease (CD) is a chronic inflammatory bowel disease. In this study, we have investigated sodium absorption via epithelial sodium channels (ENaC) in the macroscopically noninflamed colon in active CD. Methods: Sodium transport via ENaC was investigated in Ussing chambers using biopsy specimens of sigmoid colon from controls and active CD limited to the small intestine. ENaC messenger RNA expression and subcellular localization were studied by real-time polymerase chain reaction and confocal microscopy. Effects of proinflammatory cytokines on ENaC and signaling via mitogen-activated protein kinases were investigated in rat distal colon. Therapeutic inhibition of mitogen-activated protein kinases was studied in CD biopsy specimens. Results: Electrogenic sodium absorption via ENaC was strongly impaired in the macroscopically noninflamed CD colon because of reduced γ-ENaC transcription, whereas subcellular localization of ENaC was not changed. In contrast to impaired epithelial sodium transport, epithelial barrier function was not altered in noninflamed CD colon, indicating that paracellular leak flux of ions did not contribute to decreased sodium absorption. Exposure of rat distal colon to tumor necrosis factor α led to reduced electrogenic sodium absorption because of impaired transcriptional γ-ENaC induction, which resembled the changes found in CD. Tumor necrosis factor α effects were dependent on extracellular signal-regulated kinase 1/2 but not p38 or c-Jun-N-terminal kinase because inhibition of mitogen-activated protein kinase/extracellular regulated kinase (MEK)1/2 but not inhibition of p38 or c-Jun-N-terminal kinase prevented suppression of ENaC. Finally, therapeutic inhibition of MEK1/2 restored electrogenic sodium absorption in CD. Conclusions: In CD, macroscopically noninflamed colon contributes to diarrhea via impaired ENaC-mediated sodium absorption. Inhibition of extracellular signal-regulated kinase might serve as a potential therapeutic strategy for CD diarrhea.

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-13Rα1 and IL-4Rα 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 μm/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.

Background & Aims: Collagenous colitis is an inflammatory disease of unknown etiology with diarrhea as the leading symptom. The aim of this study was to examine the pathogenic mechanisms of this disease. Methods: Biopsy specimens of the sigmoid colon were obtained endoscopically. Short-circuit current and 22Na and 36Cl fluxes were measured in miniaturized Ussing chambers. Alternating current impedance analysis discriminated epithelial from subepithelial resistance. Tight junction proteins occludin and claudin 1–5 were characterized in membrane fractions by Western blotting. Apoptotic ratio was determined by DAPI and TUNEL staining. Results: In collagenous colitis, net Na+ flux decreased from 8.8 ± 1.8 to 0.2 ± 1.5 and net Cl− flux from 11.2 ± 3.0 to −3.0 ± 2.7 μmol · h−1 · cm−2, indicating a pronounced decrease in NaCl absorption. The fact that short-circuit current increased from 1.5 ± 0.4 to 3.9 ± 0.8 μmol · h−1 · cm−2, together with the negative net Cl− flux, points to activation of active electrogenic chloride secretion. Subepithelial resistance increased from 7 ± 1 to 18 ± 2 Ω · cm2 due to subepithelial collagenous bands of 48 ± 8–μm thickness. Epithelial resistance was diminished from 44 ± 3 to 29 ± 2 Ω · cm2, and this was accompanied by a decrease in occludin and claudin-4 expression. Neither mucosal surface area nor apoptotic ratio was altered in collagenous colitis. Conclusions: Reduced net Na+ and Cl− absorption is the predominant diarrheal mechanism in collagenous colitis, accompanied by a secretory component of active electrogenic chloride secretion. The subepithelial collagenous band as a significant diffusion barrier is a cofactor. Down-regulation of tight junction molecules but not epithelial apoptoses is a structural correlate of barrier dysfunction contributing to diarrhea by a leak flux mechanism. GASTROENTEROLOGY 2002;123:433-443

Background: East Asian countries have historically reported low incidences of microscopic colitis and inflammatory bowel disease. (Ahuja & Tandon, J Dig Dis, 2010). However, it is unclear whether these data reflect genetic or environmental factors or are the result of different diagnostic criteria among physicians and pathologists. To address this question, we have designed a study to estimate the prevalence of these conditions among adult patients of East Asian ancestry who live in the U.S., have had colonoscopies in the U.S., and had their biopsies evaluated by a single group of U.S. gastrointestinal pathologists. Methods: From a large national pathology database of subjects who had colonoscopy with ileocolonic biopsies between 1.2008 and 8.2013 in endoscopy centers through the U.S., we extracted all adult patients identified as Korean, Chinese, Japanese, or Vietnamese (collectively referred to as East Asians). Controls were all other adults. We then recorded the histopathologic diagnoses of Crohn's Disease, Ulcerative Colitis, Lymphocytic Colitis, and Collagenous Colitis, and compared their prevalence in East Asian patients to that of controls using unadjusted odds ratios. If a patient had multiple procedures during the study period, only the first chronological procedure was selected. Results: There were 14,209 unique East Asian patients (median age 59 years; 53.2% men) and 1,254,986 unique controls (median age 60 years; 48.9% men). Figure 1 shows the relative prevalence of the four types of colitis in each group. Conclusions: In our series, patients of East Asian descent living in the U.S. were affected by microscopic colitis and inflammatory bowel disease to a much lesser extent that those of other ancestries. The two groups of patients were similar in age and sex distribution, had their endoscopic procedures in similar U.S. settings, and their histopathologic diagnoses were made by a single pathology group whose members adhere to common criteria. Therefore, the remarkably low prevalence of non-infectious colitides detected in this analysis is likely to reflect, at least in part, genetic factors. Determining the relative risk in several generations of Asians in the U.S. might help determine whether environmental factors play a significant role in the development of these conditions.

The standard treatment of IBD involves the application of anti-inflammatory drugs. These drugs become systemically bioavailable and bear a potential of strong adverse effects. Thus, targeting the inflamed areas of the intestine can reduce adverse effects. Polymeric particles have turned out to be a promising tool for the targeted delivery of drugs. We aimed to investigate the distribution of fluoresceine-labelled nanoparticles (NP) and microparticles (MP) in the rectal mucosa of patients with IBD by use of CLE. Fluoresceinaminewas covalently bound to poly(L-lactide-co-glycolide) (PLGA). From this modified polymer, nanoparticles of approximately 300 nm size and microparticles of 3.5 μm size were prepared. After bowel preparation a 30 ml enema containing 10E9 MP or 10E13 NP, resp., has been applied to patients with rectal Crohns disease (CD) or ulcerative colitis (UC). After two hours endoscope based CLE has been performed to visualize nanoparticles in areas of different stages of inflammation. Biopsies have been obtained from IBD patients to evaluate mucosal transport processes in miniaturized Ussing chambers by confocal laser endoscopy. We examined 16 patients with IBD (8 patients with CD, 10 patients with (UC), 7 of whom received NP while 9 received MP. No particles have been visualized on intact mucosal surfaces. In areas of mild to moderate inflammation only minor amounts of particles were visible. In contrast, we observed a marked accumulation of MP rather than NP in ulcerous lesions. Preliminary results from Ussing chamber experiments suggest an influx of particles into the gut mucosa through epithelial lesions. Representative images are shown in fig. 1. This is the first study demonstrating mucosal accumulation of microparticles and nanoparticles in intestinal lesions of patients with IBD. Drug containing particles may have a great potential to target these lesions more specifically in order to maximize therapeutic efficacy and minimize potential side effects. CLE is a useful tool to investigate drug delivery to mucosal surfaces.