Christian Bojarski

Downregulation of epithelial apoptosis and barrier repair in active Crohn’s disease by tumour necrosis factor α antibody treatment

Background and aims: Barrier dysfunction is an important feature contributing to inflammation and diarrhoea in Crohn’s disease (CD). Recently, tumour necrosis factor α (TNF-α) antibodies were recognised as effective in steroid refractory CD. The aim of this study was to characterise the effects of this therapy on the epithelial barrier. Patients and methods: Forceps biopsies were obtained from the sigmoid colon before and 14 days after TNF-α antibody therapy in 11 patients treated for chronic active CD (Crohn’s disease activity index >150). Epithelial apoptoses were measured after terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labelling (TUNEL) and 4′,6-diamidino-2-phenylindole staining. Epithelial resistance was determined by alternating current impedance analysis in miniaturised Ussing chambers. Occludin, claudin 1, and claudin 4 expression was quantified in immunoblots. Results: The epithelial apoptotic ratio was 2.1 (0.2)% in controls and increased to 5.3 (1.0)% in CD. TNF-α antibody therapy decreased the apoptotic ratio to 2.9 (1.0)% (normalised in 10 of 11 patients). In parallel, epithelial resistance was lower in CD than in controls (24 (3) v 42 (3) Ω×cm2) and improved to 34 (3) Ω×cm2 after therapy. Occludin, claudin 1, and claudin 4 were not affected by TNF-α antibody therapy. In support of a functional role of epithelial apoptoses in CD, a similar decrease in resistance of −40% was observed when the apoptotic rate was selectively upregulated from 2.6% to 5.4% with camptothecin in HT-29/B6 cells. Conclusions: Epithelial apoptoses were upregulated in the colon in CD and restored to normal in 10 of 11 patients by TNF-α antibody therapy. This is the structural correlate of epithelial barrier dysfunction measured as epithelial resistance while expression of tight junction proteins did not contribute to this therapeutic effect.

Epithelial Tight Junctions in Intestinal Inflammation

The epithelium in inflamed intestinal segments of patients with Crohns 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‐γ in combination with TNFα are important for epithelial damage in Crohns 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 α‐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‐γ 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.

Mechanisms of diarrhea in collagenous colitis

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 (22)Na and (36)Cl 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 micromol x h(-1) x 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 micromol x h(-1) x 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 Omega x cm(2) due to subepithelial collagenous bands of 48 +/- 8-microm thickness. Epithelial resistance was diminished from 44 +/- 3 to 29 +/- 2 Omega x cm(2), 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.

The specific fates of tight junction proteins in apoptotic epithelial cells

The polarized morphology of epithelial cells depends on the establishment and maintenance of characteristic intercellular junctions. The dramatic morphological changes observed in apoptotic epithelial cells were ascribed at least in part to the specific fragmentation of components of adherens junctions and desmosomes. Little, however, is known about tight junctions during apoptosis. We have found that after induction of apoptosis in epithelial cells, tight junction proteins undergo proteolytic cleavage in a distinctive manner correlated with a disruption of tight junctions. The transmembrane protein occludin and, likewise, the cytoplasmic adaptor proteins ZO-1 and ZO-2 are fragmented by caspase cleavage. In addition, occludin is cleaved at an extracellular site by a metalloproteinase. The caspase cleavage site in occludin was mapped C-terminally to Asp320 within the C-terminal cytoplasmic domain. Mutagenesis of this site efficiently blocked fragmentation. In the presence of caspase and/or metalloproteinase inhibitors, fragmentation of occludin, ZO-1 and ZO-2 was blocked and cellular morphology was almost fully preserved. Interestingly, two members of the claudin family of transmembrane tight junction proteins exhibited a different behavior. While the amount of claudin-2 protein was reduced similarly to occludin, ZO-1 and ZO-2, claudin-1 was either fully preserved or was even increased in apoptotic cells.

Disrupted Barrier Function through Epithelial Cell Apoptosis

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‐α 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 Crohns 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‐α, interleukin (IL)‐13 is an important inductor of epithelial apoptosis in Th2 immune responses. Therapeutically,TNF‐α‐antibodies (infliximab) can restore barrier function in Crohns disease by downregulating epithelial apoptoses, while epithelial TJs are unaffected.

Helicobacter pylori infection and chronic urticaria

Together with antihistamines, various antibiotics including penicillin, tetracycline, and others have been empirically used to treat chronic urticaria in an attempt to eliminate an underlying focal infection. On the basis of this knowledge, we posed the question as to whether Helicobacter pylori infection could be an underlying cause of chronic urticaria. H. pylori infection can easily be diagnosed with high sensitivity and specificity with the [13C]-urea breath test.l, 2 The present study was performed to investigate the possible role of H. pylori in patients with chronic urticaria. We screened an unselected series of patients for infection and investigated whether specific treatment against the pathogen could cure the urticaria.

Permeability of human HT‐29/B6 colonic epithelium as a function of apoptosis

1 The barrier function of colonic epithelia is challenged by apoptotic loss of enterocytes. In monolayers of human colonic HT‐29/B6 cells, apoptosis induced by camptothecin was assessed by poly‐(ADP‐ribose)‐polymerase (PARP) cleavage, histone ELISA and DNA‐specific fluorochrome staining (with 4′,6′‐diamidino‐2′‐phenylindoladihydrochloride (DAPI)). Epithelial barrier function was studied in Ussing chambers by measuring transepithelial conductivity and unidirectional tracer fluxes. The ion permeability associated with single cell apoptoses was investigated with the conductance scanning technique. 2 The spontaneous rate of apoptotic cells was 3.5 ± 0.3 % with an overall epithelial conductivity of 3.2 ± 0.1 mS cm−2. Camptothecin induced a time‐ and dose‐dependent increase of apoptosis and permeability. With 20 μg ml−1 of camptothecin for 48 h, apoptosis increased 4.1‐fold to 14.3 ± 1.5 % and the conductivity doubled to 6.4 ± 1.0 mS cm−2. 3 While 3H‐mannitol flux increased 3.8‐fold and 3H‐lactulose flux increased 2.6‐fold, the flux of 3H‐polyethylene glycol 4000 remained unchanged. Hence, the higher permeability was limited to molecules < 4000 Da. 4 The local epithelial conductivity was higher at the sites of apoptosis than in non‐apoptotic areas. With camptothecin the leaks associated with apoptosis became more numerous and more conductive, while in non‐apoptotic areas the conductivity remained at control level. Hence, the camptothecin‐induced increase in epithelial conductivity reflected the opening of apoptotic leaks and thus the results described, for the first time, epithelial permeability as a function of apoptosis only. 5 The conductivity of apoptotic leaks contributed 5.5 % to the epithelial conductivity of controls and 60 % to the conductivity of monolayers treated with 20 μg ml−1 of camptothecin. Thus apoptosis increased the contribution of paracellular pathways to the overall epithelial permeability. Under control conditions the paracellular conductivity (Gpara) was smaller than the transcellular (Gtrans), but with 12 % apoptosis, Gpara exceeded Gtrans. By definition, the epithelium became ‘leaky’.

Nano- and microscaled particles for drug targeting to inflamed intestinal mucosa—A first in vivo study in human patients

Most of the drugs used in the treatment of inflammatory bowel disease (IBD) become systemically bioavailable and potentially bear strong adverse effects. Targeting the inflamed areas of the intestine and keeping the drug localised at its site of action can reduce adverse effects. In animal studies, luminal uptake into inflamed mucosal areas has been shown to be size dependent. We investigated the potential of nano- and microparticle uptake into the rectal mucosa of human IBD patients. Fluorescently labelled placebo nanoparticles (NP) 250nm in size and microparticles (MP) 3.0μm in size were prepared. 2h after rectal application to patients with Crohns disease (CD) or ulcerative colitis (UC), confocal laser endomicroscopy was performed to visualise the particles in inflamed mucosal areas. In biopsies, ex vivo mucosal transport processes were investigated in miniaturised Ussing chambers. We examined 33 patients with IBD (19 patients with CD, 14 patients with UC) and 6 healthy controls. A significantly enhanced accumulation of MP in ulcerous lesions was observed (covered area=1.28% (range 0.83%-3.45%) vs. 0% in controls; p=0.011), while NP were visible only in traces on mucosal surfaces of all patients. The Ussing chamber experiments suggest persorption of particles through cellular voids; statistical significance was only reached for NP. Drug-containing particles may have great potential to more specifically target intestinal lesions to maximise therapeutic efficacy and minimise potential side effects. Nanoparticles may not be required for local drug delivery to intestinal lesions in humans, thereby minimising the risk of unintended translocation into the blood system.

Risk Factors in the Development of Esophageal Adenocarcinoma

OBJECTIVES:It is assumed that esophageal adenocarcinoma is the end result of a stepwise disease process that transitions through gastroesophageal reflux disease (GERD) and Barretts esophagus. The aim of this study was to examine at what stage known risk factors exert their influence toward the progression to cancer.METHODS:We enrolled 113 consecutive outpatients without GERD, 188 with GERD, 162 with Barretts esophagus, and 100 with esophageal adenocarcinoma or high-grade dysplasia (HGD). All patients underwent a standard upper endoscopy and completed a standardized questionnaire about their social history, symptoms, dietary habits, and prescribed medications. We used adjusted logistic regression analysis to assess risk factors between each two consecutive disease stages from the absence of reflux disease to esophageal adenocarcinoma.RESULTS:Overall, male gender, smoking, increased body mass index (BMI), low fruit and vegetable intake, duration of reflux symptoms, and presence of a hiatal hernia were risk factors for cancer/HGD. However, different combinations of risk factors were associated with different disease stages. Hiatal hernia was the only risk factor to be strongly associated with the development of GERD. For GERD patients, male gender, age, an increased BMI, duration of reflux symptoms, and presence of a hiatal hernia were all associated with the development of Barretts esophagus. Finally, the development of cancer/HGD among patients with Barretts esophagus was associated with male gender, smoking, decreased fruit and vegetable intake, and a long segment of Barretts esophagus, but not with age, BMI, or a hiatal hernia.CONCLUSIONS:While some risk factors act predominantly on the initial development of reflux disease, others appear to be primarily responsible for the development of more advanced disease stages.

Through the endoscope balloon dilation of ileocolonic strictures: prognostic factors, complications, and effectiveness

Background/aimsAbout half of all Crohn’s disease (CD) patients undergo surgery at some point, many because of strictures. An alternative possibility is to dilate strictures endoscopically. However, little is known about prognostic factors.Patients and methodsThirty-two patients with primary CD (n = 2), radiogenic strictures (n = 1), or postoperative strictures (27 because of CD; 2 after resection because of cancer), were planned to undergo colonoscopic dilatation of which 25 patients were dilated (10 men; 15 women; median age 48). Length of stenosis, diameter of stricture, balloon size, smoking status, ulcer in the stricture, passage postdilatation, hemoglobin level, complications, redilatation, and subsequent surgery were recorded. Only patients with at least 6 months follow up were included.ResultsFive out of 32 patients had no stenosis, marked inflammation, or fistulas adjacent to the stricture. One patient each had a long stricture (8cm) or a filiform stenosis ruling out dilatation [technical success, 25/27 (92.6%)]. Among these 25 patients, 39 colonoscopies with 51 dilatations were performed. After a single dilatation, 52% were asymptomatic while 48% needed another intervention, half of them surgery. Bleeding without need for transfusion occurred in 3 out of 39 colonoscopies and one perforation required surgery. Significant prognostic factors were smoking and ulcers in the stricture (P < 0.05 each). Some ulcers led to intussusception requiring surgery in spite of good dilatation results.ConclusionThrough the endoscope balloon stricture dilatation is a relatively safe and often effective treatment modality in ileocolonic strictures. The presence of ulcers in the stricture have a worse outcome as do smokers.