Christian Barmeyer

Altered tight junction structure contributes to the impaired epithelial barrier function in ulcerative colitis

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.

Somatic mutation profiles of MSI and MSS colorectal cancer identified by whole exome next generation sequencing and bioinformatics analysis

Background Colorectal cancer (CRC) is with approximately 1 million cases the third most common cancer worldwide. Extensive research is ongoing to decipher the underlying genetic patterns with the hope to improve early cancer diagnosis and treatment. In this direction, the recent progress in next generation sequencing technologies has revolutionized the field of cancer genomics. However, one caveat of these studies remains the large amount of genetic variations identified and their interpretation. Methodology/Principal Findings Here we present the first work on whole exome NGS of primary colon cancers. We performed 454 whole exome pyrosequencing of tumor as well as adjacent not affected normal colonic tissue from microsatellite stable (MSS) and microsatellite instable (MSI) colon cancer patients and identified more than 50,000 small nucleotide variations for each tissue. According to predictions based on MSS and MSI pathomechanisms we identified eight times more somatic non-synonymous variations in MSI cancers than in MSS and we were able to reproduce the result in four additional CRCs. Our bioinformatics filtering approach narrowed down the rate of most significant mutations to 359 for MSI and 45 for MSS CRCs with predicted altered protein functions. In both CRCs, MSI and MSS, we found somatic mutations in the intracellular kinase domain of bone morphogenetic protein receptor 1A, BMPR1A, a gene where so far germline mutations are associated with juvenile polyposis syndrome, and show that the mutations functionally impair the protein function. Conclusions/Significance We conclude that with deep sequencing of tumor exomes one may be able to predict the microsatellite status of CRC and in addition identify potentially clinically relevant mutations.

Claudin-2 as a mediator of leaky gut barrier during intestinal inflammation

The epithelial tight junction determines the paracellular water and ion movement in the intestine and also prevents uptake of larger molecules, including antigens, in an uncontrolled manner. Claudin-2, one of the 27 mammalian claudins regulating that barrier function, forms a paracellular channel for small cations and water. It is typically expressed in leaky epithelia like proximal nephron and small intestine and provides a major pathway for the paracellular transport of sodium, potassium, and fluid. In intestinal inflammation (Crohns disease, ulcerative colitis), immune-mediated diseases (celiac disease), and infections (HIV enteropathy), claudin-2 is upregulated in small and large intestine and contributes to diarrhea via a leak flux mechanism. In parallel to that upregulation, other epithelial and tight junctional features are altered and the luminal uptake of antigenic macromolecules is enhanced, for which claudin-2 may be partially responsible through induction of tight junction strand discontinuities.

High-Throughput miRNA and mRNA Sequencing of Paired Colorectal Normal, Tumor and Metastasis Tissues and Bioinformatic Modeling of miRNA-1 Therapeutic Applications

MiRNAs are discussed as diagnostic and therapeutic molecules. However, effective miRNA drug treatments with miRNAs are, so far, hampered by the complexity of the miRNA networks. To identify potential miRNA drugs in colorectal cancer, we profiled miRNA and mRNA expression in matching normal, tumor and metastasis tissues of eight patients by Illumina sequencing. We validated six miRNAs in a large tissue screen containing 16 additional tumor entities and identified miRNA-1, miRNA-129, miRNA-497 and miRNA-215 as constantly de-regulated within the majority of cancers. Of these, we investigated miRNA-1 as representative in a systems-biology simulation of cellular cancer models implemented in PyBioS and assessed the effects of depletion as well as overexpression in terms of miRNA-1 as a potential treatment option. In this system, miRNA-1 treatment reverted the disease phenotype with different effectiveness among the patients. Scoring the gene expression changes obtained through mRNA-Seq from the same patients we show that the combination of deep sequencing and systems biological modeling can help to identify patient-specific responses to miRNA treatments. We present this data as guideline for future pre-clinical assessments of new and personalized therapeutic options.

The interleukin-2-deficient mouse model.

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/cm²). 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^–9M aldosterone in vitro as the drop in I_SC (short circuit current) after addition of 10^–4M amiloride. In controls, J_Na was 6.9 ± 0.9 µmol·h^–1·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.

Claudin-related intestinal diseases.

With up to 200 m(2) the human intestine is the organ with the largest absorptive surface of the body. It is lined by a single layer of epithelial cells that separates the host from the environment. The intestinal epithelium provides both, selective absorption of nutrients, ions, and water but also a highly effective barrier function which includes the first line of defense against environmental antigens. The paracellular part of this barrier function is provided by tight junction (TJ) proteins, especially the large family of claudins. Changes in abundance or molecular structure of claudins can generally result in three typical effects, (i) decreased absorptive passage, (ii) increased secretory passage of small solutes and water causing leak flux diarrhea and (iii) increased absorptive passage of macromolecules which may induce inflammatory processes. Several intestinal diseases are associated with such changes that can result in intestinal inflammation and symptoms like weight loss, abdominal pain or diarrhea. This review summarizes our current knowledge on barrier dysfunction and claudin dysregulation in several intestinal diseases gastroenterologists are often faced with, like inflammatory bowel disease, microscopic colitis, celiac disease, irritable bowel syndrome, gallstones and infectious diseases like HIV enteropathy, Campylobacter jejuni and Clostridium perfringens infection.

Ion transport and barrier function are disturbed in microscopic colitis

In this paper, we identify mechanisms of watery diarrhea in microscopic colitis (MC). Biopsies from the sigmoid colon of patients with collagenous colitis and treated lymphocytic colitis were analyzed in miniaturized Ussing chambers for electrogenic sodium transport and barrier function with one‐path impedance spectroscopy. Cytometric bead arrays (CBA) served to analyze cytokine profiles. In active MC, electrogenic sodium transport was diminished and epithelial resistance decreased. CBA revealed a Th1 cytokine profile featuring increased IFN‐γ, TNF‐α, and IL‐1β levels. After four weeks of steroid treatment with budesonide, electrogenic sodium transport recovered while epithelial barrier defects remained. Diarrhea in MC results at least in part from a combination of impaired electrogenic sodium transport and barrier defects. From a therapeutic perspective it can be postulated that the functional importance of loss of ions may be higher than that caused by barrier impairment.

Genomics and epigenomics: new promises of personalized medicine for cancer patients

Recent years have brought about a marked extension of our understanding of the somatic basis of cancer. Parallel to the large-scale investigation of diverse tumor genomes the knowledge arose that cancer pathologies are most often not restricted to single genomic events. In contrast, a large number of different alterations in the genomes and epigenomes come together and promote the malignant transformation. The combination of mutations, structural variations and epigenetic alterations differs between each tumor, making individual diagnosis and treatment strategies necessary. This view is summarized in the new discipline of personalized medicine. To satisfy the ideas of this approach each tumor needs to be fully characterized and individual diagnostic and therapeutic strategies designed. Here, we will discuss the power of high-throughput sequencing technologies for genomic and epigenomic analyses. We will provide insight into the current status and how these technologies can be transferred to routine clinical usage.

Active and passive involvement of claudins in the pathophysiology of intestinal inflammatory diseases

Intestinal inflammatory diseases, four of which are discussed here, are associated with alterations of claudins. In ulcerative colitis, diarrhea and antigen entry into the mucosa occurs. Claudin-2 is upregulated but data on other claudins are still limited or vary (e.g., claudin-1 and -4). Apart from that, tight junction changes contribute to diarrhea via a leak flux mechanism, while protection against antigen entry disappears behind epithelial gross lesions (erosions) and apoptotic foci. Crohn’s disease is additionally characterized by a claudin-5 and claudin-8 reduction which plays an active role in antigen uptake already before gross lesions appear. In microscopic colitis (MC), upregulation of claudin-2 expression is weak and a reduction in claudin-4 may be only passively involved, while sodium malabsorption represents the main diarrheal mechanism. However, claudin-5 is removed from MC tight junctions which may be an active trigger for inflammation through antigen uptake along the so-called leaky gut concept. In celiac disease, primary barrier defects are discussed in the context of candidate genes as PARD3 which regulate cell polarity and tight junctions. The loss of claudin-5 allows small antigens to invade, while the reductions in others like claudin-3 are rather passive events. Taken together, the specific role of single tight junction proteins for the onset and perpetuation of inflammation and the recovery from these diseases is far from being fully understood and is clearly dependent on the stage of the disease, the background of the other tight junction components, the transport activity of the mucosa, and the presence of other barrier features like gross lesions, an orchestral interplay which is discussed in this article.

EndoClot Polysaccharide Hemostatic System in Nonvariceal Gastrointestinal Bleeding: Results of a Prospective Multicenter Observational Pilot Study.

Background and Study Aims: Hemostatic powders have been introduced to improve the management of gastrointestinal (GI) bleeding and to extend the variety of tools available for emergency endoscopy. The aim of the present pilot study was to evaluate the indication profiles and the short-term outcome of EndoClot. Patients, Materials and Methods: In a prospective observational pilot study patients with acute nonvariceal GI bleeding were included. Primary or secondary application of EndoClot was assessed. Hemoglobin, prothrombine time and platelets were documented before and after hemostasis. The efficacy of EndoClot was assessed 72 hours and 1 week after application. Results: Seventy patients with acute GI bleeding were recruited into the study. Eighty-three percent (58/70) of the patients had upper and 17% (12/70) had lower GI bleeding. In the upper GI tract treatment success was achieved in 64% (30/47, 95% confidence interval, 50%-76%) after primary use and in all patients, when used after established techniques had failed (95% confidence interval, 70%-100%). In lower GI bleeding hemostasis was achieved in 83% of cases (10/12, 95% confidence interval 54%-97%). Rebleeding occurred in 11% (8/70), in 10% EndoClot served as a bridge to surgery (7/70). Conclusions: EndoClot expanded the therapeutic options in the management of GI bleeding. It was applicable as a monotherapy or in combination with other techniques from oozing bleeding type or lower. It was most effective in diffuse or extensive bleeding activity or when access to the bleeding vessel was difficult. EndoClot can be applied as a bridge to surgery when classical methods of hemostasis have failed.