The future of GI and liver research: editorial perspectives: I. Visions of epithelial research

Beyond white light endoscopy: The role of optical biopsy in inflammatory bowel disease

In this review, we will discuss the use of two optical biopsy modalities in inflammatory bowel disease (IBD). The two techniques reviewed here are confocal laser endomicroscopy and endocytoscopy. We will describe the technical performance of the procedure, discuss the clinical indications for optical biopsy in IBD, and highlight active research areas with respect to the pathogenesis of IBD. Clinical indications for optical biopsies in IBD include assessment of mucosal inflammation, dysplasia detection and evaluation of cell shedding for disease relapse. Research application in the area of barrier dysfunction will also be discussed.

Breaks in the wall: increased gaps in the intestinal epithelium of irritable bowel syndrome patients identified by confocal laser endomicroscopy (with videos)

BACKGROUND

Altered intestinal permeability and mucosal inflammation have been reported in irritable bowel syndrome (IBS) patients. Increased cell extrusion in the epithelium as measured by epithelial gaps may be associated with barrier dysfunction and may lead to mucosal inflammation. Confocal laser endomicroscopy can be used to identify and quantitate epithelial gaps in the small intestine.

OBJECTIVE

To determine the epithelial gap density in IBS and healthy control patients.

DESIGN

Prospective, controlled cohort study.

SETTING

A tertiary referral center.

PATIENTS

In IBS and control patients undergoing routine colonoscopy, probe-based confocal laser endomicroscopy was used to image the terminal ileum.

MAIN OUTCOME MEASUREMENTS

The primary outcome was the density of epithelial gaps (gaps/cells counted) in adequately imaged villi using pCLE. Images were reviewed by 2 blinded reviewers.

RESULTS

We recruited 18 healthy controls and 16 IBS patients. The median epithelial gap densities for control and IBS patients were 6 and 32 gaps per 1000 cells, respectively (P < .001). There was a trend toward higher gap density in female (P = .07) and younger (ρ = -0.43, P = .07) patients. Using 3% (90% of the control population) as the cutoff for abnormal gap density, we found the diagnostic accuracy for IBS to be as follows: 62% sensitivity, 89% specificity, 83% positive predictive value, and 73% negative predictive value.

LIMITATIONS

A single-center study, small number of patients.

CONCLUSIONS

IBS patients have significantly more epithelial gaps in their small intestine compared with healthy controls, which suggests that increased epithelial cell extrusion may be a cause of altered intestinal permeability observed in IBS.

TNF-α-induced intestinal epithelial cell shedding: implications for intestinal barrier function

Although epithelial cells are continuously shed from the surface of the intestine, the intestinal epithelium maintains the integrity of the epithelial barrier. This is achieved through a highly dynamic process involving reorganization of tight junction and adherens junction proteins. This process both ejects the cell from the epithelial monolayer and plugs the gap left after the cell is shed. Inflammatory insults can trigger a disturbance of these barrier functions by increasing rates of cell shedding. Epithelial cell shedding and loss of barrier can be visualized by confocal laser endomicroscopy in humans. A simple grading system of confocal laser endomicroscopic images can stratify inflammatory bowel disease (IBD) patients in remission into those who will relapse over the subsequent six months and those who will not. Here, we review the mechanisms governing maintenance of these barrier functions and the implications of inflammation-induced barrier dysfunction in IBD.

Increased epithelial gaps in the small intestine are predictive of hospitalization and surgery in patients with inflammatory bowel disease

OBJECTIVES

Epithelial gaps resulting from intestinal cell extrusions can be visualized with confocal laser endomicroscopy (CLE) during colonoscopy and increased in normal-appearing terminal ileum of inflammatory bowel disease (IBD) patients. Cell-shedding events on CLE were found to be predictive of disease relapse. The aim of this study was to assess the prognostic value of epithelial gap densities for major clinical events (hospitalization or surgery) in follow-up.

METHODS

We prospectively followed IBD patients undergoing colonoscopy with probe-based CLE (pCLE) for clinical events including symptom flares, medication changes, hospitalization, or surgery. Survival analysis methods were used to compare event times for the composite outcome of hospitalization or surgery using log-rank tests and Cox proportional hazards models. We also examined the relationship of gap density with IBD flares, need for anti-tumor necrosis factor therapy, disease duration, gender and endoscopic disease severity, and location.

RESULTS

A total of 21 Crohn's disease and 20 ulcerative colitis patients with a median follow-up of 14 (11-31) months were studied. Patients with elevated gap density were at significantly higher risk for hospitalization or surgery (log-rank test P=0.02). Gap density was a significant predictor for risk of major events, with a hazard ratio of 1.10 (95% confidence interval=1.01, 1.20) associated with each increase of 1% in gap density. Gap density was also correlated with IBD disease duration (Spearman's correlation coefficient rho=0.44, P=0.004), and was higher in male patients (9.0 vs. 3.6 gaps per 100 cells, P=0.038).

CONCLUSIONS

Increased epithelial gaps in the small intestine as determined by pCLE are a predictor for future hospitalization or surgery in IBD patients.

Identification of epithelial gaps in human small and large intestine by confocal endomicroscopy

BACKGROUND & AIMS

Confocal endomicroscopy is an emerging technology that poses the endoscopist with challenges for identifying epithelial structures in the human intestine. We have shown previously that the murine intestinal epithelium is punctuated by gaps caused by cell shedding. The goals of this study were to determine if confocal endomicroscopy could resolve the presence of human epithelial gaps and whether a proinflammatory cytokine could increase cell shedding.

METHODS

Intestinal mucosa was imaged after staining with acriflavine. Confocal endomicroscopy of 17 patients yielded 6277 images from the human terminal ileum and rectum. Results were validated by parallel studies of anesthetized mice (wild-type and Math1(DeltaIntestine)) using rigid confocal probe microscopy, 2-photon/confocal microscopy, and scanning electron microscopy.

RESULTS

Human terminal ileal and rectal epithelium revealed unstained areas with the diameter of an individual epithelial cell, with 2 distinct morphologies. One had a "target" appearance, shown by mouse studies to be goblet cells. The other morphology had no nucleus and was observed by rigid confocal probe microscopy and scanning electron microscopy in the villi of Math1(DeltaIntestine) mice, which lack goblet cells. In the mouse, tumor necrosis factor alpha (0.33 microg/g intraperitoneally) increases cell shedding by 27-fold and caused loss of barrier function across 20% of resultant gaps.

CONCLUSIONS

Confocal endomicroscopy can distinguish between epithelial discontinuities (gaps) and goblet cells in human intestine. Results suggest that the sealing of epithelial gaps must be considered as a component of the intestinal barrier and has potential implications for intestinal barrier dysfunction in human disease.

Characterization of epithelial cell shedding from human small intestine

Intestinal epithelial cells migrate from the base of the crypt to the villi where they are shed. However, little is known about the cell shedding process. We have studied the role of apoptosis and wound healing mechanisms in cell shedding from human small intestinal epithelium. A method preparing paraffin sections of human small intestine that preserves cell shedding was developed. A total of 14 417 villus sections were studied. The relationship of cell shedding to leukocytes (CD45), macrophages (CD68) and blood vessels (CD34) were studied by immunohistochemistry. Apoptotic cells were identified using the M30 antibody against cleaved cytokeratin 18 and an antibody against cleaved caspase-3. Potential wound healing mechanisms were studied using antibodies against Zona Occludens-1 (ZO-1) and phosphorylated myosin light chains (MLCs). We found that 5.3% of villus sections contained a shedding cell. An eosin-positive gap was often seen within the epithelial monolayer beneath shedding cells. Shedding was not associated with leukocytes, macrophages or blood vessels. Cells always underwent apoptosis during ejection from the monolayer. Apoptotic bodies were never seen in the monolayer but morphologically normal cells that were positive for M30 or cleaved caspase-3 were often seen. ZO-1 protein was usually (41/42) localized to the apical pole of cells neighboring a shedding event. Phosphorylated MLCs could be identified in 50% of shedding events. In conclusion, cell shedding is associated with apoptosis though it remains unclear whether apoptosis initiates shedding. It is also associated with phosphorylation of MLCs; a process associated previously with wound healing.

Epithelial barrier function in vivo is sustained despite gaps in epithelial layers

BACKGROUND & AIMS

Epithelial cells of the small intestine migrate to the tip of the villus at which they are shed. It is not understood how the intestinal barrier is maintained during this high cell turnover. The aim of this study was to use high-resolution in vivo light microscopy to investigate the mechanism of epithelial shedding and the site of the permeability barrier during cell shedding.

METHODS

A laparotomy was performed on anesthetized mice, and a segment of small intestine was opened. The exposed epithelial surface of the intestine was imaged by multiphoton microscopy. Nuclei, cytosol, and cell membranes were imaged using the dyes Hoescht 33258, BCECF, a transgenically expressed fluorescent protein, and the membrane dye DiI. The fluorescent caspase substrate PhiPhiLux was used to detect apoptosis.

RESULTS

In the epithelial monolayer, gaps were observed that lacked nuclei or cytosol but appeared to be filled with an impermeable substance. Studies with membrane impermeant fluorophores (Lucifer Yellow and Alexa-dextran) showed that the impermeable substance completely fills the void left by the absent cell. Only a fraction of gaps have either ZO-1 staining or cytoplasmic extensions from neighboring cells at the basal pole. Time-lapse studies reveal that cell shedding results in genesis of a gap and that shedding usually occurs prior to detectable cellular activation of caspase 3 or nuclear condensation.

CONCLUSIONS

Results suggest that epithelial barrier function is sustained at the apical pole of the epithelial layer, despite discontinuities in the cellular layer.

Development of a porcine small intestinal cDNA micro-array: characterization and functional analysis of the response to enterotoxigenic E. coli

The intestine is a complex and dynamic ecosystem, in which nutrients, exogenous compounds and micro-flora interact, and its condition is influenced by the complex interaction between these factors and host genetic elements. Furthermore, interactions of immune cells with the other components of the intestinal mucosa are essential in the defense against pathogens. The outcomes of these complex interactions determine resistance to infectious diseases. The development of genomic tools and techniques allows for analysis of multiple and complex host responses. We have constructed a porcine small intestinal micro-array, based on cDNA from jejunal mucosal scrapings. Material from two developmental distinct stages (4- and 12-week-old pigs) was used in order to assure a reasonably broad representation of mucosal transcripts. The micro-array consists of 3468 cDNAs spotted in quadruplicate. Comparison of the 4-week-old versus 12-week-old pigs revealed a differential expression in at least 300 spots. Furthermore, we report the early gene expression response of pig small intestine jejunal mucosa to infection with enterotoxigenic E. coli (ETEC) using the small intestinal segment perfusion (SISP) technique. A response pattern was found in which a marker for innate defense dominated, demonstrating the strength of this applied technology. Further analysis of these response patterns will contribute to a better understanding of enteric health and disease in pigs. The great similarity between pig and human suggest results from these continuing studies should be applicable for both agricultural and human biomedical purposes.