Neutrophil transmigration in inflammatory bowel disease is associated with differential expression of epithelial intercellular junction proteins

Synthesis and structure-activity relationships of 3,4-diaminocyclobut-3-ene-1,2-dione CXCR2 antagonists

A novel series of 3,4-diaminocyclobut-3-ene-1,2-diones was prepared and found to show potent inhibitory activity of CXCR2 binding and IL-8-mediated chemotaxis of a CXCR2-expressing cell line. Microsome stability and Caco2 studies were subsequently used to show that compounds of this chemotype are predicted to have good oral bioavailability and are thus suitable for pharmaceutical development.

Safety and efficacy of extracorporeal granulocyte and monocyte adsorption apheresis in patients with severe persistent bronchial asthma

The Adacolumn is an adsorptive-type extracorporeal device, which is filled with cellulose diacetate beads that selectively adsorb granulocytes and monocytes. Patients with severe persistent asthma experience highly variable continuous symptoms and severe exacerbations in spite of medication based on inhaled glucocorticosteroids. Granulocyte and monocyte adsorption apheresis using extracorporeal circulation through the Adacolumn was performed in nine patients with severe persistent asthma. The extracorporeal circulation through the Adacolumn was performed once a week for 5 weeks. We were able to perform this therapy without any severe adverse effects in all patients, although one patient complained of general fatigue just after the circulations. In six of the nine patients, the increase in peak expiratory flow (PEF) was more than 50 mL/min. The average increase in morning PEF was 23.3% while that in the evening PEF was 26.4% after the therapy. This therapy was not harmful for patients with severe persistent asthma. A placebo-controlled study will be desired to evaluate the efficacy of this nonpharmacological strategy accurately.

Serum antibodies to EpCAM in healthy donors but not ulcerative colitis patients

PURPOSE

The gastrointestinal carcinoma-associated antigen epithelial cell adhesion molecule (EpCAM) has been a target for passive and active immunotherapy of gastrointestinal carcinoma patients. The antigen is expressed by both tumor and normal tissues. The immunogenicity of EpCAM in colorectal cancer patients has been described previously. The purpose of this study was to evaluate humoral and cellular immune responses of healthy individuals and ulcerative colitis patients to EpCAM and to relate immune responses to colonic tissue expression of EpCAM.

METHODS

An inhibition radioimmunoassay was used to detect anti-EpCAM serum antibodies. Anti-EpCAM antibodies of a healthy donor were expressed by phages and sequenced. (3)H-thymidine incorporation assay was used for detection of lymphoproliferative responses to stimulation with EpCAM. EpCAM tissue expression was determined by immunohistochemistry.

RESULTS

We detected anti-EpCAM serum antibodies in 4 of 10, and EpCAM-specific lymphoproliferation responses in 1 of 10 healthy volunteers. The majority of anti-EpCAM antibodies derived from a healthy donor were germline-encoded. In contrast, none of the 23 patients with ulcerative colitis showed serum antibodies to EpCAM (P=0.005). Antigen expression was greatly reduced and altered in ulcerative colitis patients, whereas colon from healthy individuals and uninvolved colon of colorectal cancer patients expressed high levels of EpCAM.

CONCLUSION

The results of these studies suggest an association between EpCAM antibody production and colonic EpCAM expression in healthy individuals and patients with ulcerative colitis. Decreased and altered colonic EpCAM expression in ulcerative colitis patients may be related to the disease induction, based on the previously demonstrated adhesion function of this molecule. Healthy individuals with anti-EpCAM immune responses and high risk for developing colorectal carcinoma are prime candidates for prophylactic immunization against EpCAM.

Unique dietary-related mouse model of colitis

BACKGROUND

A high-fat diet is a risk factor for the development of inflammatory bowel disease (IBD) in humans. Deoxycholate (DOC) is increased in the colonic contents in response to a high-fat diet. Thus, an elevated level of DOC in the colonic lumen may play a role in the natural course of development of IBD.

METHODS

Wild-type B6.129 mice were fed an AIN-93G diet, either supplemented with 0.2% DOC or unsupplemented and sacrificed at 1 week, 1 month, 3 months, 4 months, and 8 months. Colon samples were assessed by histopathological, immunohistochemical, and cDNA microarray analyses.

RESULTS

Mice fed the DOC-supplemented diet developed focal areas of colonic inflammation associated with increases in angiogenesis, nitrosative stress, DNA/RNA damage, and proliferation. Genes that play a central role in inflammation and angiogenesis and other related processes such as epithelial barrier function, oxidative stress, apoptosis, cell proliferation/cell cycle/DNA repair, membrane transport, and the ubiquitin-proteasome pathway showed altered expression in the DOC-fed mice compared with the control mice. Changes in expression of individual genes (increases or reductions) correlated over time. These changes were greatest 1 month after the start of DOC feeding.

CONCLUSIONS

The results suggest that exposure of the colonic mucosa to DOC may be a key etiologic factor in IBD. The DOC-fed mouse model may reflect the natural course of development of colitis/IBD in humans, and thus may be useful for determining new preventive strategies and lifestyle changes in affected individuals.

Regulation of the intestinal epithelial barrier by the apical junctional complex

PURPOSE OF REVIEW

Epithelial intercellular junctions are important components of the epithelial barrier and are compromised in disorders such as Crohn's disease. We will highlight recent progress in understanding the role of an intercellular junction referred to as the apical junctional complex in regulating small intestinal epithelial permeability in health and disease.

RECENT FINDINGS

Recent studies have implicated aberrant regulation of the AJC as an underlying factor contributing to a leaky epithelial barrier in Crohn's patients. Consequences of increased epithelial permeability include exposure of intestinal tissue to luminal antigens/pathogens which in turn influence disease activity. Furthermore, proinflammatory cytokines released into the milieu of the epithelium in patients with Crohn's disease influence apical junctional complex and epithelial barrier function. Such cytokines induce disassembly of the apical junctional complex by promoting differential endocytosis of component proteins. Additionally, apical junctional complex proteins are targeted by pathogens that use the epithelium as a portal of entry to establish disease in the host.

SUMMARY

The epithelial apical junctional complex is important in determining epithelial barrier properties. Recent studies have highlighted contribution of proinflammatory cytokines and endocytosis of apical junctional complex proteins to the epithelial barrier defect. Continued advances in understanding of this field will yield new therapeutic targets for intestinal disorders.

The primary defect in experimental ileitis originates from a nonhematopoietic source

The initiating etiologic factor in Crohn's disease (CD) remains unclear. SAMP1/YitFc (SAMP) mice develop chronic ileitis similar to human CD. We used bone marrow chimeras to determine if SAMP ileitis results from a primary immunological defect or from dysregulated mucosal immunity secondary to intrinsic, nonhematopoietic (e.g., epithelial) dysfunction. SAMP mice receiving wild-type (AKR) BM developed severe ileitis, whereas SAMP BM did not confer ileitis to WT recipients. WT lymphocytes from reconstituted SAMP mice resembled native SAMP populations in regard to surface phenotype and cytokine production. Ilea from native SAMP mice and SAMP recipients of wild-type BM displayed decreased epithelial barrier resistance ex vivo and increased epithelial permeability in vivo compared to native WT mice and AKR recipients of SAMP BM. This permeability defect preceded the development of ileal inflammation, was present in the absence of commensal bacteria, and was accompanied by altered ileal mRNA expression of the tight junction proteins claudin-2 and occludin. Our results provide evidence that the primary defect conferring ileitis in SAMP mice originates from a nonhematopoietic source. Generation of pathogenic lymphocytes is a consequence of this defect and does not reflect intrinsic proinflammatory leukocyte properties. Decreased barrier function suggests that defects in the epithelium may represent the primary source of SAMP ileitis susceptibility.

Roles of ZO-1, occludin, and actin in oxidant-induced barrier disruption

Oxidants such as monochloramine (NH(2)Cl) decrease epithelial barrier function by disrupting perijunctional actin and possibly affecting the distribution of tight junctional proteins. These effects can, in theory, disturb cell polarization and affect critical membrane proteins by compromising molecular fence function of the tight junctions. To examine these possibilities, we investigated the actions of NH(2)Cl on the distribution, function, and integrity of barrier-associated membrane, cytoskeletal, and adaptor proteins in human colonic Caco-2 epithelial monolayers. NH(2)Cl causes a time-dependent decrease in both detergent-insoluble and -soluble zonula occludens (ZO)-1 abundance, more rapidly in the former. Decreases in occludin levels in the detergent-insoluble fraction were observed soon after the fall of ZO-1 levels. The actin depolymerizer cytochalasin D resulted in a decreased transepithelial resistance (TER) more quickly than NH(2)Cl but caused a more modest and slower reduction in ZO-1 levels and in occludin redistribution. No changes in the cellular distribution of claudin-1, claudin-5, or ZO-2 were observed after NH(2)Cl. However, in subsequent studies, the immunofluorescent cellular staining pattern of all these proteins was altered by NH(2)Cl. The actin-stabilizing agent phalloidin did not prevent NH(2)Cl-induced decreases in TER or increases of apical to basolateral flux of the paracellular permeability marker mannitol. However, it partially blocked changes in ZO-1 and occludin distribution. Tight junctional fence function was also compromised by NH(2)Cl, observed as a redistribution of the alpha-subunit of basolateral Na(+)-K(+)-ATPase to the apical membrane, an effect not found with the apical membrane protein Na(+)/H(+) exchanger isoform 3. In conclusion, oxidants not only disrupt perijunctional actin but also cause redistribution of tight junctional proteins, resulting in compromised intestinal epithelial barrier and fence function. These effects are likely to contribute to the development of malabsorption and dysfunction associated with mucosal inflammation of the digestive tract.

Abrogation of IFN-gamma mediated epithelial barrier disruption by serine protease inhibition

The intestinal barrier function is often impaired in a variety of diseases including chronic inflammatory bowel disease. Increased intestinal permeability during episodes of active disease correlates with destruction or rearrangement of the tight junction protein complex. IFN-gamma has been widely studied for its effect on barrier function and tight junction structures but its mode of action remains unclear. Since the claudin family of tight junction proteins is proposed to be involved in barrier maintenance we studied the effect of IFN-gamma on claudin expression in relation to epithelial barrier function. Cycloheximide and protease inhibitors were used to study mechanisms of IFN-gamma mediated barrier disruption. Intestinal epithelial cells were exposed to IFN-gamma and permeability was evaluated by horse radish peroxidase (HRP) and 4 kD FITC-dextran fluxes. Occludin and claudin-1, -2, -3, and -4 tight junction protein expression was determined by Western blotting. Occludin and claudin-2 protein expression was dramatically reduced after IFN-gamma exposure, which correlated with increased permeability for HRP and FITC-dextran. Interestingly, cleavage of claudin-2 was observed after incubation with IFN-gamma. Serine protease inhibitor AEBSF completely abrogated IFN-gamma mediated barrier disruption which was associated with preservation of claudin-2 expression. Moreover, IFN-gamma induced loss of barrier integrity was found to affect claudin-2 and occludin expression through different mechanisms. Since inhibition of serine protease activity abrogates IFN-gamma mediated barrier disruption this may be an important target for therapeutic intervention.

Eosinophils alter colonic epithelial barrier function: role for major basic protein

Mucosal eosinophils increase in a number of gastrointestinal diseases that are often associated with altered epithelial barrier function, including food allergic enteropathies and inflammatory bowel diseases. Although eosinophils are known to secrete biologically active mediators including granule proteins, their role in gastrointestinal diseases is uncertain. The aim of this study was to determine the impact of eosinophils on intestinal barrier function. Epithelial barrier function was determined in a coculture of eosinophils and T84 epithelial cells and in a murine model of T helper (Th) type 2-mediated colitis. Coculture conditions resulted in decreased transepithelial resistance (TER) and increased transepithelial flux. Cell-free coculture supernatants contained a > or =5-kDa soluble factor that also diminished TER; these supernatants contained the eosinophil-granule proteins major basic protein (MBP) and eosinophil-derived neurotoxin (EDN). T84 barrier function decreased significantly when basolateral surfaces were exposed to native human MBP but not EDN. Additional studies identified downregulation of the tight junctional molecule occludin as at least one mechanism for MBP action. MBP-null mice were protected from inflammation associated with oxazolone colitis compared with wild-type mice. In conclusion, MBP decreases epithelial barrier function and in this manner contributes to the pathogenesis of inflammatory bowel diseases.

Interferon-gamma selectively increases epithelial permeability to large molecules by activating different populations of paracellular pores

Impairment of the gut epithelial barrier by agents such as IFNgamma may play a key role in the pathogenesis of inflammatory disorders by increasing the paracellular penetration of luminal macromolecules, potentially including bacterial antigens. Owing to limitations of current paracellular probes, little is known about the precise functional changes induced by IFNgamma and how these relate to the development of increased macromolecular permeability. Here we investigate how IFNgamma modulates this pathway in T84 monolayers using a novel profiling technique that resolves different populations of paracellular pores by simultaneous analysis of 24 permeability probes of defined molecular size. Two types of functional pore present in control monolayers, an abundant restrictive pore with a radius of approximately 4.5 Angstrom and a much larger but infrequent, non-restrictive pore, were differentially regulated by IFNgamma. Incubation with IFNgamma dose-dependently and reversibly increased the frequency of the non-restrictive pores while having no significant effect on the restrictive component. Cytokine-induced increases in beta, the descriptor of the non-restrictive pore, correlated closely with increased permeability to large molecules (10 kDa) including E. coli-derived lipopolysaccharide, but not small (0.182 kDa) molecules. This effect was associated with changes in expression of the tight junction proteins occludin and claudin-1. These data suggest that IFNgamma selectively increases the transepithelial flux of large molecules by activating specific pathways within the junctional pore. One hypothesis is that this process may be activated in the early stages of the inflammatory response, facilitating the passage of large and potentially antigenic molecules across the gut without gross disruption of the barrier to small molecules.

Enteropathogenic E. coli disrupts tight junction barrier function and structure in vivo

Enteropathogenic Escherichia coli (EPEC) infection disrupts tight junctions (TJs) and perturbs intestinal barrier function in vitro. E. coli secreted protein F (EspF) is, in large part, responsible for these physiological and morphological alterations. We recently reported that the C57BL/6J mouse is a valid in vivo model of EPEC infection as EPEC colonizes the intestinal epithelium and effaces microvilli. Our current aim was to examine the effects of EPEC on TJ structure and barrier function of the mouse intestine and to determine the role of EspF in vivo. C57BL/6J mice were gavaged with approximately 2 x 10(8) EPEC organisms or PBS. At 1 or 5 days postinfection, mice were killed and ileal and colonic tissue was mounted in Ussing chambers to determine barrier function (measured as transepithelial resistance) and short circuit current. TJ structure was analyzed by immunofluorescence microscopy. Wild-type (WT) EPEC significantly diminished the barrier function of ileal and colonic mucosa at 1 and 5 days postinfection. Deficits in barrier function correlated with redistribution of occludin in both tissues. Infection with an EPEC strain deficient of EspF (delta espF) had no effect on barrier function at 1 day postinfection. Furthermore, delta espF had no effect on ileal TJ morphology and minor alterations of colonic TJ morphology at 1 day postinfection. In contrast, at 5 days postinfection, WT EPEC and delta espF had similar effects on barrier function and occludin localization. In both cases this was associated with immune activation, as demonstrated by increased mucosal tumor necrosis factor-alpha levels 5 days postinfection. In conclusion, these data demonstrate that WT EPEC infection of 6-8-week-old C57BL/6J mice (1) significantly decreases barrier function in the ileum and colon (2) redistributes occludin in the ileum and colon and (3) is dependent upon EspF to induce TJ barrier defects at early, but not late, times postinfection.

Inflammatory processes have differential effects on claudins 2, 3 and 4 in colonic epithelial cells

Claudin proteins comprise a recently described family of tight junction proteins that differentially regulate paracellular permeability. Since other tight junction proteins show alterations in distribution or expression in inflammatory bowel disease (IBD) we assessed expression of claudins (CL) 2, 3 and 4 in IBD. CL 2 was strongly expressed along the inflamed crypt epithelium, whilst absent or barely detectable in normal colon. In contrast, CL 3 and 4 were present throughout normal colonic epithelium and were reduced or redistributed in the diseased surface epithelium. In a T84-cell culture model of the gut barrier, paracellular permeability decreased with time after plating and correlated with a marked decrease in the expression of CL 2. Addition of IFNgamma/TNFalpha led to further decreases in CL 2 and 3, the redistrbution of CL 4 and a marked increase in paracellular permeability. Conversely, IL-13 dramatically increased CL 2, with little effect on CL 3 or 4, but also resulted in increased paracellular permeability. Expression of CL 2 did not correlate with proliferation or junctional reorganisation after calcium ion depletion. Re-expression of CL 2 in response to IL-13 was inhibited by phophatidylinositol 3 kinase inhibitor, LY294002, which also restored the ion permeability to previous levels. CL 2 expression could be stimulated in the absence of IL-13 by activation of phospho-Akt in the phophatidylinositol 3 kinase pathway. These results suggest that INFgamma/TNFalpha and IL-13 have differential effects on CL 2, 3 and 4 in tight junctions, which may lead to increased permeability via different mechanisms.

Mucosal integrity and barrier function in the pathogenesis of early lesions in Crohn's disease

Crohn's disease aetiology is multifactorial and remains enigmatic. However, animal models show that disease heterogeneity is probable, in that more than one defective mucosal mechanism can produce the same clinical phenotype. For example, Crohn's-like lesions are reported after compromise of mucosal integrity per se in the presence of an intact immune system, through altered expression of mucosal adhesion molecules, such as cadherins and tight junction proteins, highlighting the importance of the mucosal barrier in the disease process. Key to mucosal damage is the trigger of an inflammatory cascade after luminal antigen processing, a role classically ascribed to M cells in the surface follicle associated epithelium. Direct luminal antigen sampling has recently been proposed, however, by extension of dendritic cell (DC) processes through the intact gut epithelium, and it follows that early mucosal damage could result from de novo lymphoid recruitment. Cytokines, such as tumour necrosis factor alpha (TNFalpha), are known to drive inflammation, but emerging data suggest additional important roles for TNFalpha influencing mucosal barrier efficacy by altering adhesion molecule expression, influencing epithelial apoptosis, and affecting tight junction functionality.

Amphiregulin causes functional downregulation of adherens junctions in psoriasis

Overexpression of amphiregulin (AR) has been linked to psoriasis in mouse and man. Since psoriasis is marked by hyperproliferation of keratinocytes and loss of epidermal barrier function with infiltration of inflammatory cells into the epidermis and dermis, we hypothesized that AR might contribute to the pathogenesis of psoriasis by affecting the integrity of cell-cell junctions. We find that there is a marked reduction of functional E-cadherin in psoriatic lesions from both INV-AR mice and individuals with psoriasis. Total E-cadherin levels are dramatically reduced in psoriatic lesions from INV-AR mice. Compared with normal skin, psoriatic lesions from individuals with psoriasis exhibit downregulation of the cytoskeletal-associated triton-insoluble pool of E-cadherin and the appearance of an 80 kDa ectodomain fragment in the cytoplasmic triton-soluble pool. There is reduced immunohistochemical staining for E-cadherin in the basal epidermis of human psoriatic lesions. Moreover, there is enhanced transmigration of human neutrophils through polarized epithelial cell monolayers of MDCK cells after administration of AR, but not transforming growth factor-alpha, further supporting a specific role for AR in the pathogenesis of psoriasis.

Altered localization and expression of tight-junction proteins in a rat model with chronic acid reflux esophagitis

BACKGROUND

The esophageal tight junction is responsible for the paracellular sealing of the epithelium. Alteration of the expression of tight-junction proteins plays crucial roles in the pathogenesis of some human diseases. The aim of this study was to investigate the distribution and expression pattern of tight-junction proteins in the esophageal mucosa of control rats and rats with reflux esophagitis.

METHODS

Chronic acid reflux esophagitis was experimentally induced by operation in rats. The animals were killed on days 7 and 14 after the operation. The thickness of the mucosa and the 5-bromo-2-deoxyuridine (BrdU) labeling index were assessed. The expression pattern of the tight-junction proteins claudin 1-4 and occludin in the esophageal mucosa was investigated by immunofluorescence staining and Western blotting in the controls and esophagitis rats.

RESULTS

In the esophagitis model, the thickness and BrdU labeling index increased with time. In control rats, claudin-1, -3, and -4 were localized on the cellular membranes of esophageal epithelial cells, mainly in the spinous and granular layers, while claudin-2 was not detected in any layer. Occludin was seen on the cellular membranes in all esophageal mucosal layers. In the esophagitis rats, the expression of claudin-1 was increased both in the plasma membrane and in the cytoplasm around the erosion in the spinous and granular layers. The expression of claudin-4 and occludin shifted to the cytoplasm from the plasma membrane in the spinous and granular layers. In contrast, the expression of claudin-3 was decreased in the spinous and granular layers.

CONCLUSIONS

The localization and the expression patterns of tight-junction proteins were different in the controls and the rat esophagitis model. The expression of claudin-3 in the esophageal mucosa was decreased, while that of claudin-1 was increased. It is postulated that these alterations in tight-junction proteins most likely increase the permeability of the esophageal the epithelium, thereby impairing the defense mechanism of this epithelium.

Dissection of the inflammatory bowel disease transcriptome using genome-wide cDNA microarrays

BACKGROUND

The differential pathophysiologic mechanisms that trigger and maintain the two forms of inflammatory bowel disease (IBD), Crohn disease (CD), and ulcerative colitis (UC) are only partially understood. cDNA microarrays can be used to decipher gene regulation events at a genome-wide level and to identify novel unknown genes that might be involved in perpetuating inflammatory disease progression.

METHODS AND FINDINGS

High-density cDNA microarrays representing 33,792 UniGene clusters were prepared. Biopsies were taken from the sigmoid colon of normal controls (n = 11), CD patients (n = 10) and UC patients (n = 10). 33P-radiolabeled cDNA from purified poly(A)+ RNA extracted from biopsies (unpooled) was hybridized to the arrays. We identified 500 and 272 transcripts differentially regulated in CD and UC, respectively. Interesting hits were independently verified by real-time PCR in a second sample of 100 individuals, and immunohistochemistry was used for exemplary localization. The main findings point to novel molecules important in abnormal immune regulation and the highly disturbed cell biology of colonic epithelial cells in IBD pathogenesis, e.g., CYLD (cylindromatosis, turban tumor syndrome) and CDH11 (cadherin 11, type 2). By the nature of the array setup, many of the genes identified were to our knowledge previously uncharacterized, and prediction of the putative function of a subsection of these genes indicate that some could be involved in early events in disease pathophysiology.

CONCLUSION

A comprehensive set of candidate genes not previously associated with IBD was revealed, which underlines the polygenic and complex nature of the disease. It points out substantial differences in pathophysiology between CD and UC. The multiple unknown genes identified may stimulate new research in the fields of barrier mechanisms and cell signalling in the context of IBD, and ultimately new therapeutic approaches.

Mechanism of IFN-gamma-induced endocytosis of tight junction proteins: myosin II-dependent vacuolarization of the apical plasma membrane

Disruption of epithelial barrier by proinflammatory cytokines such as IFN-gamma represents a major pathophysiological consequence of intestinal inflammation. We have previously shown that IFN-gamma increases paracellular permeability in model T84 epithelial cells by inducing endocytosis of tight junction (TJ) proteins occludin, JAM-A, and claudin-1. The present study was designed to dissect mechanisms of IFN-gamma-induced endocytosis of epithelial TJ proteins. IFN-gamma treatment of T84 cells resulted in internalization of TJ proteins into large actin-coated vacuoles that originated from the apical plasma membrane and resembled the vacuolar apical compartment (VAC) previously observed in epithelial cells that lose cell polarity. The IFN-gamma dependent formation of VACs required ATPase activity of a myosin II motor but was not dependent on rapid turnover of F-actin. In addition, activated myosin II was observed to colocalize with VACs after IFN-gamma exposure. Pharmacological analyses revealed that formation of VACs and endocytosis of TJ proteins was mediated by Rho-associated kinase (ROCK) but not myosin light chain kinase (MLCK). Furthermore, IFN-gamma treatment resulted in activation of Rho GTPase and induced expressional up-regulation of ROCK. These results, for the first time, suggest that IFN-gamma induces endocytosis of epithelial TJ proteins via RhoA/ROCK-mediated, myosin II-dependent formation of VACs.

Changes of occludin expression in intestinal mucosa after burn in rats

In severely burned rats, hyperemia, edema and other pathological injuries occur in the intestinal mucosa. Ultramicroscopically, the microvilli, tight junction and organelles are disrupted. Occludin is a functional component of tight junctions. The purpose of the present study is to investigate changes of occludin expression, and to further elucidate the relationship between occludin expression and ultrastructure damage. The fluorescence intensity of occludin was detected in intestinal wall by the method of immunofluorescence histochemistry and confocal laser scanning microscopy (CLSM). Expression of occludin and its mRNA were determined by western blotting and RT-PCR, respectively. Changes of intestinal mucosa ultrastructure were observed by TEM. The results showed that fluorescence intensity of occludin at 3PBH was enhanced, higher than that of the control group, being 80.77+/-8.38 and 72.86+/-4.74, respectively, and reached a peak at 12PBH (116.14+/-6.89). The expression levels of occludin at 3PBH and 6PBH were 1.21+/-0.02 and 1.53+/-0.14 times that of the control group, respectively, and there were significant differences (P<0.01) between 3PBH group and 6PBH group and control group. The levels of occludin mRNA were also enhanced. At 12PBH, the level reached a peak (P<0.01), being 2.00+/-0.24 times that of the control group. Coincidently, the structure of the tight junction between epithelial cells was disrupted on a large scale under TEM. We speculate that up-regulation of epithelial occludin may play a role in enhancing paracellular permeability and be related to the damage to the tight junction.

Polyamines are necessary for synthesis and stability of occludin protein in intestinal epithelial cells

Occludin is an integral membrane protein that forms the sealing element of tight junctions and is critical for epithelial barrier function. Polyamines are implicated in multiple signaling pathways driving different biological functions of intestinal epithelial cells (IEC). The present study determined whether polyamines are involved in expression of occludin and play a role in intestinal epithelial barrier function. Studies were conducted in stable Cdx2-transfected IEC-6 cells (IEC-Cdx2L1) associated with a highly differentiated phenotype. Polyamine depletion by alpha-difluoromethylornithine (DFMO) decreased levels of occludin protein but failed to affect expression of its mRNA. Other tight junction proteins, zonula occludens (ZO)-1, ZO-2, claudin-2, and claudin-3, were also decreased in polyamine-deficient cells. Decreased levels of tight junction proteins in DFMO-treated cells were associated with dysfunction of the epithelial barrier, which was overcome by exogenous polyamine spermidine. Decreased levels of occludin in polyamine-deficient cells was not due to the reduction of intracellular-free Ca(2+) concentration ([Ca(2+)](cyt)), because either increased or decreased [Ca(2+)](cyt) did not alter levels of occludin in the presence or absence of polyamines. The level of newly synthesized occludin protein was decreased by approximately 70% following polyamine depletion, whereas its protein half-life was reduced from approximately 120 min in control cells to approximately 75 min in polyamine-deficient cells. These findings indicate that polyamines are necessary for the synthesis and stability of occludin protein and that polyamine depletion disrupts the epithelial barrier function, at least partially, by decreasing occludin.

Changes in intestinal morphology and permeability in the biobreeding rat before the onset of type 1 diabetes

OBJECTIVE

Type 1 diabetes is an autoimmune disorder that occurs in genetically susceptible individuals. It has been hypothesized that the disease could be triggered by environmental agents that gain entry into the body through small intestinal absorption. Increased intestinal permeability has been reported both in spontaneous animal models of type 1 diabetes and human type 1 diabetes. In these studies, we examined both the physical and functional permeability characteristics of the small intestine in diabetes-prone and control rats.

METHODS

In a series of studies, BioBreeding diabetes-prone(n = 31), BioBreeding diabetes-resistant (n = 20) and control Wistar (n = 25) rats were examined at intervals from 21 to 125 days of age.

RESULTS

The percentage of goblet cells and the mucosal crypt depth were significantly greater in BioBreeding diabetes-prone than BioBreeding diabetes-resistant rats (P < 0.001 and P = 0.01, respectively). BioBreeding diabetes-prone and BioBreeding diabetes-resistant rats expressed less of the tight junction protein claudin (P < 0.05) and exhibited greater intestinal permeability (P < 0.001) than did Wistar rats. Intestinal permeability measured both in vivo and ex vivo decreased in all rat strains as age increased (P < 0.001).

CONCLUSIONS

In a genetically susceptible rodent model of diabetes, early increased intestinal permeability might allow unregulated passage of environmental antigens that could potentially trigger the autoimmune response leading to type 1 diabetes.

Exacerbation of intestinal permeability in rats after a two-hit injury: burn and Enterococcus faecalis infection

OBJECTIVE

To determine alterations in intestinal epithelial permeability to solutes in burn injured rats with and without Enterococcus faecalis infection and the role of neutrophils in the intestinal permeability changes.

DESIGN

Prospective sham-controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats were subjected to 30% total body surface burn (B group), E. faecalis infection (EF group) induced via intra-abdominal implantation of bacterial pellet, or combination of burn injury and E. faecalis infection (B+EF group).

MEASUREMENTS AND MAIN RESULTS

In vivo measurements of intestinal permeability were carried out after intraluminal injection of H lactulose and C mannitol in the ileum of sham, B, EF, and B+EF groups of rats, 1 and 2 days after injury. Lactulose permeability was increased in the injured rat groups (B, EF, B+EF) on day 1 postinjury compared with sham. The combined injury group (B+EF) had the highest level of lactulose permeability. Although a significant change in lactulose permeability from day 1 to day 2 postinjury could not be demonstrated in the B and EF groups, lactulose permeability in the B+EF group on day 2 postinjury markedly decreased from day 1 but was still significantly higher than that in the sham group. Mannitol permeability was increased in all injured rat groups on day 1 postinjury; on day 2 it remained elevated post-B, decreased post-EF, and further increased after B+EF. Ex vivo measurements of lactulose movements across intestinal epithelial monolayers (IEC-18) were carried out in the presence of blood neutrophils from sham, B, EF, or B+EF rats. We also measured ex vivo transepithelial migration of neutrophils from sham, B, EF, or B+EF rat groups. Neither the transepithelial lactulose movement in the presence of neutrophils from, nor neutrophil migration in, the B or EF rats was significantly different from sham. However, a significant increase in transepithelial lactulose movement and neutrophil migration occurred in the B+EF group. Immunoblot analyses and in situ histochemical localizations of intestinal tight junction proteins, occludin and claudin-3, showed decreases in the distribution of occludin but not claudin-3 in the B, EF, and B+EF groups.

CONCLUSIONS

Alterations in intestinal solute permeability and disruption of tight junction integrity after a two-hit injury with burn and E. faecalis infection, but not after individual injuries of burn or E. faecalis infection, are likely associated with heightened neutrophil flux across the intestinal epithelium.

Biological role of Ep-CAM in the physical interaction between epithelial cells and lymphocytes in intestinal epithelium

The mucosal epithelium including intestinal epithelial cells (IECs) and intraepithelial lymphocytes (IELs) provide a first line of defense in the gastrointestinal tract. However, limited information is currently available concerning the nature of the physical interaction molecule that interconnects IECs and IELs. Among the several monoclonal antibodies (mAbs) generated by immunizing porcine IECs, mAb (5-15-1) was shown to strongly react with IELs in addition to IECs. MALDI-TOF-MS and tandem MS analysis suggested that the antigen belongs to a family of human homophilic epithelial cell adhesion molecule (Ep-CAM). The amino acid sequence of porcine Ep-CAM showed 82.8%, 78.1%, and 76.8% homology compared to human, mouse, and rat Ep-CAM. Moreover, 5-15-1 specifically reacted with transfectant of porcine Ep-CAM. These data suggest that the Ep-CAM may act as a physical homophilic interaction molecule between IELs and IECs at the mucosal epithelium for providing immunological barrier as a first line of defense against mucosal infection.

Barriers built on claudins

The fundamental functions of epithelia and endothelia in multicellular organisms are to separate compositionally distinct compartments and regulate the exchange of small solutes and other substances between them. Tight junctions (TJs) between adjacent cells constitute the barrier to the passage of ions and molecules through the paracellular pathway and function as a 'fence' within the plasma membrane to create and maintain apical and basolateral membrane domains. How TJs achieve this is only beginning to be understood. Recently identified components of TJs include the claudins, a family of four-transmembrane-span proteins that are prime candidates for molecules that function in TJ permeability. Their identification and characterization have provided new insight into the diversity of different TJs and heterogeneity of barrier functions in different epithelia and endothelia.

Expression profiling reveals novel innate and inflammatory responses in the jejunal epithelial compartment during infection with Trichinella spiralis

Infection with intestinal nematodes induces profound pathological changes to the gut that are associated with eventual parasite expulsion. We have applied expression profiling as an initial screening process with oligonucleotide microarrays (Affymetrix MG-U74AV2 gene chips) and time course kinetics to investigate gene transcription triggered by the intraepithelial nematode Trichinella spiralis in jejunal epithelium from BALB/c mice. Of the 4,114 genes detected, 2,617 were present in all uninfected and T. spiralis-infected replicates, 8% of which were notably upregulated, whereas 12% were downregulated at the time of worm expulsion (day 14 postinfection). Upregulation of goblet cell mucin gene transcripts intestinal mucin gene 3 (MUC3), calcium chloride channel 5 (CLCA5), and goblet cell gene 4 (GOB4) is consistent with enhanced production and alteration of mucus, whereas a 60- to 70-fold upregulation of transcripts for mast cell proteases 1 and 2 (MCPT-1 and -2) is consistent with intraepithelial mucosal mast cell recruitment. Importantly, there was novel expression of sialyltransferase 4C (SIAT4C), small proline-rich protein 2A (SPRR2A), and resistin-like molecule beta (RELMbeta) on day 14 postinfection. In contrast, DNase I and regenerating protein 3 (REG3) transcripts were substantially downregulated. Time course analyses revealed early (within 48 h of infection) induction of Siat4c, Sprr2A, and Relmbeta and later (within 120 h) induction of Mcpt-1 and -2. The findings demonstrate early innate responses and later inflammatory changes within the epithelium. The early epithelial responses may be associated both with repair (Sprr2A) and with the development of innate immunity (Siat4c and Relmbeta).

T cells in coxsackievirus-induced myocarditis

Myocarditis is a complex disease in which distinct immunopathogenic mechanisms cause tissue injury. In some but not all cases, autoimmunity is a major pathogenic factor. Cross-reactivity between viral and myosin epitopes underlies both cellular and humoral autoimmunity in myocarditis. Thus, the genetics of the host as well as the virus determine disease pathogenicity. Innate immunity, as represented by gammadelta+ T cells, is important in determining disease susceptibility. The innate effectors rapidly localize in the infected myocardium and through release of IFNgamma (Vgamma4+ cells; BALB/c) or IL-4 (Vgamma1+ cells; C57Bl/6), modulate the developing adaptive immune response to either a Th1 or Th2 response, respectively. The Vgamma4+ cells in BALB/c mice recognize CD1d, a major histocompatibility complex class I-like antigen. The ligand for Vgamma1+ cells is unknown. Only infected myocytes up-regulate CD1d. Signaling through both infection (double stranded RNA) and TNFalpha is required for CD1d up-regulation.

Downregulation of epithelial apoptosis and barrier repair in active Crohn's disease by tumour necrosis factor alpha 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 alpha (TNF-alpha) 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-alpha 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-alpha 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) Omegaxcm(2)) and improved to 34 (3) Omegaxcm(2) after therapy. Occludin, claudin 1, and claudin 4 were not affected by TNF-alpha 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-alpha 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.

Human intestinal microvascular endothelial cells express Toll-like receptor 5: a binding partner for bacterial flagellin

Bacterial flagellin has recently been identified as a ligand for Toll-like receptor 5 (TLR5). Human sites known to specifically express TLR5 include macrophages and gastric and intestinal epithelium. Because infection of intestinal epithelial cells with Salmonella leads to an active transport of flagellin to the subepithelial compartment in proximity to microvessels, we hypothesized that human intestinal endothelial cells functionally express TLR5, thus enabling an active inflammatory response upon binding of translocated flagellin. Endothelial expression of TLR5 in human macro- and microvascular endothelial cells was examined by RT-PCR, immunoblot analysis, and immunofluorescence. Endothelial expression of TLR5 in vivo was verified by immunohistochemistry. Endothelial modulation of ICAM-1 expression was quantitated using flow cytometry, and leukocyte transmigration in vitro was assessed by an endothelial transmigration assay. Epithelial-endothelial cellular interactions upon infection with viable Salmonella were investigated using a coculture system in vitro. We found that Salmonella-infected intestinal epithelial cells induce endothelial ICAM-1 expression in cocultured human endothelial cells. Both macro- (HUVEC) and microvascular endothelial cells derived from human skin (human dermal microvascular endothelial cell 1) and human colon (human intestinal microvascular endothelial cells) were found to express high constitutive amounts of TLR5 mRNA and protein. These findings were paralleled by strong immunoreactivity for TLR5 of normal human colonic microvessels in vivo. Furthermore, incubation of human dermal microvascular endothelial cells with flagellin from clinical isolates of Escherichia and Salmonella strains led to a marked up-regulation of ICAM-1, as well as to an enhanced leukocyte transendothelial cell migration. These results suggest that endothelially expressed TLR5 might play a previously unrecognized role in the innate immune response toward bacterial Ags.

Experimental obstructive jaundice disrupts intestinal mucosal barrier by altering occludin expression: beneficial effect of bombesin and neurotensin

BACKGROUND

Little is known of the molecular events leading to increased intestinal permeability in obstructive jaundice. This study was undertaken to investigate the influence of experimental obstructive jaundice on the expression of the tight junction-associated protein occludin in the intestinal epithelium.

STUDY DESIGN

Seventy male Wistar rats were randomly divided into five groups: I, controls; II, sham-operated; III, bile duct ligation (BDL); IV, BDL+Bombesin (BBS) (30 microg/kg/d); and V, BDL+Neurotensin (NT) (300 microg/kg/d). At the end of the experiment, on day 10, endotoxin was measured in portal and aortic blood. Tissue sections of the terminal ileum were examined histologically and immunohistochemically for evaluation of occludin expression in the intestinal epithelium. Lipid peroxidation and protein oxidation were determined on tissue homogenates from terminal ileum and microbiologic analysis was performed in cecal contents.

RESULTS

Obstructive jaundice resulted in portal and aortic endotoxemia, which was significantly reduced after BBS or NT administration. In the BDL group, there was total loss of occludin expression in numerous enterocytes mainly at the upper third of the villi, while a gradient of positivity existed from crypt to tip. Occludin expression was restored to control state after treatment with BBS or NT. In addition, both peptides reduced intestinal lipid peroxidation, while BBS reduced protein oxidation as well.

CONCLUSIONS

Experimental obstructive jaundice induces regional loss of occludin expression in the intestinal epithelium, which may be a key factor contributing to the disruption of the mucosal barrier. Gut regulatory peptides BBS and NT prevent this alteration, leading to lower portal and systemic endotoxemia.

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 Asp(320) 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.

RhoA, Rac1, and Cdc42 exert distinct effects on epithelial barrier via selective structural and biochemical modulation of junctional proteins and F-actin

Epithelial intercellular junctions regulate cell-cell contact and mucosal barrier function. Both tight junctions (TJs) and adherens junctions (AJs) are regulated in part by their affiliation with the F-actin cytoskeleton. The cytoskeleton in turn is influenced by Rho family small GTPases such as RhoA, Rac1, and Cdc42, all of which constitute eukaryotic targets for several pathogenic organisms. With a tetracycline-repressible system to achieve regulated expression in Madin-Darby canine kidney (MDCK) epithelial cells, we used dominant-negative (DN) and constitutively active (CA) forms of RhoA, Rac1, and Cdc42 as tools to evaluate the precise contribution of each GTPase to epithelial structure and barrier function. All mutant GTPases induced time-dependent disruptions in epithelial gate function and distinct morphological alterations in apical and basal F-actin pools. TJ proteins occludin, ZO-1, claudin-1, claudin-2, and junctional adhesion molecule (JAM)-1 were dramatically redistributed in the presence of CA RhoA or CA Cdc42, whereas only claudins-1 and -2 were redistributed in response to CA Rac1. DN Rac1 expression also induced selective redistribution of claudins-1 and -2 in addition to JAM-1, whereas DN Cdc42 influenced only claudin-2 and DN RhoA had no effect. AJ protein localization was unaffected by any mutant GTPase, but DN Rac1 induced a reduction in E-cadherin detergent solubility. All CA GTPases increased the detergent solubility of claudins-1 and -2, but CA RhoA alone reduced claudin-2 and ZO-1 partitioning to detergent-insoluble membrane rafts. We conclude that Rho family GTPases regulate epithelial intercellular junctions via distinct morphological and biochemical mechanisms and that perturbations in barrier function reflect any imbalance in active/resting GTPase levels rather than simply loss or gain of GTPase activity.

Proinflammatory cytokines disrupt epithelial barrier function by apoptosis-independent mechanisms

It is well known that inflammatory conditions of the intestinal mucosa result in compromised barrier function. Inflammation is characterized by an influx into the mucosa of immune cells that influence epithelial function by releasing proinflammatory cytokines such as IFN-gamma and TNF-alpha. Mucosal barrier function is regulated by the epithelial apical junctional complex (AJC) consisting of the tight junction and the adherens junction. Since the AJC regulates barrier function, we analyzed the influence of IFN-gamma and TNF-alpha on its structure/function and determined the contribution of apoptosis to this process using a model intestinal epithelial cell line, T84, and IFN-gamma and TNF-alpha. AJC structure/function was analyzed by confocal microscopy, biochemical analysis, and physiologic measurement of epithelial gate/fence function. Apoptosis was monitored by determining cytokeratin 18 cleavage and caspase-3 activation. IFN-gamma induced time-dependent disruptions in epithelial gate function that were potentiated by coincubation with TNF-alpha. Tight junction fence function was somewhat disrupted. Cytokine treatment was associated with internalization of AJC transmembrane proteins, junction adhesion molecule 1, occludin, and claudin-1/4 with minimal effects on the cytoplasmic plaque protein zonula occludens 1. Detergent solubility profiles of junction adhesion molecule 1 and E-cadherin and their affiliation with "raft-like" membrane microdomains were modified by these cytokines. Inhibition of cytokine-induced apoptosis did not block induced permeability defects; further emphasizing their primary influence on the epithelial AJC structure and barrier function. Our findings for the first time clearly separate the proapoptotic effects of IFN-gamma and TNF-alpha from their abilities to disrupt barrier function.

A new principle for tight junction modulation based on occludin peptides

The aim of this study was to investigate whether peptides from the extracellular loops of the tight junction protein occludin could be used as a new principle for tight junction modulation. Peptides of 4 to 47 amino acids in length and covering the two extracellular loops of the tight junction protein occludin were synthesized, and their effect on the tight junction permeability in Caco-2 cells was investigated using [14C]mannitol as a para-cellular marker. Lipopeptide derivatives of one of the active occludin peptides (OPs), synthesized by adding a lipoamino acid containing 14 carbon atoms (C14-) to the N terminus of the peptide, were also investigated. Peptides corresponding to the N terminus of the first extracellular loop of occludin increased the permeability of the tight junctions without causing short-term toxicity. However, the peptides had an effect only when added to the basolateral side of the cells, which could be partly explained by degradation by apical peptidases and aggregate formation. By contrast, the lipopeptide C14-OP90-103, which protects the peptide from degradation and aggregation, displayed a rapid apical effect. The l- and d-diastereomers of C14-OP90-103 had distinctly different effects. The d-isomer, which releases intact OP90-103 from the lipoamino acid, displayed a rapid and transient increase in tight junction permeability. The l-isomer, which releases OP90-103 more rapidly, gave a more sustained increase in tight junction permeability. In conclusion, C14-OP90-103 represents a prototype of a new class of tight junction modulators that act on the extracellular domains of tight junction proteins.

Total parenteral nutrition adversely affects gut barrier function in neonatal piglets

Sepsis is the most common morbidity in preterm infants, who often receive total parenteral nutrition (TPN). We hypothesized that gut barrier function is compromised in TPN-fed compared with enterally fed newborn piglets (ENT pigs). Colostrum-deprived newborn pigs were implanted with jugular venous and bladder catheters under general anesthesia. Pigs were either administered TPN (n = 15) or fed formula (ENT pigs, n = 15). After 6 days, pigs were gavaged a solution of mannitol, lactulose, and polyethylene glycol 4000 (PEG 4000) and urine was collected for 24 h. At 7 days, small bowel samples were assayed for myeloperoxidase activity, morphometry, and tight junction protein abundance. Intestinal contents and peripheral organ sites were cultured for bacteria. Urinary recovery (%dose) of mannitol (53 vs. 68) was lower, whereas that of lactulose (2.93 vs. 0.18) and PEG 4000 (12.78 vs. 0.96) were higher in TPN vs. ENT pigs, respectively (P < 0.05). Incidence of translocation was similar in TPN and ENT pigs. Myeloperoxidase activity was increased in TPN vs. ENT pigs in the jejunum (P < 0.001) and was weakly correlated with lactulose (R2 = 0.32) and PEG 4000 (R2 = 0.38) recovery. Goblet cell counts did not change, but intraepithelial lymphocyte numbers decreased with TPN. Only claudin-1 protein abundance was increased in the TPN group. We conclude that TPN is associated with impairment of neonatal gut barrier function as measured by permeability but not translocation.

Regulation of adherens junctions and epithelial paracellular permeability: a novel function for polyamines

Maintenance of intestinal mucosal epithelial integrity requires polyamines that are involved in the multiple signaling pathways controlling gene expression and different epithelial cell functions. Integrity of the intestinal epithelial barrier depends on a complex of proteins composing different intercellular junctions, including tight junctions, adherens junctions, and desmosomes. E-cadherin is primarily found at the adherens junctions and plays a critical role in cell-cell adhesions that are fundamental to formation of the intestinal epithelial barrier. The current study determined whether polyamines regulate intestinal epithelial barrier function by altering E-cadherin expression. Depletion of cellular polyamines by alpha-difluoromethylornithine (DFMO) reduced intracellular free Ca2+ concentration ([Ca2+]cyt), decreased E-cadherin expression, and increased paracellular permeability in normal intestinal epithelial cells (IEC-6 line). Polyamine depletion did not alter expression of tight junction proteins such as zona occludens (ZO)-1, ZO-2, and junctional adhesion molecule (JAM)-1. Addition of exogenous polyamine spermidine reversed the effects of DFMO on [Ca2+]cyt and E-cadherin expression and restored paracellular permeability to near normal. Elevation of [Ca2+]cyt by the Ca2+ ionophore ionomycin increased E-cadherin expression in polyamine-deficient cells. In contrast, reduction of [Ca2+]cyt by polyamine depletion or removal of extracellular Ca2+ not only inhibited expression of E-cadherin mRNA but also decreased the half-life of E-cadherin protein. These results indicate that polyamines regulate intestinal epithelial paracellular barrier function by altering E-cadherin expression and that polyamines are essential for E-cadherin expression at least partially through [Ca2+]cyt.

Neutrophil derived human S100A12 (EN-RAGE) is strongly expressed during chronic active inflammatory bowel disease

BACKGROUND

Intestinal inflammation in Crohn's disease (CD) and ulcerative colitis (UC) is characterised by an influx of neutrophils into the intestinal mucosa. S100A12 is a calcium binding protein with proinflammatory properties. It is secreted by activated neutrophils and interacts with the multiligand receptor for advanced glycation end products (RAGE). Promising anti-inflammatory effects of blocking agents for RAGE have been reported in murine models of colitis.

AIMS

To investigate expression and serum concentrations of S100A12 in inflammatory bowel disease (IBD).

METHODS

We performed immunohistochemical studies and immunofluorescence microscopy in biopsies from patients with CD and UC. S100A12 serum concentrations were analysed using a sandwich ELISA.

RESULTS

Immunohistochemical studies revealed profound expression of S100A12 in inflamed intestinal tissue from IBD patients whereas no expression was found in tissue from healthy controls. Staining for S100A12 during chronic active CD and UC was restricted to infiltrating neutrophils. Serum S100A12 levels were significantly elevated in patients with active CD (470 (125) ng/ml; p<0.001, n=30) as well as those with active UC (400 (120) ng/ml; p<0.01, n=15) compared with healthy controls (75 (15) ng/ml; n=30). Even in inactive disease, elevated serum concentrations were found, at least in CD. S100A12 levels were well correlated with disease activity in CD and UC.

CONCLUSIONS

We demonstrated that neutrophil derived S100A12 is strongly upregulated during chronic active IBD, suggesting an important role during the pathogenesis of IBD. Serum S100A12 may serve as a useful marker for disease activity in patients with IBD.

'In-field' and 'out-of-field' functional impairment during subacute and chronic phases of experimental radiation enteropathy in the rat

PURPOSE

To investigate subacute and chronic functional consequences of localized irradiation of rat small intestine on exposed and shielded segments (proximal and distal).

MATERIALS AND METHODS

The surgical model of a scrotal hernia was used. The ileal loop was exposed to single doses of 18, 21 or 29.6 Gy X-irradiation. Epithelial structure and transport capacity were followed 2 and 26 weeks post-exposure.

RESULTS

Irradiated segments showed mucosal ulceration followed by transmural fibrosis. Transport capacity was impaired from 2 to 26 weeks. Subacute functional impairment was noticed in the proximal segment, without either morphological alteration or neutrophil influx. At 26 weeks, both proximal and distal segments showed impaired epithelial transport capacity, with neutrophil influx in the submucosa in cases of 21-Gy exposure and in the submucosa and muscularis propria after 29.6 Gy.

CONCLUSIONS

Radiation enteritis was characterized by functional impairment, within as well as outside, the irradiation field. During the subacute phase, the irradiated segment may be a source of mediators which might influence intestinal function outside the site of injury via the blood stream and/or enteric nervous system. The development of an intestinal occlusion syndrome during the chronic phase might be responsible for intestinal dysfunction but it does not rule out a possible inflammatory process developing in the shielded parts of the small intestine.

Loss and recovery of the blood-nerve barrier in the rat sciatic nerve after crush injury are associated with expression of intercellular junctional proteins

The blood-nerve barrier in peripheral nerves is important for maintaining the environment for axons. Breakdown of the barrier by nerve injury causes various pathologies. We hypothesized that the breakdown and recovery of the blood-nerve barrier after injury are associated with the changes in the expression of intercellular junctional proteins. To test this hypothesis, we induced crush injuries in the rat sciatic nerve by ligation and analyzed spatiotemporal changes of claudin-1, claudin-5, occludin, VE-cadherin, and connexin43 by immunoconfocal microscopy and morphometry and compared them with changes in the permeability of the blood-nerve barrier by intravenous and local administration of Evans blue-albumin (EBA). On day 1 after removal of the ligature EBA leaked into the connective tissue in the endoneurium and then the leakage gradually decreased and disappeared on day 7. On day 1 claudin-1, claudin-5, occludin, VE-cadherin, and connexin43 had totally disappeared from the perineurium and endoneurium. Thereafter, claudin-1, claudin-5, occludin, and VE-cadherin recovered from day 2, whereas connexin43 was redetected on day 5. These results indicate that the breakdown and following recovery of the blood-nerve barrier are closely associated with changes in the expression of claudins, occludin, VE-cadherin, and connexin43 and that the recovery time course is similar but nonidentical.

Prediction of the oral absorption of low-permeability drugs using small intestine-like 2/4/A1 cell monolayers

PURPOSE

To characterize the paracellular route of 2/4/A1 monolayers and to compare the permeabilities of incompletely absorbed oral drugs in 2/4/A1 with those in Caco-2 monolayers.

METHODS

The cells were cultivated on permeable supports. The 2/4/ A1 expression of genes associated with tight junctions was compared with that in the small intestine using RT-PCR. The aqueous pore radii were determined using paracellular marker molecules. The permeabilities of a series of incompletely absorbed drugs (defined as having a fraction absorbed 0 to 80%) after oral administration to humans were studied.

RESULTS

Occludin and claudin 1 and 3 were expressed in 2/4/A1. The pore radius of 2/4/A1 was 9.0 +/- 0.2 A. which is similar to that in the human small intestine, although the pore radius was smaller (3.7 +/- 0.1 A) in Caco-2. The relationship between permeability and fraction absorbed of 13 drugs was stronger in 2/4/A1 than in Caco-2. The relationships were used to predict the intestinal absorption of another seven drugs. The prediction was more accurate in 2/4/A1 (RMSE = 15.6%) than in Caco-2 (RMSE = 21.1%). Further, Spearman's rank coefficient between FA and permeability was higher in 2/4/A1.

CONCLUSION

The improved 2/4/A1 cell culture model has a more in vivo-like permeability and predicted the oral absorption of incompletely absorbed drugs better than Caco-2 cells.

Protein kinase C modulates pulmonary endothelial permeability: a paradigm for acute lung injury

The intracellular serine/threonine kinase protein kinase C (PKC) has an important role in the genesis of pulmonary edema. This review discusses the PKC-mediated mechanisms that participate in the pulmonary endothelial response to agents involved in lung injury characteristic of the respiratory distress syndrome. Thus the paradigms of PKC-induced lung injury are discussed within the context of pulmonary transvascular fluid exchange. We focus on the signal transduction pathways that are modulated by PKC and their effect on lung endothelial permeability. Specifically, alpha-thrombin, tumor necrosis factor (TNF)-alpha, and reactive oxygen species are discussed because of their well-established roles in both human and experimental lung injury. We conclude that PKC, most likely PKC-alpha, is a primary supporter for lung endothelial injury in response to alpha-thrombin, TNF-alpha, and reactive oxygen species.