Apoptosis: implications for inflammatory bowel disease

Citric Acid Promoting B Lymphocyte Differentiation and Anti-epithelial Cells Apoptosis Mediate the Protective Effects of Hermetia illucens Feed in ETEC Induced Piglets Diarrhea

Newborn piglets are prone to diarrhea after weaning as a result of changes in their environment and feed. Enterotoxigenic Escherichia coli (ETEC) K88 strain is a typical pathogen that causes diarrhea in such stage of piglets. Hermetia illucens larvae are widely used in livestock and poultry production because of their high nutritional value and immunoregulatory effects. This study aimed to evaluate the protective effects of H. illucens feed in protecting against ETEC induced diarrhea in piglets and to unravel the mechanisms of immune modulation and intestinal barrier maintenance. The results showed that after ETEC infection, citric acid in the serum of the groups fed on H. illucens larvae increased significantly, which stimulated macrophages to secrete cytokines that promote B lymphocyte differentiation, ultimately increasing the production of IgA and IgG in serum. Concomitantly, citric acid also had a positive effect on the intestinal barrier damaged due to ETEC infection by inhibiting the production of inflammatory cytokines, reducing the Bcl-2/Bax ratio, and promoting the expression of tight junction proteins. Correlation analysis showed that the increase of citric acid levels might be related to Massilia. Thus, citric acid derived from H. illucens larvae can improve the immune performance of weaned piglets and reduce ETEC-induced damage to the intestinal barrier in weaned piglets.

Computational drug repositioning of atorvastatin for ulcerative colitis

OBJECTIVE

Ulcerative colitis (UC) is a chronic inflammatory disorder with limited effective therapeutic options for long-term treatment and disease maintenance. We hypothesized that a multi-cohort analysis of independent cohorts representing real-world heterogeneity of UC would identify a robust transcriptomic signature to improve identification of FDA-approved drugs that can be repurposed to treat patients with UC.

MATERIALS AND METHODS

We performed a multi-cohort analysis of 272 colon biopsy transcriptome samples across 11 publicly available datasets to identify a robust UC disease gene signature. We compared the gene signature to in vitro transcriptomic profiles induced by 781 FDA-approved drugs to identify potential drug targets. We used a retrospective cohort study design modeled after a target trial to evaluate the protective effect of predicted drugs on colectomy risk in patients with UC from the Stanford Research Repository (STARR) database and Optum Clinformatics DataMart.

RESULTS

Atorvastatin treatment had the highest inverse-correlation with the UC gene signature among non-oncolytic FDA-approved therapies. In both STARR (n = 827) and Optum (n = 7821), atorvastatin intake was significantly associated with a decreased risk of colectomy, a marker of treatment-refractory disease, compared to patients prescribed a comparator drug (STARR: HR = 0.47, P = .03; Optum: HR = 0.66, P = .03), irrespective of age and length of atorvastatin treatment.

DISCUSSION & CONCLUSION

These findings suggest that atorvastatin may serve as a novel therapeutic option for ameliorating disease in patients with UC. Importantly, we provide a systematic framework for integrating publicly available heterogeneous molecular data with clinical data at a large scale to repurpose existing FDA-approved drugs for a wide range of human diseases.

TNFSF/TNFRSF cytokine gene expression in sickle cell anemia: Up-regulated TNF-like cytokine 1A (TL1A) and its decoy receptor (DcR3) in peripheral blood mononuclear cells and plasma

BACKGROUND

Sickle cell anemia (SCA), a disorder with an important inflammatory component, where vasoocclusion is major contributor to the disease pathophysiology. Pro-inflammatory cytokines play an important regulatory role in the process of inflammation. We investigated the expression TL1A/DR3/DcR3 cytokine signaling pathway in peripheral blood mononuclear cells (PBMC) and their corresponding plasma levels in SCA subjects who presented with acute painful episodes.

MATERIALS AND METHODS

PBMC were isolated from the blood of SCA subjects and normal healthy controls. RNA isolated from PBMC was used for real time gene expression of TL1A/DR3/DcR3. Gene expression was compared in subgroups within SCA subjects with co-inherited fetal hemoglobin (HbF) or alpha-globin gene deletions. Plasma prepared from blood was used for determination of TL1A/DR3/DcR3 proteins by ELISA assays.

RESULTS

In the PBMC of SCA subjects, expression of TL1A and DcR3 is elevated, while DR3 expression is lowered in comparison to normal control PBMC. In SCA subjects with HbF > 10%, TL1A/DcR3 expression is lower, while HbF < 10% is associated with increased TL1A/DcR3 expression. Moreover, subjects with HbF > 10% appear to have significantly fewer pain episodes in comparison to those with HbF < 10%. Deletion of alpha-globin genes appears to have no significant effect on TL1A/DR3/DcR3 expression. Circulating levels of TL1A, DR3 and DcR3 in plasma were significantly elevated in SCA subjects.

CONCLUSIONS

Elevated TL1A and DcR3 expression in PBMC of SCA subjects during painful vasoocclusive crisis, suggest an altered TL1A expression may contribute to the pathophysiology of vasoocclusive crisis in SCA. HbF > 10% appears to moderate TL1A elevation, while HbF < 10% exacerbates TL1A/DcR3 responses. Furthermore, subjects with HbF > 10% have significantly lower pain episodes reported as compared to subjects with HbF < 10%.

Possible Mechanisms of Ethanol-Mediated Colorectal Carcinogenesis: The Role of Cytochrome P4502E1, Etheno-DNA Adducts, and the Anti-Apoptotic Protein Mcl-1

BACKGROUND

Chronic alcohol consumption is a risk factor for colorectal cancer. The mechanisms by which ethanol (EtOH) exerts its carcinogenic effect on the colorectal mucosa are not clear and may include oxidative stress with the action of reactive oxygen species (ROS) generated through EtOH metabolism via cytochrome P4502E1 (CYP2E1) leading to carcinogenic etheno-DNA adducts. ROS may also induce apoptosis. However, the effect of chronic EtOH consumption on CYP2E1, etheno-DNA adducts as well as anti-apoptotic proteins in the colorectal mucosa of heavy drinkers without colorectal inflammation is still not known.

METHODS

Rectal biopsies from 32 alcoholics (>60 g EtOH/d) and from 12 controls (<20 g EtOH/d) were histologically examined, and immunohistochemistry for CYP2E1 and etheno-DNA adducts was performed. Apoptosis (cleaved PARP) as well as anti-apoptotic proteins including Bcl-x_L , Bcl-2, and Mcl-1 were immunohistochemically determined.

RESULTS

No significant difference in mucosal CYP2E1 or etheno-DNA adducts was observed between alcoholics and control patients. However, CYP2E1 and etheno-DNA adducts correlated significantly when both groups were combined (p < 0.001). In addition, although apoptosis was found not to be significantly affected by EtOH, the anti-apoptotic protein Mcl-1, but neither Bcl-x_L nor Bcl-2, was found to be significantly increased in heavy drinkers as compared to controls (p = 0.014).

CONCLUSIONS

Although colorectal CYP2E1 was not found to be significantly increased in alcoholics, CYP2E1 correlated overall with the level of etheno-DNA adducts in the colorectal mucosa, which identifies CYP2E1 as an important factor in colorectal carcinogenesis. Most importantly, however, is the up-regulation of the anti-apoptotic protein Mcl-1 in heavy drinkers counteracting apoptosis and possibly stimulating cancer development.

Cell death at the intestinal epithelial front line

The intestinal epithelium represents the largest epithelial surface in our body. This single-cell-layer epithelium mediates important functions in the absorption of nutrients and in the maintenance of barrier function, preventing luminal microorganisms from invading the body. Due to its constant regeneration the intestinal epithelium is a tissue not only with very high proliferation rates but also with very prominent physiological and pathophysiological cell death induction. The normal physiological differentiation and maturation of intestinal epithelial cells leads to their shedding and apoptotic cell death within a few days, without disturbing the epithelial barrier integrity. In contrast excessive intestinal epithelial cell death induced by irradiation, drugs and inflammation severely impairs the vital functions of this tissue. In this review we discuss cell death processes in the intestinal epithelium in health and disease, with special emphasis on cell death triggered by the tumour necrosis factor receptor family.

A limited role of p53 on the ability of a Hexane fraction of American ginseng to suppress mouse colitis

Ulcerative colitis (UC) is debilitating and carries a high colon cancer risk. Apoptosis of inflammatory cells is a key mechanism regulating UC. We have recently shown that American ginseng (AG), and to a greater extent, a Hexane fraction of AG (HAG) can cause apoptosis and suppress mouse colitis through a p53-mediated mechanism. Here, we tested the hypothesis that HAG suppresses colitis through a p53 mechanism. We found only a limited impact of p53 in the ability of HAG to induce inflammatory cell apoptosis and suppress mouse colitis in vitro and in vivo. Finally, we asked whether HAG could cause cell cycle arrest of HCT116 colon cancer cells in vitro. Interestingly, HAG caused a G1 arrest of such cells independent of p53 status. Findings are significant because HAG suppresses colitis and associated colon cancer, and mutation in p53 is observed in most colitis-driven colon cancers. Therefore, HAG might be very effective in targeting the inflammatory cells and cancer cells since it induces apoptosis of inflammatory cells and cell cycle arrest in both p53^−/− and WT p53 colon cancer cells.

Exercise Training Reduces Inflammatory Mediators in the Intestinal Tract of Healthy Older Adult Mice

Le vieillissement s’allie à une augmentation d’inflammation intestinale et le risque élevé de maladies chroniques, y compris les maladies inflammatoires de l’intestin et le cancer du côlon; nombreuses études épidémiologiques indiquent que l’exercice régulier réduit les risques. Cette étude a examiné les effets à long terme de l’exercice volontaire sur les médiateurs inflammatoires dans les intestins des souris âgées et en bonne santé C57BL/6 (âgées de 15–16 mois). On a désigné les animaux soit à quatre mois de roue d’exercice à souris (RES ; n – 20), soit à une groupe de contrôle « sédentaire » (NRL ; n = 20). Les lymphocytes intestinaux ont été récoltés et analysés pour la présence de (1) pro-inflammatoire (TNF-a, IL-1β) et de cytokines pléotropes (IL-6), et (2) de pro-(caspase-3/-7) et d’anti-(Bcl-2) protéines apoptotiques. L’efficacité d’exercise a été confirmée par l’activité des enzymes dans les muscles squelettiques ; l’évidence de stress a été confirmée par un plasma 8-iso-PGF2α et la corticostérone. Les RES souris ont réalisés une incidence inférieure de TNF-α, de la caspase-7, et de 8-isoprostanes (p < .05) par rapport aux contrôles sédentaires, ce qui suggère que l’exercice à long terme peut « protéger » l’intestin en réduisant la manifestation de cytokines inflammatoires et du protéine apoptotique.

Regeneration associated growth factor receptor and epithelial marker expression in lymphoid aggregates of ulcerative colitis

OBJECTIVE

Mesenchymal-epithelial transition may have crucial role in mucosal regeneration, hence we assayed epithelial growth factor receptor (EGFR), insulin-like growth factor receptor-1 (IGF1R), hepatocyte-derived growth factor receptor (HGFR), CDX2 and cytokeratin (CK) expression in lymphoid aggregates (LA) of ulcerative colitis (UC).

MATERIAL AND METHODS

Tissue microarrays (TMAs) made of biopsy samples from 20 mildly, 20 moderately and 20 severely active UC, 12 non-specific colitis (NSC) and 20 healthy colon were prepared, and immunolabelled with anti-EGFR, -IGF1R, -HGFR, -CDX2, -CK antibodies. After virtual microscopic evaluation, one-way ANOVA and correlation analysis were performed. For validation, TaqMan real-time RT-PCR was performed by using RNA from laser microdissected LA from 10 healthy colon and 10 endoscopically active UC biopsies.

RESULTS

The number of LA was in tight positive correlation with the severity of inflammation (r=0.9). The number of EGFR/HGFR positive subepithelial cells was found to be significantly elevated in severe (21.6+/-2.1%/21.3+/-1.9%), moderate (14.3+/-1.7%/14.6+/-1.6%) and mild (7.2+/-1.6%/7.4+/-1.3%) inflammation compared to healthy colon mucosa (2.6+/-1.4%/2.4+/-1.03%) (p < 0.005). Some alterations were found between UC and NSC samples regarding EGFR and HGFR expression. IGF1R immunoreactive cells were only found in a trace number in all cases. Increasing trend of CDX2 and CK positive subepithelial cells was found in active UC, but it was not in significant correlation with the severity of inflammation.

CONCLUSION

EGFR and HGFR positive subepithelial cells in LA may be involved in the induction of the regenerative mucosal processes. The presence of CDX2/CK positive subepithelial cells suggests that mesenchymal-to-epithelial transition may be located to lymphoid aggregates.

GREEN TEA POLYPHENOLS MEDIATED APOPTOSIS IN INTESTINAL EPITHELIAL CELLS BY A FADD-DEPENDENT PATHWAY

Colorectal cancer is the most common malignant complication in patients with chronic inflammatory bowel disease (IBD). In addition, these patients are at risk for developing painful complications during chemotherapy due to cytotoxic effects of drugs currently in use. Past studies have suggested a protective effect of tea consumption on gastrointestinal (GI) malignancies. Green tea polyphenols (GrTP) inhibited carcinogen-induced GI tumors in rodents and induced apoptosis in various carcinoma cell lines. We hypothesized that GrTP and its polyphenolic compounds regulate apoptosis in the intestinal epithelia. In this study, the effects of GrTP and its polyphenolics on apoptosis was evaluated in intestinal epithelial, IEC-6, cells grown to 85% confluency. GrTP (400-800 mg/ml) induced DNA fragmentation in a dose dependent fashion. Higher concentrations (>800 mg/ml) induced a mixed apoptosis and cytolysis. Epithelial cells exposed to GrTP and a major polyphenol, EGCG, but not EGC or EC, increased caspase activities in a time and dose dependent manner. The caspase inhibitors rescued cells from GrTP and EGCG-induced cell death. Concomitantly, GrTP resulted in activation of fatty acid synthase (Fas)-associated protein with death domain (FADD) and recruitment to Fas/CD95 domain 30 minutes following treatment. While GrTP also blocked NF-κB activation, an NFκ-B inhibitor (MG132) only promoted cytolysis. In conclusion, these data demonstrated GrTP and EGCG induced apoptosis in intestinal epithelia mediated by caspase-8 through a FADD dependent pathway. Future investigation may warrant preventive as well as therapeutic strategies for GrTP in GI malignancy.

Enterobacter sakazakii enhances epithelial cell injury by inducing apoptosis in a rat model of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disorder that affects 2%-5% of all premature infants. Enterobacter sakazakii, a common contaminant of milk-based powdered infant formula, has been implicated as a causative agent of sepsis, meningitis, and NEC in newborn infants, with high mortality rates. However, the role played by E. sakazakii in the pathogenesis of NEC is, to date, not known. Here, we demonstrate for the first time that E. sakazakii can induce clinical and histological NEC in newborn rats. E. sakazakii was found to bind to enterocytes in rat pups at the tips of villi and to intestinal epithelial cells (IEC-6) in culture, with no significant invasion. Exposure to E. sakazakii induced apoptosis and increased the production of interleukin-6 in IEC-6 cells and in the animal model. These data suggest that E. sakazakii could be a potential pathogen that induces NEC and triggers intestinal disease by modulating enterocyte intracellular signaling pathways.

Elevated insulin-like growth factor 1 receptor, hepatocyte growth factor receptor and telomerase protein expression in mild ulcerative colitis

OBJECTIVE

The risk of development of colorectal carcinoma is elevated in chronic, long-standing ulcerative colitis (UC). The changes in regenerative and immortalizing pathways caused by the inflammatory process, and that have been proved to be carcinogenic in other human tissues, have not been fully and uniformly described. We assayed the expression alterations of regenerative signal receptors and cell-aging inhibitory systems within colonic crypts by considering the histological activity of the disease.

METHODS

I-type insulin-like growth factor receptor (IGF1R), hepatocyte growth factor receptor (HGFR), telomerase reverse transcriptase (TERT) and telomerase associated protein (TP-1) expression were evaluated immunohistochemically on biopsy specimens from 11 mild, 11 moderate and 12 severe active inflammation of UC cases and from 10 normal colonic tissue cases. Independent colonic biopsies from 5 healthy and 7 severe UC cases were used for TaqMan real-time RT-PCR validation.

RESULTS

In mild inflammation, all observed parameters showed significantly elevated epithelial protein expression (IGF1R: 22.3 +/- 9.46%; HGFR: 35.3 +/- 22.8%; TERT/TP-1: 2.1 +/- 1.87%/2 +/- 1.32%) compared to normal (p < 0.005). In moderately active inflammation, only IGF1R expression was significantly higher (50.2 +/- 8.6%) compared to normal and mild inflammation (p < 0.005). In severe inflammation, all parameters showed decreased epithelial expression; IGF1R showed decreased mRNA expression, while HGFR was overexpressed and TERT showed a decreased tendency.

CONCLUSIONS

The epithelial expression of IGF1R, HGFR and TERT/TP-1 is elevated in mildly active UC. This phenomenon may allow the epithelial cells that collected genetic defects during severe inflammatory episodes pathologically to survive and proliferate.

Effect of taurine on oxidative stress and apoptosis-related protein expression in trinitrobenzene sulphonic acid-induced colitis

Ulcerative colitis (UC) is a multi-factorial inflammatory disease of the colon and rectum. The present study was undertaken to investigate the effect of taurine, an anti-oxidant amino acid, on oxidative stress and the expression of apoptosis-related proteins, pro-apoptotic Bax and anti-apoptotic B cell lymphoma-2 (Bcl-2) in colon tissue in rats with 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis. Rats received taurine (1.5% w/v) in drinking water for 15 days before and 15 days after administration of TNBS solution. Then, colonic myeloperoxidase (MPO) activity, malondialdehyde (MDA) and glutathione (GSH) levels, and Bax and Bcl-2 expression were measured. TNBS-induced colitis caused significantly increased MPO activity and MDA levels and decreased GSH levels in colon tissue compared to controls. Increase in Bax expression and decrease in Bcl-2 expression were detected in colon of rats with TNBS-induced colitis. Taurine treatment was associated with amelioration in macroscopic and microscopic colitis scores, decreased colonic MPO activity and MDA levels and increased GSH levels in TNBS-induced colitis. In addition, taurine reduced the expression of Bax and prevented the loss of Bcl-2 proteins in colon tissue of rats with TNBS-induced colitis. The results of this study show that taurine administration may exert beneficial effects in UC by decreasing inflammatory reactions, oxidative stress and apoptosis.

Expression profiling of apoptosis-related genes in enterocytes isolated from patients with ulcerative colitis

Apoptosis regulation has been implicated as a main cause of epithelial dysfunction in patients with ulcerative colitis. Apoptosis can be divided into distinct pathways, which depend on the expression of a large number of apoptosis-related genes. The aim was to elucidate which pathways are dominant in normal and inflamed colonic epithelial cells. An apoptosis-specific gene array expression profiling system of 96 genes was used to determine the expression profile of apoptosis-related genes. Epithelial cells isolated from three patients with active ulcerative colitis were pooled and compared to pooled epithelial cells isolated from three control subjects. Genes found to be three-fold or more overexpressed in ulcerative colitis were subsequently analysed by PCR in a larger population (10 patients with ulcerative colitis, 8 control subjects). Selected genes found not to be regulated were additionally tested by PCR in the same population. Six genes were found to be highly expressed in epithelial cells from both controls and ulcerative colitis patients. These included Bcl-2 antagonist/killer, B lymphoid tyrosine kinase, caspase 14, Harakiri, tumour necrosis factor (TNF) receptor 2, and TNF receptor-associated factor 1 (TRAF1). Three genes were found to be upregulated in ulcerative colitis (p<0.01): caspase 1 and 5, and inhibitor of apoptosis protein 2 (c-IAP2). Both receptor- and mitochondrion-dependent apoptosis pathways are well expressed in enterocytes. Mainly activation-dependent and cytoprotective genes were upregulated in ulcerative colitis.

Attenuation of apoptosis in enterocytes by blockade of potassium channels

Apoptosis plays an important role in maintaining the balance between proliferation and cell loss in the intestinal epithelium. Apoptosis rates may increase in intestinal pathologies such as inflammatory bowel disease and necrotizing enterocolitis, suggesting pharmacological prevention of apoptosis as a therapy for these conditions. Here, we explore the feasibility of this approach using the rat epithelial cell line IEC-6 as a model. On the basis of the known role of K+ efflux in apoptosis in various cell types, we hypothesized that K+ efflux is essential for apoptosis in enterocytes and that pharmacological blockade of this efflux would inhibit apoptosis. By probing intracellular [K+] with the K+-sensitive fluorescent dye and measuring the efflux of 86Rb+, we found that apoptosis-inducing treatment with the proteasome inhibitor MG-132 leads to a twofold increase in K+ efflux from IEC-6 cells. Blockade of K+ efflux with tetraethylammonium, 4-aminopyridine, stromatoxin, chromanol 293B, and the recently described K+ channel inhibitor 48F10 prevents DNA fragmentation, caspase activation, release of cytochrome c from mitochondria, and loss of mitochondrial membrane potential. Thus K+ efflux occurs early in the apoptotic program and is required for the execution of later events. Apoptotic K+ efflux critically depends on activation of p38 MAPK. These results demonstrate for the first time the requirement of K+ channel-mediated K+ efflux for progression of apoptosis in enterocytes and suggest the use of K+ channel blockers to prevent apoptotic cell loss occurring in intestinal pathologies.

Growth in epithelial cell proliferation and apoptosis correlates specifically to the inflammation activity of inflammatory bowel diseases: ulcerative colitis shows specific p53- and EGFR expression alterations

PURPOSE

Epithelial cell turnover related differences between ulcerative colitis, Crohn's colitis, and aspecific colitis are not known yet.

METHODS

Totally 345 formalin-fixed, paraffin-embedded biopsy specimens from 33 ulcerative colitis, 26 Crohn's colitis, 30 aspecific colitis, and 10 healthy patients were observed with the TdT-mediated dUTP nick end labeling method and proliferating cell nuclear antigen-, p53-, and epithelial growth factor receptor immunohistochemistry. Because of epithelial growth factor receptor positivity of subepithelial cells epithelial growth factor receptor and CD45, CD68, or CD83 double fluorescence immunohistochemistry were performed on 16 freshly frozen samples from 8 severely active ulcerative colitis and 8 severely active Crohn's colitis patients to describe lamina propria's mononuclear cells, respectively.

RESULTS

The epithelial growth factor receptor expression was significantly lower in each inflammatory group compared with normal (P < 0.005) and decreased significantly in mild ulcerative colitis compared with mild Crohn's colitis or aspecific colitis (P < 0.005). Numerous epithelial growth factor receptor and CD45 double-positive submucosal mononuclear cells were observed in moderate-severe inflammations. The p53-expression was significantly higher in each inflammatory group compared with normal (P < 0.05). Significant differences were found between mildly, moderately, and severely inflamed samples in ulcerative colitis (P < 0.05) compared with Crohn's colitis or aspecific colitis. Apoptotic/proliferative rates increased significantly in line with the inflammatory process (P < 0.0001/0.05), but the TdT-mediated dUTP nick end labeling and proliferating cell nuclear antigen-labeling characteristics did not show disease type specificity.

CONCLUSIONS

Based on our results, the alterations of epithelial growth factor receptor and p53 expression show ulcerative colitis specificity, whereas the rate of epithelial apoptosis and proliferation are determined by the histologic activity of the inflammation. The increased epithelial growth factor receptor expression by the lamina propria's mononuclear cells in inflammation may suggest its role as an autoantigen.

Antigen transport and cytoskeletal characteristics of a distinct enterocyte population in inflammatory bowel diseases

Intestinal antigen uptake is enhanced in inflammatory bowel disease. We analyzed transcellular transport routes of antigens in different compartments of normal enterocytes and atypical intestinal epithelial cells called "rapid antigen uptake into the cytosol enterocytes" (RACE cells). These cells constitute a recently described population of enterocyte-derived cells, which are increased in inflammatory bowel disease. Mucosa of freshly resected specimens were incubated with the antigens ovalbumin or horseradish peroxidase. Ultrastructural labeling patterns of differentiation-dependent proteins, the brush-border enzyme sucrase-isomaltase and the cytoskeleton proteins villin and actin, were determined in enterocytes. Apoptosis was investigated biochemically and ultrastructurally by cleavage of caspase-3. Both antigens were transported to late endosomes and to trans-Golgi vesicles of enterocytes in inflammatory bowel disease and control specimens. Quantitative evaluation revealed a significantly increased transepithelial antigen transport in both compartments of RACE relative to normal enterocytes. Labeling densities for sucrase-isomaltase, villin, and actin were decreased in RACE relative to normal enterocytes. Caspase-3 was not increased in RACE cells relative to controls. RACE cells are characterized by increased antigen transport to late endosomes and the trans-Golgi network, a disassembled cytoskeleton and lower concentrations of proteins that are markers of cell differentiation.

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.

Review article: oxidative stress as a pathogenic factor in inflammatory bowel disease--radicals or ridiculous?

Virtually all inflammatory mediators investigated to date seem to be dysregulated in the inflamed intestinal mucosa of patients with inflammatory bowel disease. However, which of these are actually involved in the initiation and perpetuation of intestinal tissue damage is still not fully understood. Amongst these mediators are the reactive oxygen metabolites, produced in large amounts by the massively infiltrating leucocytes. These reactive oxygen metabolites are believed to constitute a major tissue-destructive force and may contribute significantly to the pathogenesis of inflammatory bowel disease. This paper provides a concise overview of reactive oxygen metabolite biochemistry, the types of cell and tissue damage potentially inflicted by them, and the endogenous antioxidants which should prevent these harmful effects. An up-to-date summary of the available human experimental data suggests that reactive oxygen metabolite-mediated injury is important in both the primary and downstream secondary pathophysiological mechanisms underlying intestinal inflammation. Nonetheless, how the individual components of the mucosal antioxidant enzymatic cascade respond to inflammatory conditions is a neglected area of research. This particular aspect of intestinal mucosal oxidative stress therefore merits further study, in order to provide a sound, scientific basis for the design of antioxidant-directed treatment strategies for inflammatory bowel disease patients.

Expression, preparation, and high-throughput screening of caspase-8: discovery of redox-based and steroid diacid inhibition

Because of the intimate role of caspase-8 in apoptosis signaling pathways from FAS, TNFR1, and other death receptors, the enzyme is a potentially important therapeutic target. We have generated an Escherichia coli expression construct for caspase-8 in which a His-tag sequence is inserted ahead of codon 217 of caspase-8. The strain produced a significant amount of soluble His-tagged 31-kDa inactive single-chain enzyme precursor. This 31-kDa protein could be purified to 98% purity. Hydroxyapatite resolved the enzyme into two species, one with the appropriate 31,090 relative mass and the other with 178 units additional mass. The latter proved to result from E. coli-based modification of the His-tag with one equivalent of glucono-1,5-lactone. The purified proteins could be activated by autoproteolysis to the appropriate 19- plus 11-kDa enzyme by the addition of dithiothreitol in appropriate buffer conditions. This yielded an enzyme with specific activity of 4-5 units/mg against 200 microM Ac-IETD-pNA at 25 degrees C. The fully active protein was used in a high-throughput screen for inhibitors of caspase-8. A preliminary robustness screen demonstrated that caspase-8 is susceptible to reactive oxygen-based inactivation in the presence of dithiothreitol (DTT) but not in the presence of cysteine. Investigation into the mechanism of this inactivation showed that quinone-like compounds were reduced by DTT establishing a reactive oxygen generating redox cycle the products of which (likely H(2)O(2)) inactivated the enzyme. A new class of caspase-8 inhibitors, steroid-derived diacids, with affinity in the low micromolar range were discovered in the refined screen. Structure--activity investigation of the inhibitors showed that both the steroid template and the acid moieties were required for activity.

Epithelial barrier defects in ulcerative colitis: characterization and quantification by electrophysiological imaging

BACKGROUND & AIMS

In ulcerative colitis (UC), the epithelial barrier is impaired by erosion/ulcer-type lesions and epithelial apoptosis causing local leaks, and generalized tight junction alterations increasing the basal permeability. We quantified the contribution of these mechanisms to the increased colonic ion permeability.

METHODS

Sigmoid colon was stripped, and the spatial distribution of current clamped across the viable epithelium was recorded by a microelectrode probe, using the conductance scanning method. Local leaks (circumscribed conductive peaks) were marked, and structural changes were studied in H&E-stained series sections.

RESULTS

Overall conductivity increased from 8.4 +/- 0.7 mS/cm(2) (mean +/- SEM) in controls to 11.7 +/- 0.6 in specimens with mild inflammation (i.e., with intact epithelium) and 34.4 +/- 6.2 mS/cm(2) in moderate-to-severe inflammation (i.e., with visible epithelial lesions). Only in part this was caused by a generalized increase in basal conductivity (12.2 +/- 1.5 mS/cm(2) in moderate-to-severe UC vs. 8.3 +/- 0.7 in controls). More importantly, the spatial distribution of conductivity, which was even in controls, showed dramatic leaks in UC. Leaks found in mild inflammation without epithelial lesion turned out to be foci of epithelial apoptosis. In moderate-to-severe inflammation, leaks correlated with epithelial erosion/ulcer-type lesions or crypt abscesses.

CONCLUSIONS

In early UC, but not in controls, seemingly intact epithelium comprises leaks at apoptotic foci. With more intensive inflammation, erosion/ulcer-type lesions are highly conductive, even if covered with fibrin. Local leaks contribute 19% to the overall epithelial conductivity in mild and 65% in moderate-to-severe inflammation.

Lipoxin A(4) and aspirin-triggered 15-epi-lipoxin A(4) antagonize TNF-alpha-stimulated neutrophil-enterocyte interactions in vitro and attenuate TNF-alpha-induced chemokine release and colonocyte apoptosis in human intestinal mucosa ex vivo

Lipoxins (LXs) are lipoxygenase-derived eicosanoids and putative endogenous braking signals for inflammation in the gastrointestinal tract and other organs. Aspirin triggers the production of 15-epimers during cell-cell interaction in a cytokine-primed milieu, and aspirin-triggered 15-epi-5(S),6(R),15(S)-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (15-epi-LXA(4)) may contribute to the bioactivity profile of this prototype nonsteroidal anti-inflammatory drug in vivo. We determined the effect of LXA(4), 15-(R/S)-methyl-11,12-dehydro-LXA(4) methyl ester (15-(R/S)-methyl-LXA(4)), and stable analogs of LXA(4) on TNF-alpha-stimulated neutrophil-enterocyte interaction in vitro and TNF-alpha-stimulated chemokine release, changes in mucosal architecture, and enterocyte apoptosis in cytokine-activated intact human colonic mucosa ex vivo. LXA(4), 15-(R/S)-epi-LXA(4), and 16-phenoxy-11,12-dehydro-17,18,19,20-tetranor-LXA(4) methyl ester (16-phenoxy-LXA(4)) inhibited TNF-alpha-stimulated neutrophil adherence to epithelial monolayers at nanomolar concentrations. In parallel experiments involving human colonic mucosa ex vivo, LXA(4)potently attenuated TNF-alpha-stimulated release of the C-X-C chemokine IL-8, and the C-C chemokines monocyte-chemoattractant protein-1 (MCP-1) and RANTES. Exposure of strips of normal human colonic mucosa to TNF-alpha induced disruption of mucosa architecture and enhanced colonocyte apoptosis via a caspase-3-independent mechanism. Prior exposure of the mucosa strips to 15-(R/S)-methyl-LXA(4) attenuated TNF-alpha-stimulated colonocyte apoptosis and protected the mucosa against TNF-alpha-induced mucosal damage. In aggregate, our data demonstrate that lipoxins and aspirin-triggered 15-epi-LXA(4) are potent antagonists of TNF-alpha-mediated neutrophil-enterocyte interactions in vitro, attenuate TNF-alpha-triggered chemokine release and colonocyte apoptosis, and are protective against TNF-alpha-induced morphological disruption in human colonic strips ex vivo. Our observations further expand the anti-inflammatory profile of these lipoxygenase-derived eicosanoids and suggest new therapeutic approaches for the treatment of inflammatory bowel disease.