NO-dependent and NO-independent IL-1 production by a human colonic epithelial cell line under inflammatory stress

Mechanisms of transport of polymeric and lipidic nanoparticles across the intestinal barrier

Unraveling the mechanisms of nanoparticle transport across the intestinal barrier is essential for designing more efficient nanoparticles for oral administration. The physicochemical parameters of the nanoparticles (e.g., size, surface charge, chemical composition) dictate nanoparticle fate across the intestinal barrier. This review aims to address the most important findings regarding polymeric and lipidic nanoparticle transport across the intestinal barrier, including the evaluation of critical physicochemical parameters of nanoparticles that affect nanocarrier interactions with the intestinal barrier.

Translocator Protein-Mediated Stabilization of Mitochondrial Architecture during Inflammation Stress in Colonic Cells

Chronic inflammation of the gastrointestinal tract increasing the risk of cancer has been described to be linked to the high expression of the mitochondrial translocator protein (18 kDa; TSPO). Accordingly, TSPO drug ligands have been shown to regulate cytokine production and to improve tissue reconstruction. We used HT-29 human colon carcinoma cells to evaluate the role of TSPO and its drug ligands in tumor necrosis factor (TNF)-induced inflammation. TNF-induced interleukin (IL)-8 expression, coupled to reactive oxygen species (ROS) production, was followed by TSPO overexpression. TNF also destabilized mitochondrial ultrastructure, inducing cell death by apoptosis. Treatment with the TSPO drug ligand PK 11195 maintained the mitochondrial ultrastructure, reducing IL-8 and ROS production and cell death. TSPO silencing and overexpression studies demonstrated that the presence of TSPO is essential to control IL-8 and ROS production, so as to maintain mitochondrial ultrastructure and to prevent cell death. Taken together, our data indicate that inflammation results in the disruption of mitochondrial complexes containing TSPO, leading to cell death and epithelia disruption.

SIGNIFICANCE

This work implicates TSPO in the maintenance of mitochondrial membrane integrity and in the control of mitochondrial ROS production, ultimately favoring tissue regeneration.

Immune Homeostasis in Epithelial Cells: Evidence and Role of Inflammasome Signaling Reviewed

The epithelium regulates the interaction between the noxious xenogenous, as well as the microbial environment and the immune system, not only by providing a barrier but also by expressing a number of immunoregulatory membrane receptors, and intracellular danger sensors and their downstream effectors. Amongst these are a number of inflammasome sensor subtypes, which have been initially characterized in myeloid cells and described to be activated upon assembly into multiprotein complexes by microbial and environmental triggers. This review compiles a vast amount of literature that supports a pivotal role for inflammasomes in the various epithelial barriers of the human body as essential factors maintaining immune signaling and homeostasis.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Electron microscope tomography of native membranes

Membrane proteins are often present in low amounts in cells. Their function can be modulated by interactions with other proteins. Moreover, these complexes can be transiently formed, thus making them difficult to be isolated and to be purified. One way to overcome these difficulties is to visualize these complexes in situ in the cells. For such purpose, electron microscopy coupled to tomography is a promising approach that has been developed over the last decades.Mitochondria are a good example of organelles where many membrane proteins form different functional complexes within the outer and the inner membranes. The latter is either close to the former or projects within the matrix to form cristae. Structure of these cristae involves different proteins and can vary from lamellar to tubular forms in normal mitochondria. In pathological conditions, other mitochondrial morphologies have been described, for instance, vesicular structures for inner boundary membrane have been observed.

Unconjugated bilirubin modulates the intestinal epithelial barrier function in a human-derived in vitro model

Unconjugated bilirubin promotes intestinal secretion without affecting nutrient digestion or absorption. In the current study, the effects of unconjugated bilirubin (UCB) on the barrier function of the intestinal epithelium were investigated. The apical side of human intestinal cell line Caco-2 monolayers was challenged with purified UCB. Transepithelial electrical resistance and paracellular fluxes of 10 kD Cascade blue conjugate dextran were measured. Cell monolayer viability was studied using LDH release and trypan blue exclusion tests. Redistribution of enterocyte tight junction occludin was studied by confocal microscopy. Bilirubin induced a dose-dependent decrease of transepithelial electrical resistance (TEER). This effect was maximal at 6 h and tended to be reversed at 48 h. Oxidated bilirubin was ineffective. Bilirubin significantly increased fluorescent dextran paracellular passage. Cell viability was not affected by UCB over the 5-200 nmol/L concentration range. Finally, bilirubin triggered a reversible redistribution of tight junctional occludin. UCB increases the permeability of intestinal epithelium. This effect is reversible, dependent on the redox status of the molecule and the rearrangement of the tight junction. These data attribute to bilirubin a novel role of functional modulator of intestinal paracellular permeability in vitro.

Disaccharides derived from heparin or heparan sulfate regulate IL-8 and IL-1 beta secretion by intestinal epithelial cells

BACKGROUND & AIMS

Intestinal epithelial cells can produce cytokines and chemokines that play an important role in the mucosal immune response. Regulation of this secretion is important to prevent inflammatory tissue damage. Disaccharides derived from heparan sulfate and heparin have been shown to down-regulate inflammation in vivo. We tested the effect of such disaccharides on cytokine secretion by intestinal epithelial cells.

METHODS

Spontaneous and tumor necrosis factor (TNF)-alpha-stimulated interleukin (IL)-8 and IL-1 beta secretion and mRNA expression were assessed in HT-29 and Caco-2 intestinal epithelial cell lines in the presence of a panel of heparin and heparan sulfate disaccharides.

RESULTS

Specific disaccharides suppressed spontaneous and TNF-alpha-induced mediator secretion in a dose-dependent manner. Disaccharide activity was structurally restricted. Preincubation of cells with nonsuppressing disaccharides blocked the activity of suppressing disaccharides. The number of sulfate moieties determined the ability of nonsuppressing disaccharides to block the effect of suppressive disaccharides. No suppression of mRNA expression was noted, and intracellular mediator levels were not reduced.

CONCLUSIONS

Disaccharides derived from heparin and heparan sulfate regulate proinflammatory mediator secretion from intestinal epithelial cells. Dose dependence and competition by structurally diverging disaccharides suggest a receptor-mediated mechanism. Unchanged mRNA and intracellular mediator levels suggest that the disaccharides act at posttranscriptional stages.

Inducible nitric oxide synthase promotes cytokine expression in cardiac allografts but is not required for efficient rejection

BACKGROUND

Inducible nitric oxide synthase (iNOS) is enhanced during acute rejection. Pharmacologic inhibition of nitric oxide synthase (NOS) activity has had variable effects on graft survival in a number of animal models. To further characterize the requirement and effects of iNOS during acute allograft rejection, we examined rejection responses of mice completely deficient of iNOS.

METHODS

Heterotopic cardiac allografts were performed using wild-type and iNOS deficient mice (iNOS[-/-]) as recipients. Graft survival was determined by abdominal palpation. At days 3 and 7 following transplantation, grafts were harvested and analyzed histologically. Cytokine messenger RNA (mRNA) expression was measured by ribonuclease protection assay.

RESULTS

Mean survival time of cardiac allografts did not differ between wild-type (18 +/- 3 days) and iNOS(-/-) recipients (16 +/- 2 days). At 3 days, findings of moderate acute rejection were seen in both recipients groups, although modestly reduced in iNOS(-/ -) mice. By 7 days, allografts in both groups demonstrated severe rejection. Within grafts at day 3, there was a 3-fold reduction in IL-1beta expression and a 4-fold reduction in IL-1RA in iNOS(-/-) recipients (p = 0.03 andp = 0.04, respectively) compared to wild-type recipients. Expression of other proinflammatory cytokines was detected in the grafts from both recipients, but was not significantly different. Finally, rejection responses to iNOS(-/-) cardiac allografts were nearly identical to wild-type allografts.

CONCLUSIONS

Rejection of cardiac allografts by iNOS(-/-) mice occurs in a similar fashion to wild-type recipients, with extensive inflammation and proinflammatory cytokine production. While iNOS may play a role in cytokine induction by macrophages, these studies suggest that iNOS is not required for efficient cardiac graft rejection.

Interleukin 1 and interleukin 1beta converting enzyme (caspase 1) expression in the human colonic epithelial barrier. Caspase 1 downregulation in colon cancer

BACKGROUND

Interleukin (IL) 1beta converting enzyme (now known as caspase 1) is able to process pro-IL-1beta into its active form and is involved in proapoptotic signalling.

AIMS

To characterise IL-1 and caspase 1 expression in human colonic epithelial cells.

METHODS

Intracellular IL-1 content (IL-1alpha and IL-1beta) was measured by ELISA in freshly isolated human normal colonocytes. Caspase 1 expression was determined both at the mRNA level using in situ hybridisation and reverse transcription polymerase chain reaction, and at the protein level by immunoblotting experiments using antibodies specific for the proform of caspase 1 and for its cleavage forms.

RESULTS

Low amounts of IL-1beta were found in nearly all preparations (92%), and IL-1alpha was detected in only 45% of human colonocyte preparations. The normal colonic epithelium strongly expressed caspase 1, both at the mRNA level and at the protein level in its latent form. In contrast, caspase 1 was not expressed in colon cancer (primary colonic adenocarcinomas and cancer cell lines).

CONCLUSIONS

The demonstration that the human colonic epithelial barrier is able to express caspase 1 and its substrate IL-1beta reinforces the concept that, under certain conditions, the epithelium could trigger an inflammatory reaction. In addition, the finding that caspase 1 was downregulated in colonic adenocarcinomas supports the concept that disrupted apoptosis pathways may be involved in tumour formation and/or may confer resistance to treatment.

Listeria monocytogenes stimulates mucus exocytosis in cultured human polarized mucosecreting intestinal cells through action of listeriolysin O

When the intracellular pathogen Listeria monocytogenes infects cultured human mucosecreting polarized HT29-MTX cells apically, it induces the stimulation of mucus exocytosis without cell entry. Using a set of isogenic mutants and purified listeriolysin O (LLO), we identified the L. monocytogenes thiol-activated exotoxin LLO as the agonist of mucus secretion. We demonstrated that the LLO-induced mucus exocytosis did not result from the LLO membrane-damaging activity. We found that LLO-induced mucus exocytosis is an event requiring the binding of LLO to a brush border-associated receptor and membrane oligomerization of the exotoxin. By a pharmacological approach, we demonstrated that no regulatory system or intracellular transducing signal known to be involved in control of mucin exocytosis was activated by LLO. Based on the present data, the stimulatory action of LLO on mucin exocytosis could be accounted for either by an unknown signaling system which remains to be determined or by direct action of LLO with the membrane vesicle components involved in the intracellular vesicular transport of mucins.

Pathophysiological role of nitric oxide in rat experimental colitis

Overproduction of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) may contribute to the pathophysiology of ulcerative colitis. A 2,4,6-trinitrobenzenesulfonic acid sodium salt (TNBS) colitis model was established to examine the effect of selective iNOS inhibition, by S-(2-aminoethyl) isothiouronium bromide (ITU), on colonic mucosal cell damage and inflammation. Rats, killed 7 days after TNBS, had increased colonic mucosal levels of iNOS and interleukin-8 (IL-8), in addition to severe colonic inflammation which was characterized by significantly increased colon weight, damage score and colonic myeloperoxidase activity (MPO) (a marker of neutrophil influx). TNBS-treated rats had markedly decreased body weight and thymus weight. Administration of colitic rats with ITU significantly inhibited iNOS activity/expression and tended to reduce mucosal levels of IL-8, but no effect on MPO activity was observed. Following ITU therapy, colitic rats had reduced colonic damage and losses in body weight and thymus weight were reversed. Improvement of TNBS colitis by ITU suggested that excess NO, produced by iNOS, may have contributed to the initiation/amplification of colonic disease, by mechanisms including enhancement of IL-8 release. NO-mediated enhancement of pro-inflammatory cytokine release was further investigated in vitro. Lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) stimulated release of nitrite, lactate dehydrogenase (LDH), TNF alpha, IL-1 beta and IL-8 from rat peritoneal macrophages, all of which were significantly reduced by ITU. This suggests that NO-mediated cell damage enhances pro-inflammatory mediator release from macrophages. In addition, enhancement of IL-8 and TNF alpha release was also partially NO-dependent in activated peritoneal neutrophils. Therefore, the amelioration of TNBS colitis by ITU could include inhibition of NO-mediated pro-inflammatory cytokine release.