Short-term effects of Poly(I: C) on gut permeability. Pharmacol Res. 2015;101:130-136. [PMID: 26145280 DOI: 10.1016/j.phrs.2015.06.016]

Miniature chicken ileal explant culture to investigate the inflammatory response induced by pathogen-associated molecular patterns

Gastrointestinal inflammation leads to maldigestion and systemic diseases in poultry. To tackle the problem of the industry and to search for therapeutic candidates in vitro models are inevitable. Both immersion and air-liquid interface explant models are available, although there is limited information on the size-dependent applicability and response to different pathogen-associated molecular patterns (PAMPs) in the case of these model systems. The study aimed to compare the morphology and viability of miniature chicken gut explant cultures obtained with a biopsy punch to examine the size-dependent change over time. To verify the applicability of the model, pathogen-associated molecular patterns (PAMPs): flagellin, lipoteichoic acid (LTA) and polyinosinic polycytidylic acid (poly I:C) were applied to induce inflammation. The 2 mm diameter explants showed a decrease in metabolic activity measured by CCK-8 assay after 12 h and a significantly higher extracellular lactate dehydrogenase activity indicating cellular damage compared to the 1 mm explants, supported by histological differences after 24 h of culturing. After 12 h of incubation, the 1.5 mm explants retained columnar epithelial lining with moderate damage of the lamina propria (H&E and pan-cytokeratin staining). Exposure to 100 μg/mL poly I:C reduced the metabolic activity of the 1.5 mm explants. LTA and poly I:C increased IFN-γ concentration at both applied doses and IFN-α concentration was elevated by 50 μg/mL poly I:C treatment. Flagellin administration raised IL-2, IL-6, and RANTES levels, while higher LTA and poly I:C concentrations increased the IFN-γ/IL-10 ratio. According to the observations, the viability and integrity of the explants decreases with their size. After 12 h, the 1.5 mm diameter miniature chicken ileal explant stimulated with PAMPs can be an appropriate model to mimic diseases involving tissue damage and inflammation.

The Pivotal Role of Microbiota in Modulating the Neuronal-Glial-Epithelial Unit

The enteric nervous system (ENS) consists of enteric neurons and enteric glial cells (EGCs) and controls the function of the epithelial barrier. Thus, a novel concept of neuronal-glial-epithelial unit in the gut was put forward by analogy with neuronal-glial-endothelial unit in the brain. The environment in the gastrointestinal (GI) tract is complex as it harbours millions of bacteria, which extensively attach with intestinal epithelium. The cross-talk between the neuronal-glial-endothelial unit and microbiota plays a pivotal role in modulating the epithelial barrier's permeability, intestinal development and immune response. And evidence shows dysbiosis is the potent risk factor in the pathologic process of Parkinson's disease (PD) and inflammatory bowel disease (IBD). In this review, we summarize the compelling results in favor of microbiota serving as the key modulator in the neuronal-glial-epithelial unit development and function, with profound effects on intestinal homeostasis.

LRRC19 Promotes Permeability of the Gut Epithelial Barrier Through Degrading PKC-ζ and PKCι/λ to Reduce Expression of ZO1, ZO3, and Occludin

BACKGROUND

A dysfunctional gut epithelial barrier allows the augmented permeation of endotoxins, luminal antigens, and bacteria into the bloodstream, causing disease. The maintenance of gut epithelial barrier integrity may be regulated by multiple factors. Herein we analyze the role of leucine-rich repeat-containing protein 19 (LRRC19) in regulating the permeability of the gut epithelial barrier.

METHODS

We utilized Lrrc19 knockout (KO) mice and clinical samples through transmission electron, intestinal permeability assay, Western blot, and immunofluorescence staining to characterize the role of LRRC19 in the permeability of the gut epithelial barrier.

RESULTS

We found that LRRC19, which is expressed in gut epithelial cells, impairs gut barrier function. Transmission electron micrographs revealed a tighter junction and narrower gaps in the colon epithelium cells in LRRC19 KO mice. There were lower levels of serum lipopolysaccharide and 4 kDa-fluorescein isothiocyanate-dextran after gavage in LRRC19 KO mice than in wild-type mice. We found that LRRC19 could reduce the expression of zonula occludens (ZO)-1, ZO-3, and occludin in the colonic epithelial cells. The decreased expression of ZO-1, ZO-3, and occludin was dependent on degrading protein kinase C (PKC) ζ and PKCι/λ through K48 ubiquitination by LRRC19. The expression of LRRC19 was also negatively correlated with ZO-1, ZO-3, occludin, PKCζ, and PKCι/λ in human colorectal cancers.

CONCLUSIONS

The protein LRRC19 can promote the permeability of the gut epithelial barrier through degrading PKC ζ and PKCι/λ to reduce the expression of ZO-1, ZO-3, and occludin.

Gut Susceptibility to Viral Invasion: Contributing Roles of Diet, Microbiota and Enteric Nervous System to Mucosal Barrier Preservation

The gastrointestinal lumen is a rich source of eukaryotic and prokaryotic viruses which, together with bacteria, fungi and other microorganisms comprise the gut microbiota. Pathogenic viruses inhabiting this niche have the potential to induce local as well as systemic complications; among them, the viral ability to disrupt the mucosal barrier is one mechanism associated with the promotion of diarrhea and tissue invasion. This review gathers recent evidence showing the contributing effects of diet, gut microbiota and the enteric nervous system to either support or impair the mucosal barrier in the context of viral attack.

Sertraline and Citalopram Actions on Gut Barrier Function

INTRODUCTION

Disruption of intestinal barrier is a key component to various diseases. Whether barrier dysfunction is the cause or effect in these situations is still unknown, although it is believed that translocation of luminal content may initiate gastrointestinal or systemic inflammatory disorders. Since trauma- or infection-driven epithelial permeability depends on Toll-like receptor (TLR) activity, inhibition of TLR signaling has been proposed as a strategy to protect intestinal barrier integrity after infection or other pathological conditions. Recently, selective serotonin recapture inhibitors including sertraline and citalopram were shown to inhibit TLR-3 activity, but the direct effects of these antidepressant drugs on the gut mucosa barrier remain largely unexplored.

MATERIALS AND METHODS

To investigate this, two approaches were used: first, ex vivo studies were performed to evaluate sertraline and citalopram-driven changes in permeability in isolated intestinal tissue. Second, both compounds were tested for their preventive effects in a rat model of disrupted gut barrier, induced by a low protein (LP) diet.

RESULTS

Only sertraline was able to increase transepithelial electrical resistance in the rat colon both when used in an ex vivo (0.8 μg/mL, 180 min) or in vivo (30 mg/kg p.o., 20 days) fashion. However, citalopram (20 mg/kg p.o., 20 days), but not sertraline, prevented the increase in phospho-IRF3 protein, a marker of TLR-3 activation, in LP-rat ileum. Neither antidepressant affected locomotion, anxiety-like behaviours or stress-induced defecation.

CONCLUSION

Our data provides evidence to support the investigation of sertraline as therapeutic strategy to protect intestinal barrier function under life-threatening situations or chronic conditions associated with gut epithelial disruption.

Investigating Gut Permeability in Animal Models of Disease

A growing number of investigations report the association between gut permeability and intestinal or extra-intestinal disorders under the basis that translocation of gut luminal contents could affect tissue function, either directly or indirectly. Still, in many cases it is unknown whether disruption of the gut barrier is a causative agent or a consequence of these conditions. Adequate experimental models are therefore required to further understand the pathophysiology of health disorders associated to gut barrier disruption and to develop and test pharmacological treatments. Here, we review the current animal models that display enhanced intestinal permeability, and discuss (1) their suitability to address mechanistic questions, such as the association between gut barrier alterations and disease and (2) their validity to test potential treatments for pathologies that are characterized by enhanced intestinal permeability.

Novel ex Vivo Experimental Setup to Assay the Vectorial Transepithelial Enteroendocrine Secretions of Different Intestinal Segments

The enteroendocrine system coordinates gastrointestinal (GI) tract functionality and the whole organism. However, the scarcity of enteroendocrine cells and their scattered distribution make them difficult to study. Here, we glued segments of the GI wall of pigs to a silicon tube, keeping the apical and the basolateral sides separate. The fact that there was less than 1% of 70-kDa fluorescein isothiocyanate (FITC)-dextran on the basolateral side proved that the gluing was efficient. Since the lactate dehydrogenase leakage at basolateral side was lower than 0.1% (1.40 ± 0.17 nKatals) it proved that the tissue was viable. The intestinal barrier function was maintained as it is in segments mounted in Ussing chambers (the amount of Lucifer Yellow crossing it, was similar between them; respectively, % LY, 0.48 ± 0.13; 0.52 ± 0.09; p > 0.05). Finally, apical treatments with two different extract produced differential basolateral enterohormone secretions (basolateral PYY secretion vs control; animal extract, 0.35 ± 0.16; plant extract, 2.5 ± 0.74; p < 0.05). In conclusion, we report an ex vivo system called "Ap-to-Bas" for assaying vectorial transepithelial processes that makes it possible to work with several samples at the same time. It is an optimal device for enterohormone studies in the intestine.

Preclinical models for colonic absorption, application to controlled release formulation development

Oral controlled release (CR) formulations have many benefits and have become a valuable resource for the local and systemic administration of drugs. The most important characteristic of these pharmaceutical products is that drug absorption occurs mainly in the colon. Therefore, this review analyses the physiological and physicochemical features that may affect an orally administered CR product, as well as the different strategies to develop a CR dosage form and the methods used to evaluate the formulation efficacy. The models available to study the intestinal permeability and their applicability to colonic permeability determinations are also discussed.

Protein Malnutrition During Juvenile Age Increases Ileal and Colonic Permeability in Rats

Protein malnutrition can lead to morphological and functional changes in jejunum and ileum, affecting permeability to luminal contents. Regarding the large intestine, data are scarce, especially at juvenile age. We investigated whether low-protein (LP) diet could modify ileal and colonic permeability and epithelial morphology in young rats. Isocaloric diets containing 26% (control diet) or 4% protein were given to male rats between postnatal days 40 and 60. LP-diet animals failed to gain weight and displayed decreased plasma zinc levels (a marker of micronutrient deficiency). In addition, transepithelial electrical resistance and occludin expression were reduced in their ileum and colon, indicating increased gut permeability. Macromolecule transit was not modified. Finally, LP diet induced shortening of colonic crypts without affecting muscle thickness. These data show that protein malnutrition increases not only ileum but also colon permeability in juvenile rats. Enhanced exposure to colonic luminal entities may be an additional component in the pathophysiology of protein malnutrition.

Effect of toll-like receptor 3 agonist poly I:C on intestinal mucosa and epithelial barrier function in mouse models of acute colitis

AIM

To investigate potential effects of poly I:C on mucosal injury and epithelial barrier disruption in dextran sulfate sodium (DSS)-induced acute colitis.

METHODS

Thirty C57BL/6 mice were given either regular drinking water (control group) or 2% (w/v) DSS drinking water (model and poly I:C groups) ad libitum for 7 d. Poly I:C was administrated subcutaneously (20 μg/mouse) 2 h prior to DSS induction in mice of the poly I:C group. Severity of colitis was evaluated by disease activity index, body weight, colon length, histology and myeloperoxidase (MPO) activity, as well as the production of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin 17 (IL-17) and interferon-γ (IFN-γ). Intestinal permeability was analyzed by the fluorescein isothiocyanate labeled-dextran (FITC-D) method. Ultrastructural features of the colon tissue were observed under electron microscopy. Expressions of tight junction (TJ) proteins, including zo-1, occludin and claudin-1, were measured by immunohistochemistry/immunofluorescence, Western blot and real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

DSS caused significant damage to the colon tissue in the model group. Administration of poly I:C dramatically protected against DSS-induced colitis, as demonstrated by less body weight loss, lower disease activity index score, longer colon length, colonic MPO activity, and improved macroscopic and histological scores. It also ameliorated DSS-induced ultrastructural changes of the colon epithelium, as observed under scanning electron microscopy, as well as FITC-D permeability. The mRNA and protein expressions of TJ protein, zo-1, occludin and claudin-1 were also found to be significantly enhanced in the poly I:C group, as determined by immunohistochemistry/immunofluorescence, Western blot and RT-qPCR. By contrast, poly I:C pretreatment markedly reversed the DSS-induced up-regulated expressions of the inflammatory cytokines TNF-α, IL-17 and IFN-γ.

CONCLUSION

Our study suggested that poly I:C may protect against DSS-induced colitis through maintaining integrity of the epithelial barrier and regulating innate immune responses, which may shed light on the therapeutic potential of poly I:C in human colitis.

Hyaluronan mediates the adhesion of porcine peripheral blood mononuclear cells to poly (I:C)-treated intestinal cells and modulates their cytokine production

Hyaluronan (HA), a major component of the extracellular matrix (ECM), has been increasingly recognized as a regulator of inflammation. Its role is complex since it has pro- and anti-inflammatory actions by modulating the expression of inflammatory genes, the recruitment of inflammatory cells and the production of inflammatory cytokines, but also by attenuating the course of inflammation and providing protection against tissue damage. Certain viruses and other inflammatory stimuli induce organization of HA into cable-like structures, which may be responsible for leukocyte recruitment and, on the other hand, low molecular weight fragments of HA have been shown to activate various inflammatory responses. The aim of the present study was to analyze the effects of a simulated infection with the viral mimetic Poly (I:C) on HA deposition on different porcine intestinal cells (primary colonic muscular smooth muscle cells (SMC), and epithelial IPEC-J2 and IPI-2I cell lines) and on the recruitment of peripheral blood mononuclear cells (PBMC) to intestinal cell layers. We show that Poly (I:C) treatment induces the formation of an HA-based pericellular matrix coat in muscular SMC and in intestinal epithelial cells (IECs) and that, on differentiated IPEC-J2 cells, HA accumulates in the basolateral membrane. Porcine PBMCs bind to Poly (I:C)-treated cells and this binding is dependent on HA, since the increase in adhesion is abolished by hyaluronidase treatment of the cell layers. A second goal was to study the effect of different molecular weight HA forms on the production of pro-inflammatory cytokines and chemokines (TNF-α, IL-1β and IL-8) by porcine PBMCs. Low molecular weight HA fragments (100-150kDa), in contrast to high molecular weight HA (2500kDa), stimulate the release of these pro-inflammatory mediators by porcine PBMCs. Our results suggest that HA is involved in the inflammatory response against pathogenic insults to the porcine gut.

The toll-like receptor 3 pathway in homeostasis, responses to injury and wound repair

In addition to their established roles in host defence, Toll-like Receptors (TLRs) have emerging roles in control of homeostasis, injury and wound repair. The dsRNA-sensing receptor, TLR3, has been particularly implicated in such processes in several different tissues including the skin, intestine and liver, as well as in the control of reparative mechanisms in the brain, heart and kidneys, following ischemia reperfusion injury. In this review, we provide an overview of TLR3 signalling and functions in inflammation, tissue damage and repair processes, as well as therapeutic opportunities that may arise in the future from knowledge of such pathways.

Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders

The emerging links between our gut microbiome and the central nervous system (CNS) are regarded as a paradigm shift in neuroscience with possible implications for not only understanding the pathophysiology of stress-related psychiatric disorders, but also their treatment. Thus the gut microbiome and its influence on host barrier function is positioned to be a critical node within the brain-gut axis. Mounting preclinical evidence broadly suggests that the gut microbiota can modulate brain development, function and behavior by immune, endocrine and neural pathways of the brain-gut-microbiota axis. Detailed mechanistic insights explaining these specific interactions are currently underdeveloped. However, the concept that a "leaky gut" may facilitate communication between the microbiota and these key signaling pathways has gained traction. Deficits in intestinal permeability may underpin the chronic low-grade inflammation observed in disorders such as depression and the gut microbiome plays a critical role in regulating intestinal permeability. In this review we will discuss the possible role played by the gut microbiota in maintaining intestinal barrier function and the CNS consequences when it becomes disrupted. We will draw on both clinical and preclinical evidence to support this concept as well as the key features of the gut microbiota which are necessary for normal intestinal barrier function.