Molecular mechanism of intestinal permeability: interaction at tight junctions

Sodium butyrate mediates the MAPK signaling pathway and apoptosis and modulates intestinal flora to alleviate glycinin-induced intestinal injury in Cyprinus carpio

The study investigated the potential alleviating effect of sodium butyrate (SB) on intestinal injuries caused by glycinin in the diet of common carp. Fish were divided into six groups: a control group (without glycinin and SB), a Gly group (with glycinin), and four groups supplemented with different doses of SB (0.75, 1.50, 2.25, and 3.00 g/kg) based on the Gly group. All diets were isonitrogenous and isoenergetic, and the fish were fed these diets for 8 weeks. The results indicated that glycinin activated the mitogen-activated protein kinase (MAPK) signaling pathway, leading to upregulating ERK, JNK, and p38 gene expression in the intestine. However, SB2 and SB3 groups were able to inhibit this pathway. Furthermore, glycinin upregulated the expression of proapoptotic genes (Bax, Caspase-3, Caspase-8, and Caspase-9) while downregulating the antiapoptotic gene Bcl2. The SB2 and SB3 groups were found to alleviate glycinin-induced apoptosis. Additionally, dietary glycinin significantly decreased the expression of tight junction genes (ZO-1, Claudin3, Claudin7, and Occludin1) in the intestine, whereas the SB2 and SB3 groups improved intestinal barrier function. Glycinin also elevated serum levels of d-lactate, diamine oxidase, serotonin, and endothelin, resulting in intestinal damage and increased permeability. In contrast, the SB2 and SB3 groups reduced these serum levels, thereby regulating intestinal permeability. Moreover, glycinin disrupted the intestinal morphology, which was mitigated by the SB2 and SB3 groups by increasing the height and width of intestinal villi folds. Lastly, dietary glycinin altered the intestinal microecological balance by increasing Proteobacteria abundance and decreasing Clostridium and Bacteroidetes abundance. The SB2 and SB3 groups modulated the composition of dominant taxa by increasing Firmicutes and Acidobacteria abundance. Overall, SB was found to mediate the MAPK signaling pathway, apoptosis, upregulation of tight junction genes, maintenance of the intestinal physical barrier, and regulation of intestinal flora, thereby alleviating glycinin-induced intestinal damage.

Natural Epithelial Barrier Integrity Enhancers-Citrus medica and Origanum dayi Extracts

Buccal drug delivery offers a promising alternative for avoiding gastrointestinal degradation and first-pass metabolism. However, enhancing the buccal epithelial barrier's permeability remains challenging. This study explores the effects of ethanolic extracts from Citrus medica var. Balady (CM), Citrus medica var. Calabria (CMC), and Origanum dayi (ORD) on buccal epithelium permeability in vitro using a TR146 cell-based model. The cell viability assay revealed that the extracts were non-toxic at the concentration range tested (<0.5% w/v). Surprisingly, none of the tested extracts significantly enhanced the buccal permeability of 40 kDa Fluorescein Isothiocyanate Dextran (FD40). However, the CMC and ORD extracts significantly reduced the epithelial permeability of FD40, mirroring the effects of hyaluronic acid (HA), a known barrier integrity enhancer. The total phenolic content (TPC) analysis suggested a potential link between the phenolic concentration and epithelial barrier reinforcement. The rapid colorimetric response method was applied to assess the interaction of these extracts with biological membranes. The results indicated that HA interacts with cellular membranes via lipid bilayer penetration, whereas the extracts likely influence the barrier integrity through alternative mechanisms, such as ligand-receptor interactions or extracellular matrix modulation. These findings highlight the potential of CMC and ORD extracts as natural agents to enhance buccal epithelial integrity. In conclusion, incorporating these extracts into formulations, such as hydrogels, could offer a cost-effective and biocompatible alternative to HA for improving buccal cavity health.

Potential mechanisms of traditional Chinese medicine in the treatment of liver cirrhosis: a focus on gut microbiota

Cirrhosis, a pathological stage that develops from various chronic liver diseases, is characterized by liver fibrosis, pseudolobular formation, and chronic inflammation. When it progresses to the decompensated phase, the mortality rate of cirrhosis can reach 80%. The role of gut microbiota in the progression of liver diseases has received significant attention. Numerous studies have shown that regulating gut microbiota has significant therapeutic effects on preventing and reversing liver cirrhosis. This article reviewed the mechanisms by which gut microbiota influence liver cirrhosis, explaining the effective therapeutic effects of traditional Chinese medicine. Through multi-directional regulation involving signaling pathways, gut microbiota diversity, and restoration of intestinal barrier function, traditional Chinese medicine has been promising in ameliorating liver cirrhosis, providing treatment options and pharmacological guidance for the occurrence and development of liver cirrhosis.

Heat-killed Limosilactobacillus reuteri ATCC PTA 6475 prevents bone loss in ovariectomized mice: A preliminary study

Osteoporosis is an important health problem that occurs due to an imbalance between bone formation and resorption. Hormonal deficiency post-menopause is a significant risk factor. The probiotic Limosilactobacillus reuteri has been reported to prevent ovariectomy (Ovx)-induced bone loss in mice and reduce bone loss in postmenopausal women. Despite the numerous health benefits of probiotics, as they are live bacteria, the administration is not risk-free for certain groups (e.g., neonates and immunosuppressed patients). We evaluated the effects of L. reuteri (ATCC PTA 6475) and its heat-killed (postbiotic) form on Ovx-induced bone loss. Adult female mice (BALB/c) were randomly divided into four groups: group C-control (sham); group OVX-C-Ovx; group OVX-POS-Ovx + heat-killed probiotic; group OVX-PRO-Ovx + probiotic. L. reuteri or the postbiotic was administered to the groups (1.3x109 CFU/day) by gavage. Bacterial morphology after heat treatment was accessed by scanning electron microscopy (SEM). The treatment started one week after Ovx and lasted 28 days (4 weeks). The animals were euthanized at the end of the treatment period. Bone microarchitecture and ileum Occludin and pro-inflammatory cytokines gene expression were evaluated by computed microtomography and qPCR techniques, respectively. The Ovx groups had lower percentage of bone volume (BV/TV) and number of bone trabeculae as well as greater total porosity compared to the control group. Treatment with live and heat-killed L. reuteri resulted in higher BV/TV and trabecular thickness than the Ovx group. The heat treatment caused some cell surface disruptions, but its structure resembled that of the live probiotic in SEM analysis. There were no statistical differences in Occludin, Il-6 and Tnf-α gene expression. Both viable and heat-killed L. reuteri prevented bone loss on ovariectomized mice, independently of gut Occludin and intestinal Il-6 and Tnf-α gene expression.

Structural characterization and immunomodulatory effect of a starch-like Grifola frondosa polysaccharides on cyclophosphamide-induced immunosuppression in mice

In this study, a pure Grifola frondosa polysaccharide (GFP-1) was extracted and purified from Grifola frondosa. By HPLC, GC-MS, FT-IR, and NMR analysis, GFP-1 was determined to be a starch-like polysaccharide with an average molecular weight of 3370 kDa. It included three monosaccharides, i.e., glucose, galactose, and mannose. The backbone of GFP-1 consisted of →4)-α-Glcp-(1→ and →4,6)-α-Glcp-(1 → . The side branches were composed of →6)-α-Galp-(1→, α-Glcp-(1→, and a small amount of α-Manp-(1 → . By using a cyclophosphamide (CTX)-induced immunosuppressed mice model, we evaluated the immunomodulatory activity of GFP-1. The results showed that GFP-1 increased the thymic and spleen indices, promoted the level of IgG and IgA in serum, and activated the mitogen-activated protein kinase (MAPK) pathway in CTX-induced mice. Also, GFP-1 significantly promoted the mRNA expression of intestinal barrier factors and protected intestinal structural integrity in immunosuppressed mice. In conclusion, the data presented here suggested that GFP-1 might be a potential immune-enhancing supplement.

Baizhu shaoyao decoction restores the intestinal barrier and brain-gut axis balance to alleviate diarrhea-predominant irritable bowel syndrome via FoxO1/FoxO3a

BACKGROUND

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a common functional gastrointestinal disease. Besides, baizhu shaoyao decoction (BSD) is an effective treatment for IBS-D; however, its mechanism of action remains unclear.

PURPOSE

This study aims to assess the ability of BSD to therapy IBS-D and to elucidate the underlying mechanism.

METHODS

First, comprehensive analyses, including ADME (absorption, distribution, metabolism, excretion) screening, Venn analysis, Gene Ontology (GO) analysis, and network construction, were performed to characterize IBS-D-related pathways and explore the synergistic effects of BSD active compounds. Next, an IBS-D model was constructed using a three-factor superposition method of neonatal maternal separation, chronic immobilization stress stimulation, and Sennae folium aqueous extract lavage. Moreover, the impact of BSD was assessed based on the body weight, fecal water content, and abdominal withdrawal reflex (AWR), and the results of the open field test, sucrose preference test, intestinal permeability assessment, transmission electron microscopy, and TdT-mediated dUTP nick-end labeling (TUNEL) analysis. The factors that regulate the BSD effects on IBS-D were estimated using immunoblotting, quantitative reverse transcription polymerase chain reaction (q-RTPCR), immunohistochemistry, and transcriptome sequencing analyses.

RESULTS

We found that BSD improved depressive behavior, brain-gut peptide levels, and intestinal permeability induced by IBS-D by increasing the abundance of intestinal tight junctions. In addition, BSD reduced secretory immunoglobulin A levels and the number of intestinal mast cells in IBS-D rats. Network pharmacology and transcriptome sequencing analysis further revealed that the forkhead box O (FoxO) signaling pathway contributed to the BSD-induced alleviation of IBS-D, as BSD regulated the protein and mRNA levels of FoxO1, glycogen synthase kinase 3β, and FoxO3a. Importantly, a FoxO1 inhibitor effectively alleviated IBS-D symptoms in rats, whereas a FoxO3a agonist had the opposite effects.

CONCLUSION

These results demonstrate that BSD alleviates depression and intestinal symptoms by regulating brain-gut peptide expression and restoring the intestinal barrier function via the FoxO signaling pathway. Furthermore, our study uses serum pharmacochemistry technology to analyze the in vivo components of TCM formula under effective condition, solving the problem of the discovery of the effective components of TCM to some extent.

Cell-cell communications: new insights into targeting efficacy of phytochemical adjuvants on tight junctions and pathophysiology of various malignancies

Cancer is a cellular impairment disorder characterized by the loss of cell cycle regulation leading to aberrant cell proliferation. Cell-cell communication plays a crucial role in cell signaling which is highly disrupted in various malignancies. Tight junctions (TJs) are major proteins that regulate the proper communication, and the dysregulation of TJ proteins makes these tumor cells more aggressive, leading to tumor invasion and metastasis. Hence targeting TJs might be a novel insight towards addressing these highly invasive, metastatic tumors. Due to the prohibitive costs of treatments, side effects, and development of resistance, herbal medications comprising bioactive ingredients have become more popular for various human ailments. Unfortunately, the importance of natural compounds has significantly reduced due to the development of modern synthetic techniques to formulate drugs. However, the pharmaceutical industry that adopts chemistry-based drug development in combination with high throughput synthesis have not resulted in the expected drug productivity. Hence, the focus was shifted back to natural compounds in search of novel drugs with advanced technology to isolate the biologically active compound from the natural ones. The current review delivers the importance of TJ regulation, promoting it through phytochemicals to target malignant tumor cells.

Characterization and anti-inflammatory effect of selenium-enriched probiotic Bacillus amyloliquefaciens C-1, a potential postbiotics

A patented strain of Bacillus amyloliquefaciens C-1 in our laboratory could produce functional sodium selenite (Na2SeO3) under optimized fermentation conditions. With the strong stress resistance and abundant secondary metabolites, C-1 showed potential to be developed as selenium-enriched postbiotics. C-1 has the ability to synthesize SeNPs when incubated with 100 μg/ml Na2SeO3 for 30 h at 30 °C aerobically with 10% seeds-culture. The transformation rate from Na2SeO3 into SeNPs reached to 55.51%. After selenium enrichment, there were no significant morphology changes in C-1 cells but obvious SeNPs accumulated inside of cells, observed by scanning electron microscope and transmission electron microscope, verified by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. SeNPs had antioxidant activity in radical scavenge of superoxide (O2-), Hydroxyl radical (OH-) and 1,1-diphenyl-2-picryl-hydrazine (DPPH), where scavenging ability of OH- is the highest. Selenium-enriched C-1 had obvious anti-inflammatory effect in protecting integrity of Caco-2 cell membrane destroyed by S. typhimurium; it could preventing inflammatory damage in Caco-2 stressed by 200 μM H2O2 for 4 h, with significantly reduced expression of IL-8 (1.687 vs. 3.487, P = 0.01), IL-1β (1.031 vs. 5.000, P < 0.001), TNF-α (2.677 vs. 9.331, P < 0.001), increased Claudin-1 (0.971 vs. 0.611, P < 0.001) and Occludin (0.750 vs. 0.307, P < 0.001). Transcriptome data analysis showed that there were 381 differential genes in the vegetative growth stage and 1674 differential genes in the sporulation stage of C-1 with and without selenium-enrichment. A total of 22 ABC transporter protein-related genes at vegetative stage and 70 ABC transporter protein-related genes at sporulation stage were founded. Genes encoding MsrA, thiol, glutathione and thioredoxin reduction were significantly up-regulated; genes related to ATP synthase such as atpA and atpD genes showed down-regulated during vegetative stage; the flagellar-related genes (flgG, fliM, fliL, and fliJ) showed down-regulated during sporulation stage. The motility, chemotaxis and colonization ability were weakened along with synthesized SeNPs accumulated intracellular at sporulation stage. B. amyloliquefaciens C-1 could convert extracellular selenite into intracellular SeNPs through the oxidation-reduction pathway, with strong selenium-enriched metabolism. The SeNPs and selenium-enriched cells had potential to be developed as nano-selenium biomaterials and selenium-enriched postbiotics.

Pharmaceutical efficacy of novel human-origin Faecalibacterium prausnitzii strains on high-fat-diet-induced obesity and associated metabolic disorders in mice

INTRODUCTION

Obesity and related metabolic issues are a growing global health concern. Recently, the discovery of new probiotics with anti-obesity properties has gained interest.

METHODS

In this study, four Faecalibacte-rium prausnitzii strains were isolated from healthy human feces and evaluated on a high-fat diet-induced mouse model for 12 weeks.

RESULTS

The F. prausnitzii strains reduced body weight gain, liver and fat weights, and calorie intake while improving lipid and glucose metabolism in the liver and adipose tissue, as evidenced by regulating lipid metabolism-associated gene expression, including ACC1, FAS, SREBP1c, leptin, and adiponectin. Moreover, the F. prausnitzii strains inhibited low-grade inflammation, restored gut integrity, and ameliorated hepatic function and insulin resistance. Interestingly, the F. prausnitzii strains modulated gut and neural hormone secretion and reduced appetite by affecting the gut-brain axis. Supplementation with F. prausnitzii strains noticeably changed the gut microbiota composition.

DISCUSSION

In summary, the novel isolated F. prausnitzii strains have therapeutic effects on obesity and associated metabolic disorders through modulation of the gut-brain axis. Additionally, the effectiveness of different strains might not be achieved through identical mechanisms. Therefore, the present findings provide a reliable clue for developing novel therapeutic probiotics against obesity and associated metabolic disorders.

Genome-wide identification, evolution and expression analysis of tight junction gene family and the immune roles of claudin5 gene in turbot (Scophthalmus maximus L.)

Tight junction proteins (TJs) are important component proteins that maintaining the structure and function of TJs, connecting to each other to form a TJ complex between cells, maintaining the biological homeostasis of the internal environment. In this study, a total of 103 TJ genes were identified in turbot according to our whole-transcriptome database. Transmembrane TJs were divided into seven subfamilies, including claudin (CLDN), occludin (OCLD), tricellulin (MARVELD2), MARVEL domain containing 3 (MARVELD3), junctional adhesion molecules (JAM), immunoglobulin superfamily member 5 (IGSF5/JAM4), blood vessel epicardial substance (BVEs). Moreover, the majority of homologous pairs of TJ genes showed highly conserved alongside length, exon/intron number and motifs. As for phylogenetic analysis for 103 TJ genes, eight of them have undergone a positive selection and JAMB-like has undergone the most neutral evolution. The expression patterns of several TJ genes showed the lowest expression levels in blood, while the highest expression levels were detected in intestine, gill and skin, which all belong to mucosal tissues. Meanwhile, most examined TJ genes showed down-regulated expression patterns during bacterial infection, while several TJ genes exhibited up-regulated expression patterns at a later stage (24 h). At the same time, several potential candidate genes (such as CLDN-15, CLDN-3, CLDN-12, CLDN-5 and OCLD) were significantly down-regulated, which may indicate their important functions that involved in the regulation of bacterial infection. Currently, there is little research on CLDN5 in the intestine, but it is highly expressed in the intestine and has significant changes in intestinal expression after bacterial infection. Thus, we knocked down CLDN5 by the method of lentiviral infection. The result showed CLDN5 was related to cell migration (wound healing) and apoptosis, and the method of dualluciferasereporterassay showed that the functions of CLDN5 could be regulated by miR-24. The study of TJs may lead to a better understanding of the function of TJs in teleost.

Direct and indirect effects of pathogenic bacteria on the integrity of intestinal barrier

Bacterial translocation is a pathological process involving migration of pathogenic bacteria across the intestinal barrier to enter the systemic circulation and gain access to distant organs. This phenomenon has been linked to a diverse range of diseases including inflammatory bowel disease, pancreatitis, and cancer. The intestinal barrier is an innate structure that maintains intestinal homeostasis. Pathogenic infections and dysbiosis can disrupt the integrity of the intestinal barrier, increasing its permeability, and thereby facilitating pathogen translocation. As translocation represents an essential step in pathogenesis, a clear understanding of how barrier integrity is disrupted and how this disruption facilitates bacterial translocation could identify new routes to effective prophylaxis and therapy. In this comprehensive review, we provide an in-depth analysis of bacterial translocation and intestinal barrier function. We discuss currently understood mechanisms of bacterial-enterocyte interactions, with a focus on tight junctions and endocytosis. We also discuss the emerging concept of bidirectional communication between the intestinal microbiota and other body systems. The intestinal tract has established 'axes' with various organs. Among our regulatory systems, the nervous, immune, and endocrine systems have been shown to play pivotal roles in barrier regulation. A mechanistic understanding of intestinal barrier regulation is crucial for the development of personalized management strategies for patients with bacterial translocation-related disorders. Advancing our knowledge of barrier regulation will pave the way for future research in this field and novel clinical intervention strategies.

Gastrointestinal structure and function of preweaning dairy calves fed a whole milk powder or a milk replacer high in fat

The composition of milk replacer (MR) for calves greatly differs from that of bovine whole milk, which may affect gastrointestinal development of young calves. In this light, the objective of the current study was to compare gastrointestinal tract structure and function in response to feeding liquid diets having a same macronutrient profile (e.g., fat, lactose, protein) in calves in the first month of life. Eighteen male Holstein calves (46.6 ± 5.12 kg; 1.4 ± 0.50 d of age at arrival; mean ± standard deviation) were housed individually. Upon arrival, calves were blocked based on age and arrival day, and, within a block, calves were randomly assigned to either a whole milk powder (WP; 26% fat, DM basis, n = 9) or a MR high in fat (25% fat, n = 9) fed 3.0 L 3 times daily (9 L total per day) at 135 g/L through teat buckets. On d 21, gut permeability was assessed with indigestible permeability markers [chromium (Cr)-EDTA, lactulose, and d-mannitol]. On d 32 after arrival, calves were slaughtered. The weight of the total forestomach without contents was greater in WP-fed calves. Furthermore, duodenum and ileum weights were similar between treatment groups, but jejunum and total small intestine weights were greater in WP-fed calves. The surface area of the duodenum and ileum did not differ between treatment groups, but the surface area of the proximal jejunum was greater in calves fed WP. Urinary lactulose and Cr-EDTA recoveries were greater in calves fed WP in the first 6 h post marker administration. Tight junction protein gene expression in the proximal jejunum or ileum did not differ between treatments. The free fatty acid and phospholipid fatty acid profiles in the proximal jejunum and ileum differed between treatments and generally reflected the fatty acid profile of each liquid diet. Feeding WP or MR altered gut permeability and fatty acid composition of the gastrointestinal tract and further investigation are needed to understand the biological relevance of the observed differences.

The interplay between herbal medicines and gut microbiota in metabolic diseases

Globally, metabolic diseases are becoming a major public health problem. Herbal medicines are medicinal materials or preparations derived from plants and are widely used in the treatment of metabolic diseases due to their good curative effects and minimal side effects. Recent studies have shown that gut microbiota plays an important role in the herbal treatment of metabolic diseases. However, the mechanisms involved are still not fully understood. This review provides a timely and comprehensive summary of the interactions between herbal medicines and gut microbiota in metabolic diseases. Mechanisms by which herbal medicines treat metabolic diseases include their effects on the gut microbial composition, the intestinal barrier, inflammation, and microbial metabolites (e.g., short-chain fatty acids and bile acids). Herbal medicines can increase the abundance of beneficial bacteria (e.g., Akkermansia and Blautia), reduce the abundance of harmful bacteria (e.g., Escherichia-Shigella), protect the intestinal barrier, and alleviate inflammation. In turn, gut microbes can metabolize herbal compounds and thereby increase their bioavailability and bioactivity, in addition to reducing their toxicity. These findings suggest that the therapeutic effects of herbal medicines on metabolic diseases are closely related to their interactions with the gut microbiota. In addition, some methods, and techniques for studying the bidirectional interaction between herbal medicines and gut microbiota are proposed and discussed. The information presented in this review will help with a better understanding of the therapeutic mechanisms of herbal medicines and the key role of gut microbiota.

Effects of Dietary Nutrients on Fatty Liver Disease Associated With Metabolic Dysfunction (MAFLD): Based on the Intestinal-Hepatic Axis

Non-alcoholic fatty liver disease (NAFLD) has recently become the most common liver disease with a global prevalence of over 25% and is expected to increase. Recently, experts have reached a consensus that “fatty liver disease associated with metabolic dysfunction or MAFLD” may be a more appropriate and inclusive definition than NAFLD. Like the former name NAFLD, MAFLD, as a manifestation of multiple system metabolic disorders involving the liver, has certain heterogeneity in its pathogenesis, clinical manifestations, pathological changes and natural outcomes. We found that there is a delicate dynamic balance among intestinal microflora, metabolites and host immune system to maintain a healthy intestinal environment and host health. On the contrary, this imbalance is related to diseases such as MAFLD. However, there are no clear studies on how dietary nutrients affect the intestinal environment and participate in the pathogenesis of MAFLD. This review summarizes the interactions among dietary nutrients, intestinal microbiota and MAFLD in an attempt to provide evidence for the use of dietary supplements to regulate liver function in patients with MAFLD. These dietary nutrients influence the development and progression of MAFLD mainly through the hepatic-intestinal axis by altering dietary energy absorption, regulating bile acid metabolism, changing intestinal permeability and producing ethanol. Meanwhile, the nutrients have the ability to combat MAFLD in terms of enriching abundance of intestinal microbiota, reducing Firmicutes/Bacteroidetes ratio and promoting abundance of beneficial gut microbes. Therefore, family therapy with MAFLD using a reasonable diet could be considered.

Microbial short-chain fatty acids: a bridge between dietary fibers and poultry gut health

The maintenance of poultry gut health is complex depending on the intricate balance among diet, the commensal microbiota, and the mucosa, including the gut epithelium and the superimposing mucus layer. Changes in microflora composition and abundance can confer beneficial or detrimental effects on fowl. Antibiotics have devastating impacts on altering the landscape of gut microbiota, which further leads to antibiotic resistance or spread the pathogenic populations. By eliciting the landscape of gut microbiota, strategies should be made to break down the regulatory signals of pathogenic bacteria. The optional strategy of conferring dietary fibers (DFs) can be used to counterbalance the gut microbiota. DFs are the non-starch carbohydrates indigestible by host endogenous enzymes but can be fermented by symbiotic microbiota to produce short-chain fatty acids (SCFAs). This is one of the primary modes through which the gut microbiota interacts and communicate with the host. The majority of SCFAs are produced in the large intestine (particularly in the caecum), where they are taken up by the enterocytes or transported through portal vein circulation into the bloodstream. Recent shreds of evidence have elucidated that SCFAs affect the gut and modulate the tissues and organs either by activating G-protein-coupled receptors or affecting epigenetic modifications in the genome through inducing histone acetylase activities and inhibiting histone deacetylases. Thus, in this way, SCFAs vastly influence poultry health by promoting energy regulation, mucosal integrity, immune homeostasis, and immune maturation. In this review article, we will focus on DFs, which directly interact with gut microbes and lead to the production of SCFAs. Further, we will discuss the current molecular mechanisms of how SCFAs are generated, transported, and modulated the pro-and anti-inflammatory immune responses against pathogens and host physiology and gut health.

Relationship between Eimeria tenella associated-early clinical signs and molecular changes in the intestinal barrier function

The major clinical signs of coccidiosis in chickens due to Eimeria parasite are diarrhea and bloody feces. Previous studies showed that the impairment of the intestinal epithelial barrier and the elevation of the intestinal permeability are causes of clinical signs associated with coccidia challenges. Nevertheless, the information about molecular changes of the epithelial barrier at the early stage of the infection with a specific Eimeria species has not been mentioned. Hence, this study aims to elucidate the temporal relationships between epithelial barrier conditions and clinical signs in chickens infected with Eimeria tenella over the time from the earliest stages of infection. White Leghorn chickens were inoculated with 1 × 10⁴ oocysts of E. tenella. Thereafter the chickens were monitored for their daily clinical signs through observation, and between 5 dpi to 10 dpi, feces were collected for oocysts counting. Chickens were then administrated with fluorescein isothiocyanate-dextran (FITC-d) for gastrointestinal permeability test and tissues were collected each day for histopathological observation and total RNA extraction. Finally, the mRNA expression levels of the tight and adherens junction genes and cytokine genes were evaluated using the quantitative real-time polymerase chain reaction (qRT-PCR). In this study, clinical signs such as diarrhea and bloody feces were observed concurrently from 3 to 8 dpi. Histopathology changes such as severe inflammation, hemorrhage, and epithelial desquamation were identified in the cecum specimens. The FITC-d level in the E. tenella-infected group was significantly higher than in the control group. In the infected group, the expression of claudin-2 gene was also upregulated, whereas the expressions of claudin-3 and E-cadherin genes were decreased as compared to the control group. These results implied that clinical signs of avian coccidiosis were associated with the intestinal barrier disruption via changes in expression levels of claudins and E-cadherin at the intestine.

Probiotics Stimulate Bone Formation in Obese Mice via Histone Methylations

Rationale: Manipulation of the gut microbiome can prevent pathologic bone loss. However, the effects of probiotics on mitochondrial epigenetic remodeling and skeletal homeostasis in the high-fat diet (HFD)-linked obesity remains to be explored. Here, we examined the impact of probiotics supplementation on mitochondrial biogenesis and bone homeostasis through the histone methylation mechanism in HFD fed obese mice.

Methods: 16S rRNA gene sequencing was performed to study the microbiota composition in the gut and microbial dysbiosis in obese mouse model. High resolution (microPET/CT) imaging was performed to demonstrate the obese associated colonic inflammation. Obese-associated upregulation of target miRNA in osteoblast was investigated using a microRNA qPCR array. Osteoblastic mitochondrial mass was evaluated using confocal imaging. Overexpression of mitochondrial transcription factor (Tfam) was used to investigate the glycolysis and mitochondrial bioenergetic metabolism using Tfam-transgenic (Tg) mice fed on HFD. The bone formation and mechanical strength was evaluated by microCT analysis and three-point bending analysis.

Results: High-resolution imaging (µ-CT) and mechanical testing revealed that probiotics induced a significant increase of trabecular bone volume and bone mechanical strength respectively in obese mice. Probiotics or Indole-3-propionic acid (IPA) treatment directly to obese mice, prevents gut inflammation, and improved osteoblast mineralization. Mechanistically, probiotics treatment increases mitochondrial transcription factor A (Tfam) expression in osteoblasts by promoting Kdm6b/Jmjd3 histone demethylase, which inhibits H3K27me3 epigenetic methylation at the Tfam promoter. Furthermore, Tfam-transgenic (Tg) mice, fed with HFD, did not experience obesity-linked reduction of glucose uptake, mitochondrial biogenesis and mineralization in osteoblasts.

Conclusions: These results suggest that the probiotics mediated changes in the gut microbiome and its derived metabolite, IPA are potentially be a novel agent for regulating bone anabolism via the gut-bone axis.

Occludin endocytosis is involved in the disruption of the intestinal epithelial barrier in a mouse model of alcoholic steatohepatitis

OBJECTIVE

We aimed to investigate the involvement of the endocytosis of occludin, a key component of tight junction (TJ), in the ethanol-induced disassembly of TJ in a model of alcoholic steatohepatitis.

METHODS

Wild-type mice were fed an ethanol-containing or isocaloric liquid diet for 8 weeks and then assessed for liver injury (histopathology and measurement of serum enzymes), gut permeability (in vivo lactulose/mannitol and ex vivo dye leakage assays), intestinal epithelium ultrastructure (transmission electron microscopy), and intestinal occludin localization (immunofluorescence microscopy). The human intestinal epithelial cell line Caco-2 was also analyzed in vitro for the effects of ethanol on the barrier function (transepithelial electrical resistance), occludin localization (immunofluorescence microscopy and Western blotting), and endocytosis pathways (double-labeling immunofluorescence microscopy with selective pathway inhibitors).

RESULTS

The ethanol-fed mice developed steatohepatitis and displayed intestinal barrier dysfunction, the disruption of intestinal TJ, and enhanced intestinal endocytosis of occluding compared with the control mice. In the Caco-2 monolayers, ethanol treatment decreased transepithelial electrical resistance, disrupted TJ formation, and enhanced occludin endocytosis in a dose- and time-dependent manner. These deleterious events were reversed by pretreating the Caco-2 cells with a selective pharmacological inhibitor of macropinocytosis, but not with the inhibitors of clathrin or caveolin-mediated endocytic pathways.

CONCLUSION

Chronic ethanol exposure may increase intestinal permeability by inducing the micropinocytosis of occludin, resulting in the disruption of intestinal TJ.

Berberine improves intestinal epithelial tight junctions by upregulating A20 expression in IBS-D mice

To investigate effects of berberine exerts on A20 expression and regulation of intestinal epithelial tight junctions via the TNF-α-NF-κB-MLCK pathway in Diarrhea-Predominant Irritable Bowel Syndrome (IBS-D). C57BL/6 wild type (WT) and A20 IEC-KO mice (48 each) were randomly divided into normal control (NC), model control (MC), rifaximin and berberine groups (12 mice per group). An experimental model of IBS-D was established using 4% acetic acid and evaluated by haematoxylin-eosin (HE) staining. rifaximin and berberine mice were treated with rifaximin and berberine, respectively. Intestinal epithelial space of WT berberine mice improved more than A20 IEC-KO berberine mice compared to MC mice. WT berberine mice exhibited greater expression of A20 compared with MC mice(P < 0.01). TNF-α, NF-kB p65, MLCK, MLC, TRAF6 and RIP1 levels in A20 IEC-KO and WT berberine mice were all decreased compared to MC mice(P all<0.05). NF-κB p65, MLCK and TRAF6 levels were increased in A20 IEC-KO berberine mice as compared to WT berberine mice (P all<0.05). Intestinal epithelial levels of occludin, claudin-1, ZO-1 and F-actin increased in all berberine mice (P all<0.01-0.05), while occludin, claudin-1, and ZO-1 levels were lower in A20 IEC-KO berberine mice(P < 0.05). Berberine downregulates abnormal activation of the TNF-α-NF-κB-MLCK pathway by upregulating expression of A20 in a mouse model of IBS-D, thereby protecting intestinal epithelial tight junctions and repairing the damage IBS-D causes to the intestinal epithelial barrier.

High fat diet exacerbates intestinal barrier dysfunction and changes gut microbiota in intestinal-specific ACF7 knockout mice

Microtubule-actin cross-linking factor-1 (ACF7, or MACF1) regulates cytoskeletal focal adhesion dynamics and migration in various tissues. High fat diet (HFD) induces gut microbiota dysbiosis and metabolic disorders, and increases intestinal permeability and inflammatory response. Here we investigated the synergistic effects of intestinal ACF7 conditional knockout (ACF7 cKO) and HFD on metabolism phenotypes, gut microbiota and intestinal barrier function in mice. ACF7 cKO and control (ACF7fl/fl) mice (8-week-old) were fed with either chow diet or HFD, for 16 weeks. The increase of body weight and fat pad weight were impaired in HFD-fed ACF7 cKO mice, which can be attributed to decreased food intake and absorption. The metabolic status of HFD-fed ACF7 cKO mice was dramatically changed when compared to the other groups. In addition, HFD-fed ACF7 cKO mice had increased epithelial cell apoptosis, intestinal permeability and inflammatory response when compared with the other groups. The ACF7 cKO-induced changes in alimentation, intestinal barrier function, and gut microbiota were independent of dietary treatment. Taken together, our studies for the first time proved HFD and ACF7 cKO have synergistic damaging effects on intestinal homeostasis. ACF7 is a crucial protective molecule in HFD-induced intestinal diseases.

Antimicrobial peptide LL-37 forms complex with bacterial DNA to facilitate blood translocation of bacterial DNA and aggravate ulcerative colitis

Bacterial DNA (bacDNA) is frequently found in serum of patient with ulcerative colitis (UC) and Crohn's disease, even blood bacterial culture is negative. How bacDNA evades immune elimination and is translocated into blood remain unclear. Here, we showed that bacDNA avoids elimination and disables bacteria-killing function of antimicrobial peptide LL-37 (Cramp in mice) by forming complex with LL-37, which is inducible after culture with bacteria or bacterial products. Elevated LL-37-bacDNA complex was found in plasma and lesions of patients with UC. LL-37-bacDNA promoted inflammation by inducing Th1, Th2 and Th17 differentiation and activating toll-like receptor-9 (TLR9). The complex also increased paracellular permeability, which possibly combines its inflammatory effects to promote local damage and bacDNA translocation into blood. Cramp-bacDNA aggravated mouse colitis severity while interference with the complex ameliorated the disease. The study identifies that inflammatogenic bacDNA utilizes LL-37 as a vehicle for blood translocation and to evade immune elimination. Additionally, bacteria may make a milieu by releasing bacDNA to utilize and resist host antimicrobial peptides as a 'trojan horse'.

[Claudin-3 expression in colorectal carcinoma and its significance]

OBJECTIVE

To investigate the expression of claudin-3 in colorectal carcinoma and its association with the occurrence, progression and prognosis of colorectal cancer.

METHODS

Forty surgical specimens of colorectal carcinoma and 22 adjacent normal tissues resected between October, 2010 and January, 2013 at Nanfang Hospital were examined for claudin-3 expression using immunohistochemistry, which was analyzed in association with the clinicopathological parameters and the survival of the patients.

RESULTS

Claudin-3 was expressed mainly on the cell membrane, and its positivity rate was significantly higher in cancer tissues than in normal tissues (92.50% vs 59.09%, P<0.05). In 13 cases claudin-3 expression was detected in both the cancer tissues and adjacent normal tissues with average expression scores of 4.538 and 3.269, respectively (P<0.05). In the cancer tissues, the strongly positive expression rate was significantly higher in poorly differentiated tissues (85.71%) than in well (21.43%) and moderately (36.48%) differentiated tissues (P<0.05), and was higher in cases with lymph node metastasis than in those without (61.11% vs 22.72%, P<0.05). The strongly positive expression rate of claudin-3 was not correlated with the patients'age, gender, tumor location or tumor size (P>0.05). Of the 33 cancer patients followed up, 14 had a postoperative survival time no longer than 3 years and 19 had longer survival time, and their average expression scores differed significantly (4.50 vs 3.526, P<0.05).

CONCLUSION

Claudin-3 is over-expressed in colorectal cancer tissues, and its high expression may promote the occurrence and progression of colorectal cancer. Claudin-3 may serve as a molecular biomarker for early diagnosis and prognostic evaluation.

Resveratrol Protects Oxidative Stress-Induced Intestinal Epithelial Barrier Dysfunction by Upregulating Heme Oxygenase-1 Expression

BACKGROUND/AIM

Obstructive jaundice (OJ) is frequently complicated by infections and has been associated with increased bacterial translocation, intestinal epithelial hyperpermeability, and oxidative stress, but the mechanism remains unclear. The potential effect of resveratrol (Res) on modifying intestinal epithelial dysfunction was evaluated both in vitro and in vivo.

METHODS

Caco-2 cells (in vitro) and male Wistar rats (n = 60; in vivo) were used to evaluate the role of Res on intestinal epithelial dysfunction. Hydrogen peroxide was used to induce oxidative stress in the Caco-2 cells. In bile duct-ligated group, OJ was successfully established on Day 7 after bile duct ligation, whereas sham-operated and vehicle-treated rats served as controls. Western blot and RT-qPCR were performed to analyze TJ proteins expression in epithelium isolated from rat intestine.

RESULTS

Intestinal hyperpermeability was associated with decreased expression and phosphorylation of occludin and zonula occluden (ZO-1), but increased oxidation in Caco-2 cells and the intestinal epithelium. Res treatment increased the epithelial expression and phosphorylation of occludin and ZO-1 in a concentration-dependent manner. Moreover, Res which protected Caco-2 cells from H2O2-induced oxidative damage clearly reduced malondialdehyde level and intracellular reactive oxygen species accumulation, but increased the expression levels of superoxide dismutase and heme oxygenase-1 (HO-1). Further studies showed that Res also inhibited H2O2-induced protein kinase C activity and p38 phosphorylation. Interestingly, these effects of Res were abolished by the HO-1 inhibitor zinc protoporphyrin or knockdown of HO-1 by siRNA.

CONCLUSIONS

Res protected gut barrier function possibly by initiating HO-1-dependent signaling which is essential for common expression of key tight junction proteins. It also provides a rationale to develop Res clinical applications of intestinal disorders.

Protective effect of simvastatin on impaired intestine tight junction protein ZO-1 in a mouse model of Parkinson's disease

Recently, several studies showed that gastrointestinal tract may be associated with pathophysiology of Parkinson's disease (PD). Intestine tight junction protein zonula occluden-1 (ZO-1) is an important component of intestinal barrier which can be degraded by matrix metallopeptidase 9 (MMP-9). In our previous study, a significant decline in ZO-1 was observed along with enhanced MMP-9 activity in the duodenum and distal colon of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In this study, the protective effect of simvastatin on ZO-1 was investigated using an MPTP mouse model of PD. Seven days after the end of MPTP application, the expression level of ZO-1 was evaluated by immunohistochemistry. The protein expression levels of ZO-1 and MMP9 were detected by Western blotting. Meanwhile, MMP-9 activity was analyzed by gelatin zymography. MPTP treatment led to a decrease in the expression of ZO-1, which was accompanied by elevated MMP-9 activity. Treatment with simvastatin could partly reverse the MPTP-induced changes in ZO-1 expression and reduce MMP-9 protein and activity. Taken together, these findings suggest that simvastatin administration may partially reverse the impairment of ZO-1 induced by MPTP via inhibiting the activity of MMP9, fortify the impaired intestinal barrier and limit gut-derived toxins that pass across the intestinal barrier.

Oral Administration of Escin Inhibits Acute Inflammation and Reduces Intestinal Mucosal Injury in Animal Models

The present study aimed to investigate the effects of oral administration of escin on acute inflammation and intestinal mucosal injury in animal models. The effects of escin on carrageenan-induced paw edema in a rat model of acute inflammation, cecal ligation and puncture (CLP) induced intestinal mucosal injury in a mouse model, were observed. It was shown that oral administration of escin inhibits carrageenan-induced paw edema and decreases the production of prostaglandin E2 (PGE2) and cyclooxygenase- (COX-) 2. In CLP model, low dose of escin ameliorates endotoxin induced liver injury and intestinal mucosal injury and increases the expression of tight junction protein claudin-5 in mice. These findings suggest that escin effectively inhibits acute inflammation and reduces intestinal mucosal injury in animal models.

Mechanisms underlying protective effects of probiotics on intestinal epithelial

Intestinal epithelial cells (IECs), the first line of defense against pathogens, are an initial point of contact between the host and intestinal microbes. Growing evidence suggests that the interactions between the host and intestinal microbes may lead to dysregulated immune responses, while probiotics can reinforce the barrier function and exert a modest stimulation of the immune system to prevent this situation. On one hand, probiotics exert antagonistic functions via competition for nutrients, metabolites, and occupying effect. Therefore, probiotics can regulate the endogenous gastrointestinal flora and restrain exogenous pathogenic bacteria. On the other hand, IECs recognize probiotics and their metabolites through pattern recognition receptors to stimulate the non-specific immune responses. In addition, probiotics can induce IECs to produce the mucus layer covering the entire intestinal tract and prevent attachment and invasion of various bacterial pathogens. Clinical trials have also shown beneficial effects of probiotics as a potential preventive method for inflammatory bowel disease such as Crohn disease and ulcerative colitis.

Intestinal mucosal tolerance and impact of gut microbiota to mucosal tolerance

The mucosal barriers are very sensitive to pathogenic infection, thereby assuming the capacity of the mucosal immune system to induce protective immunity to harmful antigens and tolerance against harmless substances. This review provides current information about mechanisms of induction of mucosal tolerance and about impact of gut microbiota to mucosal tolerance.

A gut microbial metabolite of linoleic acid, 10-hydroxy-cis-12-octadecenoic acid, ameliorates intestinal epithelial barrier impairment partially via GPR40-MEK-ERK pathway

Gut microbial metabolites of polyunsaturated fatty acids have attracted much attention because of their various physiological properties. Dysfunction of tight junction (TJ) in the intestine contributes to the pathogenesis of many disorders such as inflammatory bowel disease. We evaluated the effects of five novel gut microbial metabolites on tumor necrosis factor (TNF)-α-induced barrier impairment in Caco-2 cells and dextran sulfate sodium-induced colitis in mice. 10-Hydroxy-cis-12-octadecenoic acid (HYA), a gut microbial metabolite of linoleic acid, suppressed TNF-α and dextran sulfate sodium-induced changes in the expression of TJ-related molecules, occludin, zonula occludens-1, and myosin light chain kinase. HYA also suppressed the expression of TNF receptor 2 (TNFR2) mRNA and protein expression in Caco-2 cells and colonic tissue. In addition, HYA suppressed the protein expression of TNFR2 in murine intestinal epithelial cells. Furthermore, HYA significantly up-regulated G protein-coupled receptor (GPR) 40 expression in Caco-2 cells. It also induced [Ca(2+)]i responses in HEK293 cells expressing human GPR40 with higher sensitivity than linoleic acid, its metabolic precursor. The barrier-recovering effects of HYA were abrogated by a GPR40 antagonist and MEK inhibitor in Caco-2 cells. Conversely, 10-hydroxyoctadacanoic acid, which is a gut microbial metabolite of oleic acid and lacks a carbon-carbon double bond at Δ12 position, did not show these TJ-restoring activities and down-regulated GPR40 expression. Therefore, HYA modulates TNFR2 expression, at least partially, via the GPR40-MEK-ERK pathway and may be useful in the treatment of TJ-related disorders such as inflammatory bowel disease.

HIV protease inhibitors in gut barrier dysfunction and liver injury

The development of HIV protease inhibitors (HIV PIs) has been one of the most significant advances of the past two decades in controlling HIV infection. HIV PIs have been used successfully in highly active anti-retroviral therapy (HAART) for HIV infection, which is currently the most effective treatment available. Incorporation of HIV PIs in HAART causes profound and sustained suppression of viral replication, significantly reduces the morbidity and mortality of HIV infection, and prolongs the lifespan of HIV patients. However, in the era of HAART, drug-induced gastrointestinal (GI) side effects and hepatotoxicity have emerged as important potential complications of HIV therapy, particularly those regimens containing HIV PIs. In this mini-review, we highlight the current understanding of the mechanisms of HIV PI-associated GI and liver injury.

ERK1/2 participates in regulating the expression and distribution of tight junction proteins in the process of reflux esophagitis

OBJECTIVE

To investigate the alterations of esophageal epithelial barrier during the process of reflux esophagitis (RE).

METHODS

In total, 85 Sprague-Dawley rats were randomly divided into two groups, the sham-operation group (n = 25) and the RE group induced by incomplete pyloric ligation (n = 60). The establishment of RE model and the severity of esophagitis were evaluated by hematoxylin and eosin stain. Dilated intercellular spaces (DIS) in the esophageal epithelium were observed by transmission electron microscopy. The cellular distributions of ZO-1, occludin and claudin-1 were assessed by immunohistochemical stain. The expressions of these tight junction (TJ) proteins and the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), myosin light chain (MLC) and nonmuscular myosin light chain kinase (nmMLCK) were analyzed by Western blot.

RESULTS

DIS occurred gradually in the RE group. ZO-1, occludin and claudin-1 were incompletely or even not expressed in the RE group. TJ proteins were expressed in the membrane instead of the cytoplasm in many epithelial cells in RE. With Western, the expression of ZO-1, occludin and claudin-1 was increased gradually in the RE group (P < 0.05). The phosphorylation levels of nmMLCK, MLC and ERK1/2 were also increased (P < 0.05). There was no marked changes in the esophageal epithelium in the sham-operation group.

CONCLUSIONS

TJ proteins could be used as sensitive markers of RE instead of DIS. ERK1/2 may participate in regulating TJ proteins in esophageal epithelia in RE.

Claudins and other tight junction proteins

Epithelial transport relies on the proper function and regulation of the tight junction (TJ), other-wise uncontrolled paracellular leakage of solutes and water would occur. They also act as a fence against mixing of membrane proteins of the apical and basolateral side. The proteins determining paracellular transport consist of four transmembrane regions, intracellular N and C terminals, one intracellular and two extracellular loops (ECLs). The ECLs interact laterally and with counterparts of the neighboring cell and by this achieve a general sealing function. Two TJ protein families can be distinguished, claudins, comprising 27 members in mammals, and TJ-associated MARVEL proteins (TAMP), comprising occludin, tricellulin, and MarvelD3. They are linked to a multitude of TJ-associated regulatory and scaffolding proteins. The major TJ proteins are classified according to the physiological role they play in enabling or preventing paracellular transport. Many TJ proteins have sealing functions (claudins 1, 3, 5, 11, 14, 19, and tricellulin). In contrast, a significant number of claudins form channels across TJs which feature selectivity for cations (claudins 2, 10b, and 15), anions (claudin-10a and -17), or are permeable to water (claudin-2). For several TJ proteins, function is yet unclear as their effects on epithelial barriers are inconsistent (claudins 4, 7, 8, 16, and occludin). TJs undergo physiological and pathophysiological regulation by altering protein composition or abundance. Major pathophysiological conditions which involve changes in TJ protein composition are (1) effects of pathogens binding to TJ proteins, (2) altered TJ protein composition during inflammation and infection, and (3) altered TJ protein expression in cancers.

CELL BIOLOGY SYMPOSIUM: Impacts of maternal obesity on placental and gut inflammation and health

Obesity in pregnant women is a growing public health concern that negatively affects fetal development and has long-term impacts on offspring health. The placenta plays an essential role in nutrient transport to the fetus and supports fetal growth and development. Maternal obesity (MO) induces an exacerbated proinflammatory milieu in the placenta providing an inflammatory environment for fetuses. The gut is one of the largest immune organs and mainly develops during the fetal stage. Maternal obesity and the corresponding inflammatory uteroplacental environment affect gut development, incurring inflammatory responses in the fetal intestine that further prime or program the offspring gut to enhance inflammation and impair intestinal barrier integrity. This review summarizes the impact of MO on inflammatory responses in placenta and fetal intestine and the long-term effects on offspring intestinal health. Because "leaky gut" is one of the main etiological factors for a number of common diseases, including inflammatory bowel diseases, type I diabetes, and related autoimmune diseases, the adverse effect of MO on the overall health of progeny is further discussed.

Genes regulating tight junctions and cell adhesion are altered in early experimental necrotizing enterocolitis

BACKGROUND/PURPOSE

Necrotizing enterocolitis (NEC) represents one of the gravest complications in preterm infants and carries significant morbidity and mortality. Increased intestinal permeability may play an important role in the pathogenesis of NEC. In this study we investigated the genes regulating structural proteins such as tight junctions (TJ) and cell adhesion in a neonatal rat model of early NEC.

METHODS

The studies were performed on Sprague-Dawley rat pups. Experimental NEC was induced using hypoxia/re-oxygenation treatment on day 1 after birth. Intestinal specimens from the ileum were obtained, mRNA was purified, and the transcriptome was analyzed using microarray.

RESULTS

We found several TJ genes such as claudins 1, 8, 14, 15, and gap junction protein to be affected. Alterations in genes involved in the inflammatory response was confirmed, along with several genes regulating proteins used as biomarkers for NEC.

CONCLUSION

This study indicates that tight junctions and cell adhesion may play a critical role in the pathogenesis of early experimental NEC. Better understanding of the pathogenesis of NEC may lead to novel strategies for the prevention and treatment of NEC.

Pathogenesis of intestinal barrier dysfunction in obstructive jaundice

Intestinal mucosal barrier is a key structure that normally prevents the passage of harmful molecules across the mucosa and into the circulation, including mechanical barrier, immunological barrier, biological barrier and chemical barrier. Obstructive jaundice (OJ) is frequently associated with infectious complications, mainly due to sepsis and renal dysfunction. The key events in the pathophysiology of these complications are endotoxemia of gut origin and increased intestinal permeability because of intestinal barrier dysfunction, as demonstrated in experimental and clinical studies. However, the mechanisms involved in this phenomenon remain obscure. Here we review recent progress in understanding the pathogenesis of intestinal barrier dysfunction in OJ.

Entamoeba histolytica contains an occludin-like protein that can alter colonic epithelial barrier function

The exact mechanism by which Entamoeba histolytica disrupts the human colonic epithelium and invades the mucosa has yet to be clearly elucidated. E. histolytica produces a diverse array of putative virulent factors such as glycosidase, cysteine proteinases and amebapore that can modulate and/or disrupt epithelial barrier functions. However, it is currently thought that E. histolytica produces numerous other molecules and strategies to disrupt colonic mucosal defenses. In this study, we document a putative mechanism whereby the parasite alters the integrity of human epithelium by expressing a cognate tight junction protein of the host. We detected this protein as “occludin-like” as revealed by immunoblotting and immunoprecipitation studies and visualization by confocal microscopy using antibodies highly specific for human occludin. We propose that E. histolytica occludin-like protein might displace mucosal epithelial occludin-occludin tight junction interactions resulting in epithelial disruption analogous to sub mucosal human dendritic cells sampling luminal contents. These results indicate that E. histolytica occludin is a putative virulent component that can play a role in the pathogenesis of intestinal amebiasis.

Claudins in intestines: Distribution and functional significance in health and diseases

Intestines are organs that not only digest food and absorb nutrients, but also provide a defense barrier against pathogens and noxious agents ingested. Tight junctions (TJs) are the most apical component of the junctional complex, providing one form of cell-cell adhesion in enterocytes and playing a critical role in regulating paracellular barrier permeability. Alteration of TJs leads to a number of pathophysiological diseases causing malabsorption of nutrition and intestinal structure disruption, which may even contribute to systemic organ failure. Claudins are the major structural and functional components of TJs with at least 24 members in mammals. Claudins have distinct charge-selectivity, either by tightening the paracellular pathway or functioning as paracellular channels, regulating ions and small molecules passing through the paracellular pathway. In this review, we have discussed the functions of claudin family members, their distribution and localization in the intestinal tract of mammals, their alterations in intestine-related diseases and chemicals/agents that regulate the expression and localization of claudins as well as the intestinal permeability, which provide a therapeutic view for treating intestinal diseases.

ACF7 regulates colonic permeability

Colonic paracellular permeability is regulated by various factors, including dynamics of the cytoskeleton. Recently, ACF7 has been found to play a critical role in cytoskeletal dynamics as an essential integrator. To elucidate the physiological importance of ACF7 and paracellular permeability, we conditionally knocked out ACF7 in the intestinal mucosa of mice. Histopathological findings indicated that ACF7 deficiency resulted in significant interstitial proliferation and columnar epithelial cell rearrangement. Decreased colonic paracellular permeability was detected using a Ussing chamber and the FITC-inulin method. In order to clarify the underlying mechanism, we further analyzed the expression levels of three important tight junction proteins. Downregulation of ZO-1, occludin and claudin-1 was identified. Immunofluorescence provided strong evidence that ZO-1, occludin and claudin-1 were weakly stained. We hypothesized that ACF7 regulates cytoskeleton dynamics to alter mucosal epithelial arrangement and colonic paracellular permeability.

Evidence of oral translocation of anionic G6.5 dendrimers in mice

Development of carrier systems to improve oral bioavailability and target drugs to specific sites continues to be an unmet need. The goal of this study was to evaluate the potential of anionic generation (G) 6.5 poly(amido amine) (PAMAM) dendrimers in oral drug delivery by assessing their in vivo oral translocation. G6.5-COOH dendrimers were characterized for their physiochemical characteristics and acute oral toxicity was assessed in CD-1 mice. The dendrimers were labeled with (125)I and their stability evaluated. Oral bioavailability was assessed in the same mouse model. Investigation of the radioactivity profile in plasma revealed presence of both large and small molecular weight compounds. Detailed area under the curve analysis suggests an effective 9.4% bioavailability of radiolabeled marker associated with G6.5-COOH. Results reported here suggest the potential of dendrimers in permeating gastrointestinal barriers in vivo.

Effect of salvianolate on intestinal epithelium tight junction protein zonula occludens protein 1 in cirrhotic rats

AIM: To study the effect of salvianolate on tight junctions (TJs) and zonula occludens protein 1 (ZO-1) in small intestinal mucosa of cirrhotic rats.

METHODS: Cirrhosis was induced using carbon tetrachloride. Rats were randomly divided into the untreated group, low-dose salvianolate (12 mg/kg) treatment group, medium-dose salvianolate (24 mg/kg) treatment group, and high-dose salvianolate (48 mg/kg) treatment group, and were treated for 2 wk. Another 10 healthy rats served as the normal control group. Histological changes in liver tissue samples were observed under a light microscope. We evaluated morphologic indices of ileal mucosa including intestinal villi width and thickness of mucosa and intestinal wall using a pathological image analysis system. Ultrastructural changes in small intestinal mucosa were investigated in the five groups using transmission electron microscopy. The changes in ZO-1 expression, a tight junction protein, were analyzed by immunocytochemistry. The staining index was calculated as the product of the staining intensity score and the proportion of positive cells.

RESULTS: In the untreated group, hepatocytes showed a disordered arrangement, fatty degeneration was extensive, swelling was obvious, and disorganized lobules were divided by collagen fibers in hepatic tissue, which were partly improved in the salvianolate treated groups. In the untreated group, abundant lymphocytes infiltrated the fibrous tissue with proliferation of bile ducts, and collagen fibers gradually decreased and damaged hepatic lobules were partly repaired following salvianolate treatment. Compared with the untreated group, no differences in intestinal villi width between the five groups were observed. The villi height as well as mucosa and intestinal wall thickness gradually thickened with salvianolate treatment and were significantly shorter in the untreated group compared with those in the salvianolate treatment groups and normal group (P < 0.01). The number of microvilli decreased and showed irregular lengths and arrangements in the untreated group. The intercellular space between epithelial cells was wider. The TJs were discontinuous, which indicated disruption in TJ morphology in the untreated group. In the treated groups, the microvilli in the intestinal epithelium were regular and the TJs were gradually integrated and distinct. The expression of ZO-1 decreased in the small intestine of the untreated cirrhotic rats. The high expression rate of ZO-1 in ileal mucosa in the untreated group was significantly lower than that in the medium-dose salvianolate group (21.43% vs 64.29%, χ² = 5.25, P < 0.05), high-dose salvianolate group (21.43% vs 76.92%, χ² = 8.315, P < 0.01) and normal group (21.43% vs 90%, χ² = 10.98, P < 0.01).

CONCLUSION: Salvianolate improves liver histopathological changes, repairs intestinal mucosa and TJ structure, and enhances ZO-1 expression in the small intestinal mucosa in cirrhotic rats.

Connexin 26 facilitates gastrointestinal bacterial infection in vitro

Escherichia coli, including enteropathogenic E. coli (EPEC), represents the most common cause of diarrhoea worldwide and is therefore a serious public health burden. Treatment for gastrointestinal pathogens is hindered by the emergence of multiple antibiotic resistance, leading to the requirement for the development of new therapies. A variety of mechanisms act in combination to mediate gastrointestinal-bacterial-associated diarrhoea development. For example, EPEC infection of enterocytes induces attaching and effacing lesion formation and the disruption of tight junctions. An alternative enteric pathogen, Shigella flexneri, manipulates the expression of Connexin 26 (Cx26), a gap junction protein. S. flexneri can open Cx26 hemichannels allowing the release of ATP, whereas HeLa cells expressing mutant gap-junction-associated Cx26 are less susceptible to cellular invasion by S. flexneri than cells expressing wild-type (WT) Cx26. We have investigated further the link between Cx26 expression and gastrointestinal infection by using EPEC and S. flexneri as in vitro models of infection. In this study, a significant reduction in EPEC adherence was observed in cells expressing mutant Cx26 compared with WT Cx26. Furthermore, a significant reduction in both cellular invasion by S. flexneri and adherence by EPEC was demonstrated in human intestinal cell lines following treatment with Cx26 short interfering RNA. These in vitro results suggest that the loss of functional Cx26 expression provides improved protection against gastrointestinal bacterial pathogens. Thus, Cx26 represents a potential therapeutic target for gastrointestinal bacterial infection.

Non-systemic drugs: a critical review

Non-systemic drugs act within the intestinal lumen without reaching the systemic circulation. The first generation included polymeric resins that sequester phosphate ions, potassium ions, or bile acids for the treatment of electrolyte imbalances or hypercholesteremia. The field has evolved towards non-absorbable small molecules or peptides targeting luminal enzymes or transporters for the treatment of mineral metabolism disorders, diabetes, gastrointestinal (GI) disorders, and enteric infections. From a drug design and development perspective, non-systemic agents offer novel opportunities to address unmet medical needs while minimizing toxicity risks, but also present new challenges, including developing a better understanding and control of non-transcellular leakage pathways into the systemic circulation. The pharmacokinetic-pharmacodynamic relationship of drugs acting in the GI tract can be complex due to the variability of intestinal transit, interaction with chyme, and the complex environment of the surface epithelia. We review the main classes of nonabsorbable agents at various stages of development, and their therapeutic potential and limitations. The rapid progress in the identification of intestinal receptors and transporters, their functional characterization and role in metabolic and inflammatory disorders, will undoubtedly renew interest in the development of novel, safe, non-systemic therapeutics.

Side-stream smoking reduces intestinal inflammation and increases expression of tight junction proteins

AIM: To investigate the effect of side-stream smoking on gut microflora composition, intestinal inflammation and expression of tight junction proteins.

METHODS: C57BL/6 mice were exposed to side-stream cigarette smoking for one hour daily over eight weeks. Cecal contents were collected for microbial composition analysis. Large intestine was collected for immunoblotting and quantitative reverse transcriptase polymerase chain reaction analyses of the inflammatory pathway and tight junction proteins.

RESULTS: Side-stream smoking induced significant changes in the gut microbiota with increased mouse intestinal bacteria, Clostridium but decreased Fermicutes (Lactoccoci and Ruminococcus), Enterobacteriaceae family and Segmented filamentous baceteria compared to the control mice. Meanwhile, side-stream smoking inhibited the nuclear factor-κB pathway with reduced phosphorylation of p65 and IκBα, accompanied with unchanged mRNA expression of tumor necrosis factor-α or interleukin-6. The contents of tight junction proteins, claudin3 and ZO2 were up-regulated in the large intestine of mice exposed side-stream smoking. In addition, side-stream smoking increased c-Jun N-terminal kinase and p38 MAPK kinase signaling, while inhibiting AMP-activated protein kinase in the large intestine.

CONCLUSION: Side-stream smoking altered gut microflora composition and reduced the inflammatory response, which was associated with increased expression of tight junction proteins.

Mechanism and consequence of chitosan-mediated reversible epithelial tight junction opening

In order to increase the absorption of hydrophilic macromolecules in the small intestine, permeation enhancers such as chitosan (CS) and its derivatives have been evaluated. The aim of the current work was to investigate, on molecular levels, the effect of CS on tight junction (TJ) integrity in Caco-2 cells. The observed changes in transepithelial-electrical-resistance measurements and the staining patterns of the monolayer Caco-2 cells demonstrate that CS can transiently and reversibly open the TJs between cells, thus enhancing the paracellular permeability. TJ ultra-structures examined by transmission electron microscopy support the concept that CS did induce transient opening of TJs. We then assessed TJ disruption at the gene and protein expression levels. Our data indicate that exposure to CS followed by recovery resulted in a significant increase in claudin-4 (Cldn4) gene transcription. Additionally, CS treatment induced redistribution of the TJ protein CLDN4 intracellularly following by its degradation in lysosomes, which represented an important contributing factor in TJ weakening, leading to the opening of TJs. The recovery of TJ after CS disruption required CLDN4 protein synthesis. These results suggest that CS regulates TJs by inducing changes in transmembrane CLDN4 protein. Understanding the mechanism of interaction between CS and epithelial cells is of paramount importance and needs to be established to aid further development in the use of CS to mediate the trans-epithelial drug delivery.

Knockdown of aquaporin 3 is involved in intestinal barrier integrity impairment

AQP3 is a water/glycerol transporter expressed at the basolateral membrane of colonic epithelial cells. Although AQPs are expressed in the gastrointestinal tract, their effect on intestinal barrier has not been clear. Here, we showed that knockdown of AQP3 caused a dramatic, dose-dependent increase in E. coli C25 translocation, with the reduction of TEER and increasing LY permeability. Western blots revealed that expression of Claudin-1 and Occludin were significantly decreased in the AQP3 knockdown group, demonstrating that this treatment enhances paracellular permeability via an opening of the tight junction complex. These data not only describe the correlation between transcellular and paracellular pathways in human intestines, but also show that targeted knockdown of AQP3 might impair the intestinal barrier integrity.

Heregulin activation of ErbB2/ErbB3 signaling potentiates the integrity of airway epithelial barrier

BACKGROUND

Members of the ErbB family of the receptor protein tyrosine kinase superfamily mediate heregulin (HRG)-induced cell responses. Here we investigated HRG activation of ErbB receptors, and the role of this activation in the development of the permeability barrier in airway epithelial cells (AECs).

METHODS

Two airway epithelial-like cell lines, Calu-3 and 16HBE were exposed to HRG or no stimulus and were evaluated with respect to their paracellular permeability as determined by transepithelial electric resistance (TER) and fluorescein isothiocyanate (FITC)-dextran flux. Tight junctions (TJs) were assessed by immunocytochemical localization of occludin and zonula occludens-1.

RESULTS

HRG promoted the development of the permeability barrier and TJ formation by monolayers of Calu-3 and 16HBE cells. Calu-3 cells expressed ErbB1, ErbB2, and ErbB3, but not ErbB4, on their surface. ErbB3 knockdown by small interference RNA (siRNA) blunted the effects of HRG on the permeability barrier. ErbB3 is known as a kinase-dead receptor and relies on other members of the family for its phosphorylation. To identify its heterodimerization partner, we knocked down the expression of other ErbB family receptors. We found that HRG's effect on the permeability barrier could be significantly attenuated by transfecting cells with ErbB2 siRNA but not with EGFR siRNA.

CONCLUSION

These results indicate that HRG activation of ErbB2/ErbB3 heterodimers is essential for regulation of the permeability barrier in AECs.

Factors impacting corneal epithelial barrier function against Pseudomonas aeruginosa traversal

PURPOSE

Mechanisms determining epithelial resistance versus susceptibility to microbial traversal in vivo remain poorly understood. Here, a novel murine model was used to explore factors influencing the corneal epithelial barrier to Pseudomonas aeruginosa penetration.

METHODS

Murine corneas were blotted with tissue paper before inoculation with green fluorescent protein-expressing P. aeruginosa. The impact of blotting on epithelial integrity was evaluated by susceptibility to fluorescein staining and histology. Using fluorescence imaging, blotted corneas were compared to nonblotted corneas for susceptibility to bacterial binding and epithelial penetration after 5 hours or were monitored for disease development. In some experiments, inoculation was performed ex vivo to exclude tear fluid or corneas were pretreated with EGTA to disrupt Ca(2+)-dependent factors. The role of surfactant protein D (SP-D), which inhibits P. aeruginosa cell invasion in vitro, was examined using knockout mice.

RESULTS

Blotting enabled fluorescein penetration through the epithelium into the underlying stroma without obvious disruption to corneal morphology. Although blotting enabled bacterial binding to the otherwise adhesion-resistant epithelial surface, adherent bacteria did not penetrate the surface or initiate pathology. In contrast, bacteria penetrated blotted corneas after EGTA treatment and in SP-D knockouts. Visible disease occurred and progressed only in aged, blotted, and EGTA-treated, SP-D knockout mice.

CONCLUSIONS

Neither fluorescein staining nor bacterial adhesion necessarily predict or enable corneal susceptibility to bacterial penetration or disease. Corneal epithelial defenses limiting traversal by adherent bacteria include EGTA-sensitive factors and SP-D. Understanding mechanisms modulating epithelial traversal by microbes could improve our understanding of susceptibility to infection and may indicate new strategies for preventing disease.

Importance of disrupted intestinal barrier in inflammatory bowel diseases

The current paradigm of inflammatory bowel diseases (IBD), both Crohn's disease (CD) and ulcerative colitis (UC), involves the interaction between environmental factors in the intestinal lumen and inappropriate host immune responses in genetically predisposed individuals. The intestinal mucosal barrier has evolved to maintain a delicate balance between absorbing essential nutrients while preventing the entry and responding to harmful contents. In IBD, disruptions of essential elements of the intestinal barrier lead to permeability defects. These barrier defects exacerbate the underlying immune system, subsequently resulting in tissue damage. The epithelial phenotype in active IBD is very similar in CD and UC. It is characterized by increased secretion of chloride and water, leading to diarrhea, increased permeability via both the transcellular and paracellular routes, and increased apoptosis of epithelial cells. The main cytokine that seems to drive these changes is tumor necrosis factor alpha in CD, whereas interleukin (IL)-13 may be more important in UC. Therapeutic restoration of the mucosal barrier would provide protection and prevent antigenic overload due to intestinal "leakiness." Here we give an overview of the key players of the intestinal mucosal barrier and review the current literature from studies in humans and human systems on mechanisms underlying mucosal barrier dysfunction in IBD.