Active and passive involvement of claudins in the pathophysiology of intestinal inflammatory diseases

Role of Claudin- 3 as a biomarker of gut-skin axis integrity in patients with psoriasis

Increased intestinal permeability and gut dysbiosis are important factors in the pathophysiology of psoriasis and its associated conditions. Claudin-3 is a protein that is found in tight junctions and may be used to assess the integrity of the gut barrier. The aim of this study was to investigate serum concentration of Claudin- 3 (CLDN3) in patients with psoriasis. Exploring its possible relations with patients' demographic, clinical and laboratory findings was another objective. Fifty psoriatic patients and thirty-five age- and sex-matched healthy volunteers served as the study's control group in this case-control, hospital-based research. The amount of serum CLDN3 was determined by means of an enzyme-linked immunosorbent test (ELISA). Concentration of serum CLDN3 was found to be significantly higher in patients with psoriasis. (p = 0.002). There was no statistically significant correlation between CLDN3 and patient's clinical & laboratory variables. We demonstrated that gut permeability is dysfunctional in patients with psoriasis as indicated by reduction of serum CLDN3. Further investigations are needed to determine whether modulation of gut barrier may represent a new therapeutic approach for psoriasis.

Gut-brain barrier dysfunction bridge autistic-like behavior in mouse model of maternal separation stress: A behavioral, histopathological, and molecular study

Autism spectrum disorder (ASD) is a fast-growing neurodevelopmental disorder throughout the world. Experiencing early life stresses (ELS) like maternal separation (MS) is associated with autistic-like behaviors. It has been proposed that disturbance in the gut-brain axis-mediated psychiatric disorders following MS. The role of disruption in the integrity of gut-brain barrier in ASD remains unclear. Addressing this knowledge gap, in this study we aimed to investigate role of the gut-brain barrier integrity in mediating autistic-like behaviors in mouse models of MS stress. To do this, mice neonates are separated daily from their mothers from postnatal day (PND) 2 to PND 14 for 3 hours. During PND58-60, behavioral tests related to autistic-like behaviors including three-chamber sociability, shuttle box, and resident-intruder tests were performed. Then, prefrontal cortex (PFC), hippocampus, and colon samples were dissected out for histopathological and molecular evaluations. Results showed that MS is associated with impaired sociability and social preference indexes, aggressive behaviors, and impaired passive avoidance memory. The gene expression of CLDN1 decreased in the colon, and the gene expression of CLDN5, CLDN12, and MMP9 increased in the PFC of the MS mice. MS is associated with decrease in the diameter of CA1 and CA3 areas of the hippocampus. In addition, MS led to histopathological changes in the colon. We concluded that, probably, disturbance in the gut-brain barrier integrities mediated the autistic-like behavior in MS stress in mice.

Colonic Epithelial Permeability to Ions Is Restored after Vedolizumab Treatment and May Predict Clinical Response in Inflammatory Bowel Disease Patients

Vedolizumab (VDZ) is used for treating inflammatory bowel disease (IBD) patients. A study investigating colonic epithelial barrier function ex vivo following VDZ is lacking. This work aims to evaluate ex vivo the colonic epithelial barrier function in IBD patients at baseline and during VDZ treatment, and to investigate the relationships between barrier function and clinical parameters. Colonic specimens were obtained from 23 IBD patients before, and at 24 and 52 weeks after VDZ treatment, and from 26 healthy volunteers (HV). Transepithelial electrical resistance (TEER, permeability to ions) and paracellular permeability were measured in Ussing chambers. IBD patients showed increased epithelial permeability to ions (TEER, 13.80 ± 1.04 Ω × cm2 vs. HV 20.70 ± 1.52 Ω × cm2, p < 0.001) without changes in paracellular permeability of a 4 kDa probe. VDZ increased TEER (18.09 ± 1.44 Ω × cm2, p < 0.001) after 52 weeks. A clinical response was observed in 58% and 25% of patients at week 24, and in 62% and 50% at week 52, in ulcerative colitis and Crohn's disease, respectively. Clinical and endoscopic scores were strongly associated with TEER. TEER < 14.65 Ω × cm2 predicted response to VDZ (OR 11; CI 2-59). VDZ reduces the increased permeability to ions observed in the colonic epithelium of IBD patients before treatment, in parallel to a clinical, histological (inflammatory infiltrate), and endoscopic improvement. A low TEER predicts clinical response to VDZ therapy.

Time-dependent effects of tumor necrosis factor α on Ca2+-dependent secretion in murine small intestinal organoids

Background

Intestinal organoids are stem cell-derived, 3D "mini-guts" with similar functions as the native intestinal epithelium such as electrolyte transport or establishment of an epithelial barrier. During intestinal inflammation, epithelial functions are dysregulated by proinflammatory cytokines like tumor necrosis factor α (TNFα) and other messengers from the immune system resulting in a loss of electrolytes and water due to an impaired epithelial barrier and higher net secretion.

Methods

A murine small intestinal organoid model was established to study (long-term) effects of TNFα on the intestinal epithelium in vitro using live imaging, immunohistochemical staining and qPCR.

Results

TNFα induced apoptosis in intestinal organoids as indicated by an increased number of cells with immunoreactivity for cleaved caspase 3. Furthermore, TNFα exposure led to swelling of the organoids which was inhibited by bumetanide and was concomitant with an upregulation of the bumetanide-sensitive Na+-K+-2Cl- symporter 1 (NKCC1) as shown by qPCR. Fura-2 imaging experiments revealed time-dependent changes in Ca2+ signaling consisting of a rise in the basal cytosolic Ca2+ concentration at day 1 and an increase of the carbachol-induced Ca2+ response after 3 days TNFα exposure. This was prevented by preincubation with La3+, an inhibitor of non-selective cation channels, or by using a Ca2+-free buffer indicating an enhancement of the Ca2+ influx from the extracellular side by the cytokine. No significant changes in cDNA levels of epithelial barrier proteins could be observed in the presence of TNFα.

Conclusion

Intestinal organoids are a useful tool to study the mechanism underlying the TNFα-induced secretion on enterocytes such as the regulation of NKCC1 expression or the modulation of cellular Ca2+ signaling.

Chronic Stress Exposure Alters the Gut Barrier: Sex-Specific Effects on Microbiota and Jejunum Tight Junctions

Background

Major depressive disorder (MDD) is the leading cause of disability worldwide. Of individuals with MDD, 30% to 50% are unresponsive to common antidepressants, highlighting untapped causal biological mechanisms. Dysfunction in the microbiota-gut-brain axis has been implicated in MDD pathogenesis. Exposure to chronic stress disrupts blood-brain barrier integrity; still, little is known about intestinal barrier function in these conditions, particularly for the small intestine, where absorption of most foods and drugs takes place.

Methods

We investigated how chronic social or variable stress, two mouse models of depression, impact the jejunum intestinal barrier in males and females. Mice were subjected to stress paradigms followed by analysis of gene expression profiles of intestinal barrier-related targets, fecal microbial composition, and blood-based markers.

Results

Altered microbial populations and changes in gene expression of jejunum tight junctions were observed depending on the type and duration of stress, with sex-specific effects. We used machine learning to characterize in detail morphological tight junction properties, identifying a cluster of ruffled junctions in stressed animals. Junctional ruffling is associated with inflammation, so we evaluated whether lipopolysaccharide injection recapitulates stress-induced changes in the jejunum and observed profound sex differences. Finally, lipopolysaccharide-binding protein, a marker of gut barrier leakiness, was associated with stress vulnerability in mice, and translational value was confirmed on blood samples from women with MDD.

Conclusions

Our results provide evidence that chronic stress disrupts intestinal barrier homeostasis in conjunction with the manifestation of depressive-like behaviors in a sex-specific manner in mice and, possibly, in human depression.

Human organoids are superior to cell culture models for intestinal barrier research

Loss of intestinal epithelial barrier function is a hallmark in digestive tract inflammation. The detailed mechanisms remain unclear due to the lack of suitable cell-based models in barrier research. Here we performed a detailed functional characterization of human intestinal organoid cultures under different conditions with the aim to suggest an optimized ex-vivo model to further analyse inflammation-induced intestinal epithelial barrier dysfunction. Differentiated Caco2 cells as a traditional model for intestinal epithelial barrier research displayed mature barrier functions which were reduced after challenge with cytomix (TNFα, IFN-γ, IL-1ß) to mimic inflammatory conditions. Human intestinal organoids grown in culture medium were highly proliferative, displayed high levels of LGR5 with overall low rates of intercellular adhesion and immature barrier function resembling conditions usually found in intestinal crypts. WNT-depletion resulted in the differentiation of intestinal organoids with reduced LGR5 levels and upregulation of markers representing the presence of all cell types present along the crypt-villus axis. This was paralleled by barrier maturation with junctional proteins regularly distributed at the cell borders. Application of cytomix in immature human intestinal organoid cultures resulted in reduced barrier function that was accompanied with cell fragmentation, cell death and overall loss of junctional proteins, demonstrating a high susceptibility of the organoid culture to inflammatory stimuli. In differentiated organoid cultures, cytomix induced a hierarchical sequence of changes beginning with loss of cell adhesion, redistribution of junctional proteins from the cell border, protein degradation which was accompanied by loss of epithelial barrier function. Cell viability was observed to decrease with time but was preserved when initial barrier changes were evident. In summary, differentiated intestinal organoid cultures represent an optimized human ex-vivo model which allows a comprehensive reflection to the situation observed in patients with intestinal inflammation. Our data suggest a hierarchical sequence of inflammation-induced intestinal barrier dysfunction starting with loss of intercellular adhesion, followed by redistribution and loss of junctional proteins resulting in reduced barrier function with consecutive epithelial death.

Hermetia illucens Fermented with Lactobacillus plantarum KCCM12757P Alleviates Dextran Sodium Sulfate-Induced Colitis in Mice

Inflammatory bowel disease (IBD) can severely affect humans and animals and is difficult to treat. Black soldier fly (Hermetia illucens; Hi) larvae (BSFL) are a sustainable source of protein. However, no studies exist on the antioxidant and anti-inflammatory functions of BSFL or fermented BSFL with respect to IBD. In this study, riboflavin-producing Lactobacillus plantarum KCCM12757P was isolated from a fish farm tank, and in conjunction with hot water-extracted Hi (HeHi) (termed HeHi_Lp), was used to determine optimal fermentation conditions to increase vitamin B2 concentration. This in vivo study investigated the therapeutic effects and mechanistic role of HeHi_Lp in chronic colitis-induced murine models. Histological changes, inflammatory cytokine levels, and intestinal barrier function were explored. Gut microbial communities and gene expression in the nuclear factor (NF)-κB signaling pathway were also studied. HeHi_Lp remarkably reduced the disease activity index, inflammatory cytokine (inducible nitric oxide synthase, cyclooxygenase 2, tumor necrosis factor α, interleukin (IL-6 and IL-1β) levels, and increased body weight and colon length. HeHi_Lp administration significantly raised zonula occludens 1, occludin and claudin 1 and improved the composition of the gut microbiota and beneficial intestinal bacteria. These results suggest that HeHi_Lp can be used as a dietary supplement in pet food to alleviate colitis.

Mechanism of Acupuncture and Moxibustion on Promoting Mucosal Healing in Ulcerative Colitis

The latest guideline about ulcerative colitis (UC) clinical practice stresses that mucosal healing, rather than anti-inflammation, is the main target in UC clinical management. Current mucosal dysfunction mainly closely relates to the endoscopic intestinal wall (mechanical barrier) injury with the imbalance between intestinal epithelial cells (IECs) regeneration and death, as well as tight junction (TJ) dysfunction. It is suggested that biological barrier (gut microbiota), chemical barrier (mucus protein layer, MUC) and immune barrier (immune cells) all take part in the imbalance, leading to mechanical barrier injury. Lots of experimental studies reported that acupuncture and moxibustion on UC recovery by adjusting the gut microbiota, MUC and immune cells on multiple targets and pathways, which contributes to the balance of IEC regeneration and death, as well as TJ structure recovery in animals. Moreover, the validity and superiority of acupuncture and moxibustion were also demonstrated in clinic. This study aims to review the achievements of acupuncture and moxibustion on mucosal healing and analyse the underlying mechanisms.

Th22 cells and the intestinal mucosal barrier

T-helper 22 (Th22) cells represent a novel subset of CD4+ T cells that exhibit distinctive characteristics, namely the secretion of IL-22 while abstaining from secreting IL-17 and interferon-γ (IFN-γ). These cells serve as the primary source of IL-22, and both Th22 cells and IL-22 are believed to play a role in maintaining intestinal mucosal homeostasis in inflammatory bowel disease (IBD). However, the precise functions of Th22 cells and IL-22 in this context remain a subject of debate. In this work, we aimed to elucidate their impact on the integrity of the intestinal mucosal barrier by presenting an overview of the molecular structure characteristics and functional effects of Th22 cells and IL-22. Furthermore, we would explore targeted treatment approaches and potential therapeutic strategies focusing on the Th22 and IL-22 pathways.

Impaired intestinal permeability in patients with multiple sclerosis

BACKGROUND

A number of recent studies have shown that the intestinal microbiome, part of the brain-gut axis, is implicated in the pathophysiology of multiple sclerosis. An essential part of this axis, is the intestinal barrier and gastrointestinal disorders with intestinal barrier dysregulation appear to be linked to CNS demyelination, and hence involved in the etiopathogenesis of multiple sclerosis (MS).

OBJECTIVE

The aim of this study was to evaluate the integrity of the intestinal barrier in patients with clinically definite multiple sclerosis (CDMS) and clinically isolated syndrome (CIS) using two serum biomarkers, claudin-3 (CLDN3), a component of tight epithelial junctions, and intestinal fatty acid binding protein (I-FABP), a cytosolic protein in enterocytes.

METHODS

Serum levels of CLDN3 in 37 MS patients and 22 controls, and serum levels of I-FABP in 46 MS patients and 51 controls were measured using commercial ELISA kits. Complete laboratory tests excluded the presence of gluten-related disorders in all subjects. Thirty MS patients received either disease-modifying drugs (DMD), immunosuppression (IS) or corticosteroid treatment.

RESULTS

CLDN3 levels were only significantly higher in the MS patients treated with DMD or IS compared to the control group (P=0.006). There were no differences in I-FABP serum levels between the groups. Serum CLDN3 levels did not correlate with serum I-FABP levels in CDMS, in CIS patients or controls.

CONCLUSIONS

In multiple sclerosis patients, the intestinal epithelium may be impaired with increased permeability, but without significant enterocyte damage characterized by intracellular protein leakage. Based on our data, CLDN3 serum levels appear to assess intestinal dysfunction in MS patients but mainly in treated ones.

5-Aminosalicylic acid alters the gut microbiota and altered microbiota transmitted vertically to offspring have protective effects against colitis

Although many therapeutic options are available for inflammatory bowel disease (IBD), 5-aminosalicylic acid (5-ASA) is still the key medication, particularly for ulcerative colitis (UC). However, the mechanism of action of 5-ASA remains unclear. The intestinal microbiota plays an important role in the pathophysiology of IBD, and we hypothesized that 5-ASA alters the intestinal microbiota, which promotes the anti-inflammatory effect of 5-ASA. Because intestinal inflammation affects the gut microbiota and 5-ASA can change the severity of inflammation, assessing the impact of inflammation and 5-ASA on the gut microbiota is not feasible in a clinical study of patients with UC. Therefore, we undertook a translational study to demonstrate a causal link between 5-ASA administration and alterations of the intestinal microbiota. Furthermore, by rigorously controlling environmental confounders and excluding the effect of 5-ASA itself with a vertical transmission model, we observed that the gut microbiota altered by 5-ASA affected host mucosal immunity and decreased susceptibility to dextran sulfate sodium-induce colitis. Although the potential intergenerational transmission of epigenetic changes needs to be considered in this study, these findings suggested that alterations in the intestinal microbiota induced by 5-ASA directed the host immune system towards an anti-inflammatory state, which underlies the mechanism of 5-ASA efficacy.

cCPE Fusion Proteins as Molecular Probes to Detect Claudins and Tight Junction Dysregulation in Gastrointestinal Cell Lines, Tissue Explants and Patient-Derived Organoids

Claudins regulate paracellular permeability, contribute to epithelial polarization and are dysregulated during inflammation and carcinogenesis. Variants of the claudin-binding domain of Clostridium perfringens enterotoxin (cCPE) are highly sensitive protein ligands for generic detection of a broad spectrum of claudins. Here, we investigated the preferential binding of YFP- or GST-cCPE fusion proteins to non-junctional claudin molecules. Plate reader assays, flow cytometry and microscopy were used to assess the binding of YFP- or GST-cCPE to non-junctional claudins in multiple in vitro and ex vivo models of human and rat gastrointestinal epithelia and to monitor formation of a tight junction barrier. Furthermore, YFP-cCPE was used to probe expression, polar localization and dysregulation of claudins in patient-derived organoids generated from gastric dysplasia and gastric cancer. Live-cell imaging and immunocytochemistry revealed cell polarity and presence of tight junctions in glandular organoids (originating from intestinal-type gastric cancer and gastric dysplasia) and, in contrast, a disrupted diffusion barrier for granular organoids (originating from discohesive tumor areas). In sum, we report the use of cCPE fusion proteins as molecular probes to specifically and efficiently detect claudin expression, localization and tight junction dysregulation in cell lines, tissue explants and patient-derived organoids of the gastrointestinal tract.

Digested Cinnamon (Cinnamomum verum J. Presl) Bark Extract Modulates Claudin-2 Gene Expression and Protein Levels under TNFα/IL-1β Inflammatory Stimulus

Epigenetic changes, host-gut microbiota interactions, and environmental factors contribute to inflammatory bowel disease (IBD) onset and progression. A healthy lifestyle may help to slow down the chronic or remitting/relapsing intestinal tract inflammation characteristic of IBD. In this scenario, the employment of a nutritional strategy to prevent the onset or supplement disease therapies included functional food consumption. Its formulation consists of the addition of a phytoextract enriched in bioactive molecules. A good candidate as an ingredient is the Cinnamon verum aqueous extract. Indeed, this extract, subjected to a process of gastrointestinal digestion simulation (INFOGEST), exhibits beneficial antioxidant and anti-inflammatory properties in an in vitro model of the inflamed intestinal barrier. Here, we deepen the study of the mechanisms related to the effect of digested cinnamon extract pre-treatment, showing a correlation between transepithelial electrical resistance (TEER) decrement and alterations in claudin-2 expression under Tumor necrosis factor-α/Interleukin-1β (TNF-α/IL-1) β cytokine administration. Our results show that pre-treatment with cinnamon extract prevents TEER loss by claudin-2 protein level regulation, influencing both gene transcription and autophagy-mediated degradation. Hence, cinnamon polyphenols and their metabolites probably work as mediators in gene regulation and receptor/pathway activation, leading to an adaptive response against renewed insults.

The Clinical Significance of Serum Biomarkers of the Intestinal Barrier in Systemic Sclerosis: A Cross-Sectional Study

Systemic sclerosis (SSc) is an immune-mediated connective tissue disease. Recent studies reported differences in the composition of intestinal microbiota (dysbiosis) in patients with SSc compared to nonsclerodermic subjects. Dysbiosis may disrupt the intestinal barrier, which leads to immunological activation via microbial antigen and metabolite translocation. The study aimed to assess the differences in intestinal permeability between SSc patients and controls and to examine the correlation between intestinal permeability and complications of SSc. The study comprised 50 patients with SSc and 30 matched subjects. Serum intestinal permeability markers: intestinal fatty acid binding protein, claudin-3, and lipopolysaccharides (LPS) were determined using an enzyme-linked immunosorbent assay. SSc patients had a significantly increased concentration of LPS compared to control subjects (232.30 [149.00-347.70] versus 161.00 [83.92-252.20] pg/mL, p < 0.05). The patients with shorter SSc duration (≤6 years) had an increased concentration of LPS and claudin-3 compared to the subgroup with longer disease length: LPS (280.75 [167.30-403.40] versus 186.00 [98.12-275.90] pg/mL, p < 0.05), and claudin-3 (16.99 [12.41-39.59] versus 13.54 [10.29-15.47] ng/mL, p < 0.05). The patients with esophageal dysmotility had a decreased LPS level compared to those without this complication (188.05 [102.31-264.40] versus 283.95 [203.20-356.30] pg/mL, p < 0.05). Increased intestinal permeability in SSc may exacerbate the course of the disease and increase the risk of developing complications. Lower LPS levels in SSc might be a hallmark of esophageal dysmotility.

Adequacy of Iodine Status and Associations with Gut Health: A Prospective Cohort Study among Infants in 8 Low- and Middle-Income Countries

BACKGROUND

Environmental enteric dysfunction increases the likelihood of micronutrient deficiencies among infants, but few studies have assessed the potential impact of gut health on urinary iodine concentration (UIC) among this vulnerable group.

OBJECTIVES

We describe the trends of iodine status among infants from 6 to 24 mo old and examine the associations between intestinal permeability, inflammation, and UIC from 6 to 15 mo of age.

METHODS

Data from 1557 children enrolled in this birth cohort study conducted in 8 sites were included in these analyses. UIC was measured at 6, 15, and 24 mo of age by using the Sandell-Kolthoff technique. Gut inflammation and permeability were assessed using the concentrations of fecal neopterin (NEO), myeloperoxidase (MPO) and alpha-1-antitrypsin (AAT), and lactulose-mannitol ratio (LM). A multinomial regression analysis was used to assess the classified UIC (deficiency or excess). Linear mixed regression was used to test the effect of interactions among biomarkers on logUIC.

RESULTS

All studied populations had adequate (≥100 μg/L) to excess (≥371 μg/L) median UIC at 6 mo. Between 6 and 24 mo, 5 sites displayed a significant decline in the infant's median UIC. However, median UIC remained within the optimal range. An increase of NEO and MPO concentrations by +1 unit in ln scale reduced the risk of low UIC by 0.87 (95% CI: 0.78-0.97) and 0.86 (95% CI: 0.77-0.95), respectively. AAT moderated the association between NEO and UIC (P < 0.0001). The shape of this association appears to be asymmetric and in a reverse J-shape, with a higher UIC observed at both lower NEO and AAT concentrations.

CONCLUSIONS

Excess UIC was frequent at 6 mo and tended to normalize at 24 mo. Aspects of gut inflammation and increased permeability appear to reduce the prevalence of low UIC in children aged 6 to 15 mo. Programs addressing iodine-related health should consider the role of gut permeability in vulnerable individuals.

Kynurenine pathway metabolites modulated the comorbidity of IBD and depressive symptoms through the immune response

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is defined as chronic inflammation in the gastrointestinal tract. Notably, more than 20% of people with IBD experience depressive symptoms. Understanding the immunological mechanism of chronic intestinal inflammation on cognitive behavior has become a key research focus. Previous studies have shown that a dysregulated immune response contributes to chronic inflammation and depressive symptoms. The tolerant phenotype exhibited by immune cells regulates the course of chronic inflammation in distinct ways. In addition, neuroglia, such as microglia and astrocytes specific to the brain, are also influenced by deregulated inflammation to mediate the development of depressive symptoms. The kynurenine pathway (KP), a significant tryptophan metabolic pathway, transforms tryptophan into a series of KP metabolites that modulate chronic inflammation and depressive symptoms. In particular, indoleamine 2,3-dioxygenase 1 (IDO1), a rate-limiting enzyme in the KP, is activated by chronic inflammation and leads to the production of kynurenine. In addition, disruption of the brain-gut axis induced by IBD allows kynurenine to cross the blood-brain barrier (BBB) and form a series of neuroactive kynurenine metabolites in glial cells. Among them, quinolinic acid continuously accumulates in the brain, indicating depression. Thus, KP metabolites are critical for driving the comorbidity of IBD and depressive symptoms. In this review, the pathological mechanism of KP metabolite-mediated chronic intestinal inflammation and depressive symptoms by regulating the immune response is summarized according to the latest reports.

Claudin-3 is a novel intestinal integrity marker in patients with alopecia areata: Correlation with the disease severity

BACKGROUND

The development of alopecia areata is suggested to be influenced by intestinal permeability and gut dysbiosis. Claudin-3, an essential component of tight junctions which may act as an indicator of intestinal barrier integrity.

AIMS

The study's objective was to evaluate the plasma concentration level of Claudin-3 in alopecia areata patients and its relationship to the severity of the condition.

PATIENTS AND METHODS

In this case-control study, 50 alopecia areata patients and 30 healthy age and sex controls were involved. An enzyme-linked immunosorbent assay was used to determine the concentration of claudin-3 in the blood.

RESULTS

Patients with alopecia areata had significantly higher plasma claudin-3 concentrations than healthy controls [median (interquartile range), 7.73 ng/ml (4.49-33.7) vs. 6.14 ng/ml (4.45-15.6), p < 0.005]. Positive relations were found between claudin-3 and SALT score (r = 0.675 & p-value < 0.001).

CONCLUSIONS

Claudin-3, a gut permeability biomarker, is elevated in alopecia areata and correlates with disease severity.

Assessing the in vivo ameliorative effects of Lactobacillus acidophilus KLDS1.0901 for induced non-alcoholic fatty liver disease treatment

Reputed as a significant metabolic disorder, non-alcoholic fatty liver disease (NAFLD) is characterized by high-fat deposits in the liver and causes substantial economic challenges to any country's workforce. Previous studies have indicated that some lactic acid bacteria may effectively prevent or treat NAFLD. Overall, L. acidophilus KLDS1.0901 protected against HFD-induced NAFLD by improving liver characteristics and modulating microbiota composition, and thus could be a candidate for improving NAFLD. This study aimed to assess the protective effects of L. acidophilus KLDS1.0901 on a high-fat diet(HFD)-induced NAFLD. First, hepatic lipid profile and histological alterations were determined to study whether L. acidophilus KLDS1.0901 could ameliorate NAFLD. Then, the intestinal permeability and gut barrier were explored. Finally, gut microbiota was analyzed to elucidate the mechanism from the insights of the gut-liver axis. The results showed that Lactobacillus KLDS1.0901 administration significantly decreased body weight, Lee's index body, fat rate, and liver index. L. acidophilus KLDS1.0901 administration significantly improved lipid profiles by decreasing the hepatic levels of total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) and by increasing the high-density lipoprotein cholesterol (HDL-C) levels. A conspicuous decrease of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in serum was observed after L. acidophilus KLDS1.0901 administration. Meanwhile, the H&E and Oil Red O-stained staining showed that L. acidophilus KLDS1.0901 significantly reduced liver lipid accumulation of HFD-fed mice by decreasing the NAS score and lipid area per total area. Our results showed that L. acidophilus KLDS1.0901 administration decreased the interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α) concentrations accompanied by the increase of interleukin-10 (IL-10). L. acidophilus KLDS1.0901 administration could improve the intestinal barrier function by upregulating the mRNA levels of occludin, claudin-1, ZO-1, and Muc-2, which were coupled to the decreases of the concentration of LPS and D-lactic acid. Notably, L. acidophilus KLDS1.0901 administration modulated the gut microbiota to a near-normal pattern. Hence, our results suggested that L. acidophilus KLDS1.0901 can be used as a candidate to ameliorate NAFLD.

Selective Role of TNFα and IL10 in Regulation of Barrier Properties of the Colon in DMH-Induced Tumor and Healthy Rats

Recently it has been reported that the tumor adjacent colon tissues of 1,2-dymethylhydrazine induced (DMH)-rats revealed a high paracellular permeability. We hypothesized that the changes might be induced by cytokines. Colorectal cancer is accompanied by an increase in tumor necrosis factor alpha (TNFα) and interleukin 10 (IL10) that exert opposite regulatory effects on barrier properties of the colon, which is characterized by morphological and functional segmental heterogeneity. The aim of this study was to analyze the level of TNFα and IL10 in the colon segments of DMH-rats and to investigate their effects on barrier properties of the proximal and distal parts of the colon in healthy rats. Enzyme immunoassay analysis showed decreased TNFα in tumors in the distal part of the colon and increased IL10 in proximal tumors and in non-tumor tissues. Four-hour intraluminal exposure of the colon of healthy rats with cytokines showed reduced colon barrier function dependent on the cytokine: TNFα decreased it mainly in the distal part of the colon, whereas IL10 decreased it only in the proximal part. Western blot analysis revealed a more pronounced influence of IL10 on tight junction (TJ) proteins expression by down-regulation of the TJ proteins claudin-1, -2 and -4, and up-regulation of occludin only in the proximal part of the colon. These data may indicate a selective role of the cytokines in regulation of the barrier properties of the colon and a prominent role of IL10 in carcinogenesis in its proximal part.

Metagenomic evidence for increasing antibiotic resistance in progeny upon parental antibiotic exposure as the cost of hormesis

Antibiotics are widely consumed in the intensive mariculture industry. A better understanding of the effect of antibiotics on intergenerational antibiotic resistance in organisms is urgent since intergenerational transmission is crucial for the spread of antibiotic resistance genes (ARGs) in the environment. Herein, marine medaka (Oryzias melastigma) chronically exposed to low doses of sulfamethazine (SMZ) hormetically affected the progeny, characterized by increased richness and diversity of fecal microbiota and intestinal barrier-related gene up-regulation. Progeny immunity was modulated and caused by genetic factors due to the absence of significant SMZ accumulation in F1 embryos. In addition, some of the top genera in the progeny were positively correlated with immune diseases, while the expression of some immune-related genes, such as TNFα, IL1R2, and TLR3 changed significantly. This further indicated that the host selection caused by changes in progeny immunity was probably the primary determinant of progeny intestinal microbial colonization. Metagenomic analysis revealed that Proteobacteria represented the primary carriers of ARGs, while parental SMZ exposure facilitated the distribution and enrichment of multiple ARGs involved in the antibiotic inactivation in the progeny by promoting the diversity of Gammaproteobacteria and Bacteroidetes, further illustrating that antibiotic selection pressure persisted even if the offspring were not exposed. Therefore, SMZ induced hormesis in the progeny at the expense of increasing antibiotic resistance. Collectively, these findings provide a comprehensive overview of the intergenerational effect of antibiotics and serve as a reminder that the ARG transmission induced by the intergenerational impact of antibiotics on organisms should not be ignored.

Mast cells disrupt the duodenal mucosal integrity: Implications for the mechanisms of barrier dysfunction in functional dyspepsia

BACKGROUND

Functional dyspepsia (FD) is a common functional gastrointestinal (GI) disorder, but its pathophysiology is poorly understood. Mast cells (MCs) may play a critical role in the development of FD. Therefore, the aim of this study was to investigate the effect of MCs on barrier function, tight junction (TJ) proteins and related signaling pathways.

METHODS

The expression of the TJ proteins claudin-8, ZO-1 and occludin in biopsy tissues from seven FD patients and five controls was assessed. Based on the in vivo results, we further investigated the effect of (1) MC degranulation in a coculture model of Caco-2/RBL-2H3 cells and tryptase in Caco-2 monolayers, (2) MC degranulation in the presence or absence of a PAR-2 antagonist and (3) MC degranulation in the presence or absence of an ERK1/2 signaling pathway inhibitor. The epithelial integrity of Caco-2 cell monolayers was assessed by measuring the transepithelial electrical resistance (TEER). The expression of TJ proteins was evaluated by western blotting, QT-PCR and immunostaining.

RESULTS

Epithelial claudin-8, ZO-1 and occludin protein expression were significantly reduced in tissues from FD patients compared with controls. MC degranulation and tryptase decreased the TEER and reduced the expression of TJ proteins in Caco-2 cell monolayers. A PAR-2 antagonist and an ERK1/2 signaling pathway inhibitor significantly reduced the effect of MC degranulation on the TEER and TJ protein expression in Caco-2 cell monolayers.

CONCLUSIONS

MCs disrupt duodenal barrier function by modulating the levels of TJ proteins, and the PAR-2 and ERK1/2 signaling pathways may mediate the pathogenesis of FD.

A one month high fat diet disrupts the gut microbiome and integrity of the colon inducing adiposity and behavioral despair in male Sprague Dawley rats

High-fat diet (HFD) is associated with gut microbiome dysfunction and mental disorders. However, the time-dependence as to when this occurs is unclear. We hypothesized that a short-term HFD causes colonic tissue integrity changes resulting in behavioral changes. Rats were fed HFD or low-fat diet (LFD) for a month and gut microbiome, colon, and behavior were evaluated. Behavioral despair was found in the HFD group. Although obesity was absent, the HFD group showed increased percent weight gain, epididymal fat tissue, and leptin expression. Moreover, the HFD group had increased colonic damage, decreased expression of the tight junction proteins, and higher lipopolysaccharides (LPS) in serum. Metagenomic analysis revealed that the HFD group had more Bacteroides and less S24-7 which correlated with the decreased claudin-5. Finally, HFD group showed an increase of microglia percent area, increased astrocytic projections, and decreased phospho-mTOR. In conclusion, HFD consumption in a short period is still sufficient to disrupt gut integrity resulting in LPS infiltration, alterations in the brain, and behavioral despair even in the absence of obesity.

In vivo evidence of the prevents DSS-induced colitis of Lactiplantibacillus plantarum L15

Ulcerative colitis (UC) is challenging to treat and severely impacts patients and families. A previous study reported immunomodulatory and reduction of pro-inflammatory properties for the Lactiplantibacillus plantarum L15. This study aimed to analyze the preventive properties and mechanistic actions in an in vivo colitis model. The histopathological alteration, inflammation cytokines, and intestinal barrier function were analyzed. Subsequently, the cecal gut microbiota contents and products from different groups were detected. Finally, gene expressions related to the NF-κB signaling process were evaluated. L. plantarum L15 significantly decreased disease activity index (DAI), myeloperoxidase activity (MPO), pro-inflammatory cytokine (TNF-α, IL-1β, and IL-6) level, and increased weight change, colon length, and production of inflammation-suppressing cytokines. Furthermore, this strain supplementation substantially increased ZO-1, Occludin, and Claudin-1, and MUC2 mRNA expression levels with a corresponding decrease in serum lipopolysaccharide and D-lactic acid contents. In addition, L. plantarum L15 improved gut microbiota composition and increased short-chain fatty acid (SCFAs) in the colon content, which significantly reduced the transfer of NF-κB p65 to the nucleus. Our findings provide a theoretical basis for L. plantarum L15 as a preventive candidate for UC.

Barrier Perturbation in Porcine Peyer’s Patches by Tumor Necrosis Factor is Associated With a Dysregulation of Claudins

The proinflammatory cytokine tumor necrosis factor (TNF) has been described as one of the main mediators of intestinal inflammatory diseases, affecting the composition of tight junction (TJ) proteins and leading to a disruption of the epithelial barrier. An intact intestinal barrier is mandatory, because the follicle-associated epithelium of Peyer’s patches represents the first defense line of the intestinal immune system and ensures a controlled uptake of antigens from the gut lumen. In the current study, we have analyzed the detailed effects of TNF on the follicle-associated epithelium of porcine Peyer’s patches by applying the Ussing chamber technique. Epithelial tissue specimens of Peyer’s patches and the surrounding villus epithelium were mounted into conventional Ussing chambers and incubated with TNF for 10 h. The transepithelial resistance, representing epithelial barrier function of the tissue, was recorded. A reduction of transepithelial resistance was detected after 8 h in Peyer’s patch tissue specimens, whereas the villus epithelium was not significantly affected by TNF. Subsequent molecular analysis of TJ protein expression revealed a marked decrease of claudin-1 and -4, and an increase of claudin-2. In neighboring villus epithelium, no significant changes in the expression of TJ proteins could be shown. A strong increase of TNF receptor-2 (TNFR-2) could also be detected in Peyer’s patches, in agreement with the major role of this receptor in Peyer’s patches. Our findings were in accordance with changes detected by confocal laser scanning immunofluorescence microscopy. The regulation of TNF effects via myosin light chain kinase (MLCK) was analyzed in blocking experiments. Our detailed analysis is the first to show that TNF affects the barrier function of the follicle-associated epithelium of porcine Peyer’s patches but has no effects on the villus epithelium. These findings reveal not only the basic differences of epithelial barrier function between the two structures, but also the significance of Peyer’s patches as a primary mucosal immune defense.

Tight junctions: from molecules to gastrointestinal diseases

Intestinal epithelium functions as a tissue barrier to prevent interaction between the internal compartment and the external milieu. Intestinal barrier function also determines epithelial polarity for the absorption of nutrients and the secretion of waste products. These vital functions require strong integrity of tight junction proteins. In fact, intestinal tight junctions that seal the paracellular space can restrict mucosal-to-serosal transport of hostile luminal contents. Tight junctions can form both an absolute barrier and a paracellular ion channel. Although defective tight junctions potentially lead to compromised intestinal barrier and the development and progression of gastrointestinal (GI) diseases, no FDA-approved therapies that recover the epithelial tight junction barrier are currently available in clinical practice. Here, we discuss the impacts and regulatory mechanisms of tight junction disruption in the gut and related diseases. We also provide an overview of potential therapeutic targets to restore the epithelial tight junction barrier in the GI tract.

Micronutrient Improvement of Epithelial Barrier Function in Various Disease States: A Case for Adjuvant Therapy

The published literature makes a very strong case that a wide range of disease morbidity associates with and may in part be due to epithelial barrier leak. An equally large body of published literature substantiates that a diverse group of micronutrients can reduce barrier leak across a wide array of epithelial tissue types, stemming from both cell culture as well as animal and human tissue models. Conversely, micronutrient deficiencies can exacerbate both barrier leak and morbidity. Focusing on zinc, Vitamin A and Vitamin D, this review shows that at concentrations above RDA levels but well below toxicity limits, these micronutrients can induce cell- and tissue-specific molecular-level changes in tight junctional complexes (and by other mechanisms) that reduce barrier leak. An opportunity now exists in critical care—but also medical prophylactic and therapeutic care in general—to consider implementation of select micronutrients at elevated dosages as adjuvant therapeutics in a variety of disease management. This consideration is particularly pointed amidst the COVID-19 pandemic.

Hypermethylation of miR-145 promoter-mediated SOX9-CLDN8 pathway regulates intestinal mucosal barrier in Crohn's disease

Background

Intestinal barrier impairment plays an essential role in the pathogenesis of Crohn's disease (CD), and claudins (CLDNs) dysfunction contributes to intestinal mucosa injury. SOX9, an important transcription factor, is upregulated in the disease-affected colon of patients with CD; however, its precise role in CD remains largely unknown. Our aim was to explore the interaction between SOX9 and CLDNs, and further elucidate the underlying mechanisms in CD.

Methods

SOX9 expression in patients with CD was evaluated using quantitative polymerase chain reaction, immunoblotting, and immunohistochemistry. The regulatory relationship between SOX9 and CLDNs was analyzed via a dual-luciferase reporter assay, chromatin immunoprecipitation, overexpression, and RNA interference methods. MicroRNAs (miRNAs) involved in the SOX9-CLDN pathway were predicted with bioinformatics analysis, and the upstream molecular mechanism was interpreted using MassARRAY methylation detection.

Findings

Upregulated expression of SOX9 in the disease-affected intestine mucosa was identified in both patients with CD and mice challenged with trinitrobenzene sulfonic acid (TNBS). SOX9 negatively regulated the expression of CLDN8, accompanying reduced intestinal permeability. MiR-145-5p downregulation was found in patients with CD and TNBS-induced colitis mice owing to an aberrant miR-145 promoter hypermethylation, which subsequently interfered the SOX9-CLDN8 pathway. MiR-145-5p agomir treatment alleviated TNBS-induced colitis in wild-type mice by inhibiting Sox9 expression and restoring Cldn8 expression, whereas similar findings were not apparent in the Cldn8^−/− mice.

Interpretation

SOX9 mediates the crosstalk between upstream miR-145-5p and downstream CLDN8, and further impairs intestinal mucosal barrier homeostasis in CD. Targeting the miR-145-5p/SOX9/CLDN8 pathway represents a promising therapeutic strategy for CD.

Funding

The National Natural Science Foundation of China (#81870374, #81670498, #81630018, #82070538, #8210031148), the Guangdong Science and Technology (#2017A030306021, #2020A1515111087), the Guangzhou Science and Technology Department (#202002030041), and the Fundamental Research Funds for the Central Universities (#19ykzd11).

Therapeutic effect of baicalin on inflammatory bowel disease: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Baicalin (BI) is an important biologically active flavonoid isolated from the root of Scutellaria radix (Huang Qin). Traditionally Scutellaria radix was the common drug of dysentery. As the main flavonoid compound, there is a distribution tendency of baicalin to the intestinal tract and it has a protective effect on the gastrointestinal tract.

AIM OF THE REVIEW

This review aims to compile up-to-date and comprehensive information on the efficacy of baicalin in vitro and in vivo, about treating inflammatory bowel disease. Relevant information on the therapeutic potential of baicalin against inflammatory bowel disease was collected from the Web of Science, Pubmed and so on. Additionally, a few books and magazines were also consulted to get the important information.

RESULTS

The mechanisms of baicalin against inflammatory bowel disease mainly include anti-inflammation, antioxidant, immune regulation, maintenance of intestinal barrier, maintenance of intestinal flora balance. Also, BI can relieve parts of extraintestinal manifestations (EIMs), and prevent colorectal cancer.

CONCLUSION

Baicalin determined the promising therapeutic prospects as potential supplementary medicines for the treatment of IBD.

IL-1β and the Intestinal Epithelial Tight Junction Barrier

The intestinal epithelial tight junction (TJ) barrier controls the paracellular permeation of contents from the intestinal lumen into the intestinal tissue and systemic circulation. A defective intestinal TJ barrier has been implicated as an important pathogenic factor in inflammatory diseases of the gut including Crohn's disease, ulcerative colitis, necrotizing enterocolitis, and celiac disease. Previous studies have shown that pro-inflammatory cytokines, which are produced during intestinal inflammation, including interleukin-1β (IL-1β), tumor necrosis factor-α, and interferon-γ, have important intestinal TJ barrier-modulating actions. Recent studies have shown that the IL-1β-induced increase in intestinal TJ permeability is an important contributing factor of intestinal inflammation. The IL-1β-induced increase in intestinal TJ permeability is mediated by regulatory signaling pathways and activation of nuclear transcription factor nuclear factor-κB, myosin light chain kinase gene activation, and post-transcriptional occludin gene modulation by microRNA and contributes to the intestinal inflammatory process. In this review, the regulatory role of IL-1β on intestinal TJ barrier, the intracellular mechanisms that mediate the IL-1β modulation of intestinal TJ permeability, and the potential therapeutic targeting of the TJ barrier are discussed.

Bacterial Translocation Associates With Aggression in Schizophrenia Inpatients

Objective: Accumulating evidence indicates that inflammation abnormalities may contribute to aggression behaviors in psychotic patients, however, the possible sources of inflammation remain elusive. We aimed to evaluate the associations among aggression, inflammation, and bacterial translocation (BT) in aggression-affected schizophrenia (ScZ) inpatients with 2 weeks of antipsychotics discontinuation.

Methods: Serum specimens collected from 112 aggression and 112 non-aggression individuals with ScZ and 56 healthy adults were used for quantifications of inflammation- or BT-related biomarkers. Aggression severity was assessed by Modified Overt Aggression Scale (MOAS).

Results: Proinflammation phenotype dominated and leaky gut-induced BT occurred only in cases with ScZ with a history of aggression, and the MOAS score positively related to levels of C-reactive protein, interleukin (IL)-6, IL-1β, and tumor necrosis factor-α. Furthermore, serum levels of BT-derived lipopolysaccharide (LPS), as well as LPS-responded soluble CD14, were not only positively correlated with levels of above proinflammation mediators but also the total MOAS score and subscore for aggression against objects or others.

Conclusion: Our results collectively demonstrate the presence of leaky gut and further correlate BT-derived LPS and soluble CD14 to onset or severity of aggression possibly by driving proinflammation response in inpatients with ScZ, which indicates that BT may be a novel anti-inflammation therapeutic target for aggression prophylaxis.

Impact of the ileal microbiota on colon cancer

Besides tumor cell-intrinsic oncogenic pathways, host and environmental factors have a major impact on cancer immunosurveillance and the efficacy of immunotherapeutics. Several modalities of anticancer treatments including immunogenic chemotherapies and immune checkpoint inhibitors lose their efficacy in patients treated with broad-spectrum antibiotics, pointing to a key role for the gut microbiota. The complex interactions between intestinal microbes, gut immunity and anti-tumor responses constitute an emerging field of investigation. In this work, we revise key primary literature, with an emphasis on recent mechanistic insights, unraveling the interplay between the immunosurveillance of colon cancers and ileal factors including the local microbiota, tissue architecture and immune system.

Alleviative Effects of Exopolysaccharide Produced by Lactobacillus helveticus KLDS1.8701 on Dextran Sulfate Sodium-Induced Colitis in Mice

Ulcerative colitis (UC) is a non-specific chronic inflammatory disease with lesions located in the colon and rectum. The aim of this study was to evaluate the anti-inflammatory effects of exopolysaccharide-1 (EPS-1) isolated by L. helveticus KLDS1.8701 on UC. The anti-inflammatory effects of EPS-1 were studied using dextran sulphate sodium (DSS)-induced UC model. In vivo results showed that EPS-1 administration significantly ameliorated weight loss, colon shortening, disease activity index (DAI) score, myeloperoxidase (MPO) activity, and colon tissue damage. In addition, EPS-1 administration significantly decreased the levels of pro-inflammatory cytokines and increased levels of anti-inflammatory cytokines. Meanwhile, EPS-1 administration significantly up-regulated the expression of tight junction proteins and mucin. Furthermore, EPS-1 administration modulated gut microbiota composition caused by DSS and increased the short-chain fatty acids (SCFAs) levels. Collectively, our study showed the alleviative effects of EPS- isolated by L. helveticus KLDS1.8701 on DSS-induced UC via alleviating intestinal inflammation, improving mucosal barrier function, and modulating gut microbiota composition.

Long-term dual antiplatelet-induced intestinal injury resulting in translocation of intestinal bacteria into blood circulation increased the incidence of adverse events after PCI in patients with coronary artery disease

BACKGROUND AND AIMS

The present study aimed to investigate the efficacy and safety of long-term (>18 months) dual antiplatelet therapy (DAPT) after percutaneous coronary intervention (PCI).

METHODS

A total of 3205 coronary artery disease (CAD) patients after PCI from CORFCHD-PCI, a retrospective cohort study (Identifier: ChiCTR-ORC-16010153), were divided into two groups: monotherapy of aspirin or clopidogrel group (SAPT group, n = 2188 and DAPT group, n = 1017) according to whether to discontinue DAPT 18 months after PCI. After propensity matching analysis (PSM), we included 1017 patients in the DAPT group and 1017 patients in the SAPT group. All the patients were followed-up for at least 18 months and the longest follow-up time is 120 months. The primary endpoint was the incidence of major adverse cardiac events (MACEs). The secondary endpoints were the incidence of major adverse cardiovascular and cerebrovascular events (MACEEs) and bleeding events. We also selected 178 patients for detection of claudin-3 and intestinal fatty acid-binding protein and 58 patients for 16s RNA sequencing of whole blood.

RESULTS

The incidences of MACEs (13.9% vs. 9.0%, p = 0.001) and MACCEs (16.3% vs.10.0%, p < 0.001) were significantly increased in the DAPT group compared to the SAPT group. We also found DAPT increased the bleeding events compared to SAPT (4.6% vs. 2.9%, p = 0.048). Multivariate Cox regression analyses showed that in the DAPT group, cumulative risk of MACCEs increased 1.797 times (HR = 1.797, 95%CI: 1.429-2.226, p < 0.001), MACEs increased 1.737 times (HR = 1.737, 95%CI: 1.360-2.218, p < 0.001) and the bleeding events increased 2.129 times (HR = 2.129, 95%CI: 1.388-3.266, p = 0.001) compared to the SAPT group. We also found the plasma concentrations of claudin-3 and intestinal fatty acid-binding protein (I-FABP) were significantly higher in patients in the DAPT group compared with patients in the SAPT group (both p < 0.001). Correspondingly, the abundance of blood intestinal bacteria in the DAPT group was significantly increased compared to that in the SAPT group (p < 0.001). Furthermore, high-throughput metabolomics analysis suggested that serum level of ceramide (d18:1/16:0) and Neu5Ac was significantly increased in the DAPT group compared to the SAPT group (both p < 0.001).

CONCLUSIONS

The present study suggests that long-term dual antiplatelet therapy longer than 18 months significantly increases the incidence of both ischemic events and bleeding events after PCI. This preliminary study also indicates that long-term DAPT causes intestinal injury, which induces translocation of intestinal bacteria into the bloodstream.

Immune-Mediated Aggravation of the Campylobacter concisus-Induced Epithelial Barrier Dysfunction

Campylobacter concisus is a human-pathogenic bacterium of the gastrointestinal tract. This study aimed at the contribution of the mucosal immune system in the context of intestinal epithelial barrier dysfunction induced by C. concisus. As an experimental leaky gut model, we used in vitro co-cultures of colonic epithelial cell monolayers (HT-29/B6-GR/MR) with M1-macrophage-like THP-1 cells on the basal side. Forty-eight hours after C. concisus infection, the decrease in the transepithelial electrical resistance in cell monolayers was more pronounced in co-culture condition and 22 ± 2% (p < 0.001) higher than the monoculture condition without THP-1 cells. Concomitantly, we observed a reduction in the expression of the tight junction proteins occludin and tricellulin. We also detected a profound increase in 4 kDa FITC-dextran permeability in C. concisus-infected cell monolayers only in co-culture conditions. This is explained by loss of tricellulin from tricellular tight junctions (tTJs) after C. concisus infection. As an underlying mechanism, we observed an inflammatory response after C. concisus infection through pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) released from THP-1 cells in the co-culture condition. In conclusion, the activation of subepithelial immune cells exacerbates colonic epithelial barrier dysfunction by C. concisus through tricellulin disruption in tTJs, leading to increased antigen permeability (leaky gut concept).

Claudin-2 pore causes leak that breaches the dam in intestinal inflammation

The tight junction protein claudin-2 is upregulated in inflammatory bowel disease, and yet its deficit worsens infectious and chemical colitis. In this issue of the JCI, Raju and Shashikanth et al. examined the contribution of claudin-2 to immune-mediated colitis. The authors used transgenic mouse models to show that claudin-2 deficiency attenuated colitis progression as well as a leak barrier defect, albeit at the risk of intestinal obstruction. Further, inhibition of claudin-2 by targeting casein kinase 2 (CK2) also ameliorated colitis. The findings reveal unsuspected links between the pore and leak pathways of intestinal permeability and immune responses leading to colitis. They additionally suggest potential targets for therapeutic intervention in inflammatory bowel disease.

Tumor necrosis factor-α induces claudin-3 upregulation in kidney tubular epithelial cells through NF-κB and CREB1

Claudins are essential for tight junction formation and paracellular transport, and they affect key cellular events including proliferation and migration. The properties of tight junctions are dynamically modulated by a variety of inputs. We previously showed that the inflammatory cytokine tumor necrosis factor-α (TNFα), a major pathogenic factor in kidney disease, alters epithelial permeability by affecting the expression of claudin-1, -2, and -4 in kidney tubular cells. Here, we explored the effect of TNFα on claudin-3 (Cldn-3), a ubiquitous barrier-forming protein. We found that TNFα elevated Cldn-3 protein expression in tubular epithelial cells (LLC-PK1 and IMCD3) as early as 3 h post treatment. Bafilomycin A and bortezomib, inhibitors of lysosomal and proteasomes, respectively, reduced Cldn-3 degradation. However, TNFα caused a strong upregulation of Cldn-3 in the presence of bafilomycin, suggesting an effect independent from lysosomes. Blocking protein synthesis using cycloheximide prevented Cldn-3 upregulation by TNFα, verifying the contribution of de novo Cldn-3 synthesis. Indeed, TNFα elevated Cldn-3 mRNA levels at early time points. Using pharmacological inhibitors and siRNA-mediated silencing, we determined that the effect of TNFα on Cldn-3 was mediated by extracellular signal regulated kinase (ERK)-dependent activation of NF-κB and PKA-induced activation of CREB1. These two pathways were turned on by TNFα in parallel and both were required for the upregulation of Cldn-3. Because Cldn-3 was suggested to modulate cell migration and epithelial-mesenchymal transition (EMT), and TNFα was shown to affect these processes, Cldn-3 upregulation may modulate regeneration of the tubules following injury.

Histone H3K9 methylation regulates chronic stress and IL-6-induced colon epithelial permeability and visceral pain

BACKGROUND

Chronic stress is associated with activation of the HPA axis, elevation in pro-inflammatory cytokines, decrease in intestinal epithelial cell tight junction (TJ) proteins, and enhanced visceral pain. It is unknown whether epigenetic regulatory pathways play a role in chronic stress-induced intestinal barrier dysfunction and visceral hyperalgesia.

METHODS

Young adult male rats were subjected to water avoidance stress ± H3K9 methylation inhibitors or siRNAs. Visceral pain response was assessed. Differentiated Caco-2/BBE cells and human colonoids were treated with cortisol or IL-6 ± antagonists. Expression of TJ, IL-6, and H3K9 methylation status at gene promoters was measured. Transepithelial electrical resistance and FITC-dextran permeability were evaluated.

KEY RESULTS

Chronic stress induced IL-6 up-regulation prior to a decrease in TJ proteins in the rat colon. The IL-6 level inversely correlated with occludin expression. Treatment with IL-6 decreased occludin and induced visceral hyperalgesia. Chronic stress and IL-6 increased H3K9 methylation and decreased transcriptional GR binding to the occludin gene promoter, leading to down-regulation of protein expression and increase in paracellular permeability. Intrarectal administration of a H3K9 methylation antagonist prevented chronic stress-induced visceral hyperalgesia in the rat. In a human colonoid model, cortisol decreased occludin expression, which was prevented by the GR antagonist RU486, and IL-6 increased H3K9 methylation and decreased TJ protein levels, which were prevented by inhibitors of H3K9 methylation.

CONCLUSIONS & INFERENCES

Our findings support a novel role for methylation of the repressive histone H3K9 to regulate chronic stress, pro-inflammatory cytokine-mediated reduction in colon TJ protein levels, and increase in paracellular permeability and visceral hyperalgesia.

The Intestinal Barrier and Current Techniques for the Assessment of Gut Permeability

The intestinal barrier is essential in human health and constitutes the interface between the outside and the internal milieu of the body. A functional intestinal barrier allows absorption of nutrients and fluids but simultaneously prevents harmful substances like toxins and bacteria from crossing the intestinal epithelium and reaching the body. An altered intestinal permeability, a sign of a perturbed barrier function, has during the last decade been associated with several chronic conditions, including diseases originating in the gastrointestinal tract but also diseases such as Alzheimer and Parkinson disease. This has led to an intensified interest from researchers with diverse backgrounds to perform functional studies of the intestinal barrier in different conditions. Intestinal permeability is defined as the passage of a solute through a simple membrane and can be measured by recording the passage of permeability markers over the epithelium via the paracellular or the transcellular route. The methodological tools to investigate the gut barrier function are rapidly expanding and new methodological approaches are being developed. Here we outline and discuss, in vivo, in vitro and ex vivo techniques and how these methods can be utilized for thorough investigation of the intestinal barrier.

Channel functions of claudins in the organization of biological systems

Claudins are tight junction proteins mostly appreciated in their function of paracellular barrier-formation. Compared to a virtual absence of any tight junctions, their paracellular sealing role certainly stands out. Yet, it was recognized immediately after the discovery of the first claudins, that some members of the claudin protein family were able to convey size and charge selectivity to the paracellular pathway. Thus, paracellular permeability can be fine-tuned according to the physiological needs of a tissue by inserting these channel-forming claudins into tight junction strands. Precise permeability adjustment is further suggested by the presence of numerous isoforms of channel-forming claudins (claudin-10b-, -15-, -16-like isoforms) in various vertebrate taxa. Moreover, their expression and localization are controlled by multiple transcriptional and posttranslational mechanisms. Consequently, mutation or dysregulation of channel-forming claudins can cause severe diseases. The present review therefore aims at providing an up-to-date report of the current research on these aspects of channel-forming claudins and their possible implications on future developments.

Protective effect of emodin on intestinal epithelial tight junction barrier integrity in rats with sepsis induced by cecal ligation and puncture

The present study investigated the protective effects of emodin on intestinal epithelial tight junction (TJ) barrier integrity in cecal ligation and puncture (CLP)-induced septic rats and its possible mechanisms of action. Healthy male Sprague-Dawley rats were randomly divided into three groups (n=20 per group): Sham group, CLP group and CLP + emodin group. Animals were sacrificed at 12 and 24 h after the model was established. Abdominal aortic blood and specimens of the ileum were harvested for analysis. The histopathological changes in intestinal mucosa and the ultrastructures of intestinal epithelial cells were investigated using light microscopy and transmission electron microscopy. The integrity of the intestinal barrier was assessed by examining plasma diamine oxidase (DAO) levels and the ratio of urine lactulose to mannitol (L/M). The levels of the intestinal TJ proteins claudin-3, zonula occludens (ZO)-1 and occludin were detected using immunohistochemistry, western blotting and reverse transcription-quantitative PCR. The results showed that the pathological damage to intestinal mucosa and the intestinal tissue injury score in the CLP + emodin group were significantly reduced compared to those of the CLP group, and the differences were more obvious at 24 h compared with 12 h. DAO activity and the L/M ratio in the emodin pre-treatment group decreased significantly at 24 h compared with the CLP groups. The protein and mRNA levels of the TJ proteins claudin-3, ZO-1 and occludin in the emodin pre-treatment groups at 12 and 24 h were increased, while occludin mRNA level was found to be decreased compared with the CLP groups. The present study suggested that emodin may significantly reduce the damage to the intestinal epithelial barrier in sepsis, inhibit intestinal barrier permeability and protect intestinal barrier integrity. Emodin may protect intestinal barrier integrity by elevating expression levels of the TJ proteins claudin-3, ZO-1 and occludin in CLP rats.

Contribution of pithelial poptosis and ubepithelial mmune esponses in Campylobacter jejuni-nduced arrier isruption

Campylobacter jejuni is a widespread zoonotic pathogen and the leading bacterial cause of foodborne gastroenteritis in humans. Previous infection studies showed disruption of intercellular contacts, induction of epithelial apoptosis, and immune activation, all three contributing to intestinal barrier dysfunction leading to diarrhea. The present study aims to determine the impact of subepithelial immune cells on intestinal barrier dysfunction during Campylobacter jejuni infection and the underlying pathological mechanisms. Infection was performed in a co-culture of confluent monolayers of the human colon cell line HT-29/B6-GR/MR and THP-1 immune cells. Twenty-two hours after infection, transepithelial electrical resistance (TER) was decreased by 58 ± 6% compared to controls. The infection resulted in an increase in permeability for fluorescein (332 Da; 4.5-fold) and for FITC-dextran (4 kDa; 3.5-fold), respectively. In contrast, incubation of the co-culture with the pan-caspase inhibitor Q-VD-OPh during the infection resulted in a complete recovery of the decrease in TER and a normalization of flux values. Fluorescence microscopy showed apoptotic fragmentation in infected cell monolayers resulting in a 5-fold increase of the apoptotic ratio, accompanied by an increased caspase-3 cleavage and caspase-3/7 activity, which both were not present after Q-VD-OPh treatment. Western blot analysis revealed increased claudin-1 and claudin-2 protein expression. Inhibition of apoptosis induction did not normalize these tight junction changes. TNFα concentration was increased during the infection in the co-culture. In conclusion, Campylobacter jejuni infection and the consequent subepithelial immune activation cause intestinal barrier dysfunction mainly through caspase-3-dependent epithelial apoptosis. Concomitant tight junction changes were caspase-independent. Anti-apoptotic and immune-modulatory substances appear to be promising agents for treatment of campylobacteriosis.

Mechanisms underlying reduced weight gain in intestinal fatty acid-binding protein (IFABP) null mice

Intestinal-fatty acid binding protein (IFABP; FABP2) is a 15-kDa intracellular protein abundantly present in the cytosol of the small intestinal (SI) enterocyte. High-fat (HF) feeding of IFABP-/- mice resulted in reduced weight gain and fat mass relative to wild-type (WT) mice. Here, we examined intestinal properties that may underlie the observed lean phenotype of high fat-fed IFABP-/- mice. No alterations in fecal lipid content were found, suggesting that the IFABP-/- mice are not malabsorbing dietary fat. However, the total excreted fecal mass, normalized to food intake, was increased for the IFABP-/- mice relative to WT mice. Moreover, intestinal transit time was more rapid in the IFABP-/- mice. IFABP-/- mice displayed a shortened average villus length, a thinner muscularis layer, reduced goblet cell density, and reduced Paneth cell abundance. The number of proliferating cells in the crypts of IFABP-/- mice did not differ from that of WT mice, suggesting that the blunt villi phenotype is not due to alterations in proliferation. IFABP-/- mice were observed to have altered expression of genes and proteins related to intestinal structure, while immunohistochemical analyses revealed increased staining for markers of inflammation. Taken together, these studies indicate that the ablation of IFABP, coupled with high-fat feeding, leads to changes in gut motility and morphology, which likely contribute to the relatively leaner phenotype occurring at the whole-body level. Thus, IFABP is likely involved in dietary lipid sensing and signaling, influencing intestinal motility, intestinal structure, and nutrient absorption, thereby impacting systemic energy metabolism.NEW & NOTEWORTHY Intestinal fatty acid binding protein (IFABP) is thought to be essential for the efficient uptake and trafficking of dietary fatty acids. In this study, we demonstrate that high-fat-fed IFABP-/- mice have an increased fecal output and are likely malabsorbing other nutrients in addition to lipid. Furthermore, we observe that the ablation of IFABP leads to marked alterations in intestinal morphology and secretory cell abundance.

Protective effects of iridoid glycosides on acute colitis via inhibition of the inflammatory response mediated by the STAT3/NF-кB pathway

Morroniside and loganin are iridoid glycosides extracted from Cornus officinalis, a plant species widely used in traditional Chinese medicine. However, the anti-inflammatory effects of morroniside and loganin in colitis are barely understood. The aim of the present study was to explore the effects of morroniside and loganin on the dextran sodium sulfate (DSS)-induced murine model of colitis and an LPS-induced colorectal cancer (CRC) cell inflammation model, and to clarify the underlying mechanisms. We found that morroniside and loganin were able to ameliorate clinical features, including disease activity index (DAI), histological inflammation score and periodic acid-Schiff staining (PAS). In the mouse model, morroniside and loganin treatment increased expression of tight junction proteins (TJs) and decreased pro-inflammatory cytokine production. Moreover, our findings showed that the expression of p-STAT3 and p-p65 were suppressed compared to the disease group. In in vitro experiments, treatment with morroniside and loganin had no obvious effects on proliferative activity in HCT116 cells and HIEC-6 cells. Expression of pro-inflammatory cytokines was inhibited by morroniside and loganin treatment in comparison with the LPS-treated group. Taken together, morroniside and loganin have beneficial effects on colitis in vivo and are anti-inflammatory in vitro. Possible mechanisms of the anti-inflammatory response may include blockade of the STAT3/NF-κB pathway.

The Effects of Flavomycin and Colistin Sulfate Pre-Treatment on Ileal Bacterial Community Composition, the Response to Salmonella typhimurium and Host Gene Expression in Broiler Chickens

The composition of the bacterial community affects the intestinal health and growth performance of broiler chickens. The main purpose of this study was to explore the effects of flavomycin and colistin sulfate on the resistance to Salmonella typhimurium infection, ileal bacteria and intestinal health. In total, 396 1-day-old broiler chickens were randomly divided into six groups. Two groups were fed each one of the diets-the control diet (CON), the flavomycin at 10 mg/kg diet (AntiG+), and the colistin sulfate at 40 mg/kg diet (AntiG-), for 5 days. Then, one of each of the two groups was challenged with S. typhimurium on the 8th day; these were named CONS, AntiG+S and AntiG-S, respectively. The results showed that S. typhimurium significantly reduced the feed intake and body weight gain, and increased the feed conversion ratio (p < 0.05). It also increased the inflammatory expressions of NF-κB and MyD88 genes (p < 0.05); and reduced the expressions of claudin-1, occludin and mucin-2 (p < 0.05) tight junction genes in the intestines. S. typhimurium significantly reduced ileal bacterial diversity indexes of observed-species, chao1 and Shannon (p < 0.05). Compared with AntiG+S group, AntiG-S group increased the body weight gain of broiler chickens (p < 0.05), reduced the expression of inflammatory genes (p < 0.05) and intestinal permeability to fluorescein isothiocyanate (p < 0.05). AntiG-S group also improved the ileal bacterial diversity indexes of observed-species and Shannon (p < 0.05). There were many significant correlations between intestinal bacteria, intestinal gene expressions and intestinal morphology (p < 0.05). This study indicated that pre-constructed AntiG- bacteria could against a S. typhimurium infection by inhibiting the expressions of intestinal inflammation genes and increasing the diversity of intestinal bacteria.

Claudin-2: Roles beyond Permeability Functions

Claudin-2 is expressed in the tight junctions of leaky epithelia, where it forms cation-selective and water permeable paracellular channels. Its abundance is under fine control by a complex signaling network that affects both its synthesis and turnover in response to various environmental inputs. Claudin-2 expression is dysregulated in many pathologies including cancer, inflammation, and fibrosis. Claudin-2 has a key role in energy-efficient ion and water transport in the proximal tubules of the kidneys and in the gut. Importantly, strong evidence now also supports a role for this protein as a modulator of vital cellular events relevant to diseases. Signaling pathways that are overactivated in diseases can alter claudin-2 expression, and a good correlation exists between disease stage and claudin-2 abundance. Further, loss- and gain-of-function studies showed that primary changes in claudin-2 expression impact vital cellular processes such as proliferation, migration, and cell fate determination. These effects appear to be mediated by alterations in key signaling pathways. The specific mechanisms linking claudin-2 to these changes remain poorly understood, but adapters binding to the intracellular portion of claudin-2 may play a key role. Thus, dysregulation of claudin-2 may contribute to the generation, maintenance, and/or progression of diseases through both permeability-dependent and -independent mechanisms. The aim of this review is to provide an overview of the properties, regulation, and functions of claudin-2, with a special emphasis on its signal-modulating effects and possible role in diseases.

Claudin-2 suppresses GEF-H1, RHOA, and MRTF, thereby impacting proliferation and profibrotic phenotype of tubular cells

The tight junctional pore-forming protein claudin-2 (CLDN-2) mediates paracellular Na⁺ and water transport in leaky epithelia and alters cancer cell proliferation. Previously, we reported that tumor necrosis factor-α time-dependently alters CLDN-2 expression in tubular epithelial cells. Here, we found a similar expression pattern in a mouse kidney injury model (unilateral ureteral obstruction), consisting of an initial increase followed by a drop in CLDN-2 protein expression. CLDN-2 silencing in LLC-PK¹ tubular cells induced activation and phosphorylation of guanine nucleotide exchange factor H1 (GEF-H1), leading to Ras homolog family member A (RHOA) activation. Silencing of other claudins had no such effects, and re-expression of an siRNA-resistant CLDN-2 prevented RHOA activation, indicating specific effects of CLDN-2 on RHOA. Moreover, kidneys from CLDN-2 knockout mice had elevated levels of active RHOA. Of note, CLDN-2 silencing reduced LLC-PK1 cell proliferation and elevated expression of cyclin-dependent kinase inhibitor P27 (P27KIP1) in a GEF-H1/RHOA-dependent manner. P27KIP1 silencing abrogated the effects of CLDN-2 depletion on proliferation. CLDN-2 loss also activated myocardin-related transcription factor (MRTF), a fibrogenic RHOA effector, and elevated expression of connective tissue growth factor and smooth muscle actin. Finally, CLDN-2 down-regulation contributed to RHOA activation and smooth muscle actin expression induced by prolonged tumor necrosis factor-α treatment, because they were mitigated by re-expression of CLDN-2. Our results indicate that CLDN-2 suppresses GEF-H1/RHOA. CLDN-2 down-regulation, for example, by inflammation, can reduce proliferation and promote MRTF activation through RHOA. These findings suggest that the initial CLDN-2 elevation might aid epithelial regeneration, and CLDN-2 loss could contribute to fibrotic reprogramming.

Cell Adhesion Structures in Epithelial Cells Are Formed in Dynamic and Cooperative Ways

There are many morphologically distinct membrane structures with different functions at the surface of epithelial cells. Among these, adherens junctions (AJ) and tight junctions (TJ) are responsible for the mechanical linkage of epithelial cells and epithelial barrier function, respectively. In the process of new cell-cell adhesion formation between two epithelial cells, such as after wounding, AJ form first and then TJ form on the apical side of AJ. This process is very complicated because AJ formation triggers drastic changes in the organization of actin cytoskeleton, the activity of Rho family of small GTPases, and the lipid composition of the plasma membrane, all of which are required for subsequent TJ formation. In this review, the authors focus on the relationship between AJ and TJ as a representative example of specialization of plasma membrane regions and introduce recent findings on how AJ formation promotes the subsequent formation of TJ.

Impact of Sensitization and Inflammation on the Interaction of Mast Cells With the Intestinal Epithelium in Rats

The density of intestinal mast cells has been reported to increase during inflammatory bowel disease (IBD). As mast cell mediators are known to increase the permeability of epithelial tight junctions, we hypothesized that antigen responses in sensitized animals might be enhanced under inflammatory conditions. This would contribute to a vicious circle by further enhancing the entry of luminal antigens into the colonic wall and thereby continuing the inadequate immune response during IBD. Therefore, one group of rats was sensitized against ovalbumin. In a second group of animals additionally a colitis was induced by rectal administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) dissolved in ethanol. Specimens from distal colon and jejunum (as intestinal segment located distantly from the inflamed area) were mounted in Ussing chambers to measure tissue conductance, short-circuit current (I_sc) induced by antigen exposure and paracellular permeability (fluorescein flux). This was paralleled by determination of mast cell markers and tight junction proteins with immunofluorescence and qPCR. In contrast to the initial hypothesis, antigen-induced I_sc was not upregulated, but tended to be downregulated in the tissues from the colitis animals, both in colon and in jejunum. Only in the jejunum mast cell degranulation evoked an increase in fluorescein flux. Mast cell density was not altered significantly in the colon of the colitis animals. In the jejunum, sensitization induced a strong increase in mast cell density, which was unaffected by additional induction of colitis. Expression of sealing tight junction components claudin-3 and -4 were increased on the protein level in the sensitized animals in comparison to non-sensitized animals. Additional induction of colitis evoked a downregulation of claudin-3 in both intestinal segments and an upregulation of claudin-4 in the jejunum. Consequently, these data indicate segment differences in mast cell - epithelium interaction, but no enhancement of ion secretion in the TNBS/ethanol model of acute colitis after prior sensitization.

Spondyloarthritis patients with and without intestinal symptoms - searching for discriminating biomarkers

Spondyloarthritis (SpA) is often complicated with subclinical gut inflammation. This study was aimed at searching for biomarkers discriminating SpA patients with and without intestinal symptoms. A group of 29 SpA patients and 33 healthy volunteers (control) were included in the study. Based on clinical evaluation, the patient cohort was subdivided into two groups: 1) SpA accompanied by various intestinal symptoms suggesting gut inflammation (group 2, n = 14) and 2) without such complications (group 1, n = 15). Serum concentrations of interleukins (IL) (IL-10, IL-17A/F, IL-22, IL-23), tumour necrosis factor (TNF), bone-homeostasis-related factors (osteoprotegerin – OPG and Dickkopf-1 – DKK-1), and the concentrations of selected gut inflammation-associated factors (intestinal fatty acid binding protein – iFABP, claudin 3 – CLDN3 and calprotectin) in samples of sera and/or urine or stool, respectively, were measured by specific ELISA. Serum concentrations of tested factors were similar in SpA patients and control. Faecal calprotectin level was higher in patients but did not discriminate between group 1 and 2. Compared to group 1, group 2 was characterized by elevated erythrocyte sedimentation rate (ESR), higher serum CLDN3 and DKK-1 levels. In SpA patients, serum DKK-1 concentrations correlated with systemic inflammation markers (R = 0.6, p < 0.01), while serum CLDN3 was found to be an independent risk factor (OR = 4.5, p = 0.021) for the occurrence of intestinal symptoms. We conclude that in SpA patients, up-regulated circulating levels of CLDN3 seem to be related to intestinal complication, while the quantity of circulating DKK-1 reflects the intensity of systemic inflammation.