Establishment of Intestinal Epithelial Cell Monolayers and Their Use in Calcium Switch Assay for Assessment of Intestinal Tight Junction Assembly

Inhibition of TRPV1 attenuates innate nasal epithelial responses via NF-κB signaling pathway in allergic rhinitis

OBJECTIVES

Nasal epithelial cells initiate innate responses to allergens by releasing IL-1 family cytokines, such as IL-33, and disrupting the mucosal barrier. TRPV1 has gained increasing recognition for its role in immune modulation in allergic conditions. This study aimed to elucidate the mechanisms by which epithelial cells detect allergens and explore the pivotal role of TRPV1 in regulating innate nasal epithelial responses.

METHODS

To identify TRPV1-related genes and pathways, the GSE167225 dataset was analyzed. To validate TRPV1 expression, clinical data and nasal tissues from 34 patients with AR and 13 controls were collected. To further investigate its mechanisms, OVA-sensitized C57BL/6 mice were exposed to the TRPV1 antagonist SB-705498, and TRPV1 knockout mice were utilized. Primary human nasal epithelial cells were used for in vitro experiments, and various assays, including reverse transcription polymerase chain reaction(RT-PCR), western blotting(WB), and others, were performed to assess gene expression and signaling pathways.

RESULTS

Bioinformatics and clinical analysis revealed elevated TRPV1 expression in patients with AR, positively correlated with nasal itching and sneezing severity(R = 0.6493, P < 0.001; R = 0.4906, P < 0.001). In vivo, SB-705498 and TRPV1 ablation significantly alleviated allergy symptoms, reduced allergen-induced IL-33 release, and prevented disruption of tight junction protein occludin in murine models. In vitro, TRPV1 antagonism suppressed capsaicin-induced calcium influx, NF-κB activation, and IL-33 overexpression.

CONCLUSIONS

Allergen exposure enhances the secretion of IL-33 in hNECs via the TRPV1-NF-κB pathway, thus compromising epithelial tight junction integrity. Inhibition of TRPV1 can attenuate the effects of allergen-induced innate nasal epithelial responses. Our study offers novel insights into the potential therapeutic targeting of TRPV1 in AR.

Poliprotect®, a Medical Device Made of Substances, Potently Protects the Human Esophageal Mucosa Challenged by Multiple Agents: Evidence from In Vitro and Ex Vivo Electrophysiological Models

The integrity of esophageal epithelial cells in patients with gastroesophageal reflux disease (GERD) or GERD-like symptoms is the first mechanism of protection to decrease the sensitivity to gastric reflux and heartburn symptoms. We investigated the protective effects of Poliprotect® (PPRO), a CE-marked medical device, on esophageal epithelial integrity using in vitro and ex vivo models. In vitro, the protective effects of PPRO were tested on Caco-2 cells. PPRO demonstrated safety and protection against oxidative damage induced by hydrogen peroxide. It also preserved epithelial integrity by maintaining transepithelial electrical resistance (TEER) against damage from calcium removal or bile acid exposure (taurodeoxycholic acid, TDCA). Ex vivo, esophageal biopsies from patients subjected to endoscopy were mounted in Ussing chambers and exposed to damaging agents (HCl or HCl + TDCA). Untreated biopsies (control) showed significant loss of epithelial resistance (up to -33%). In contrast, low concentrations of PPRO (50-100 µg/mL) provided strong protection against these damages (p < 0.001), even after 60 min of washing. Histological analysis confirmed the barrier-enhancing effect of PPRO. Overall, PPRO effectively protected the esophageal epithelium from damage in both models, suggesting its potential role in alleviating GERD or GERD-like symptoms by strengthening mucosal barriers and reducing epithelial sensitivity to reflux.

Enhanced intestinal epithelial co-culture model with orbital mechanical stimulation: a proof-of-concept application in food nanotoxicology

Introduction

Current in vitro intestinal models lack the mechanical forces present in the physiological environment, limiting their reliability for nanotoxicology studies. Here, we developed an enhanced Caco-2/HT29-MTX-E12 co-culture model incorporating orbital mechanical stimulation to better replicate intestinal conditions and investigate nanoparticle interactions.

Methods

We established co-cultures under static and dynamic conditions, evaluating their development through multiple approaches including barrier integrity measurements, gene expression analysis, and confocal microscopy. We introduced novel quantitative analysis of dome formation as a differentiation marker and demonstrated the model application by investigating cellular responses to titanium dioxide (TiO₂) nanoparticles in a digested food matrix.

Results

Dynamic conditions accelerated epithelial differentiation, achieving functional barrier properties by day 14 rather than day 21, with enhanced mucin production and more organized three-dimensional structure. Mechanical stimulation selectively promoted goblet cell differentiation without affecting general epithelial markers. The optimized model successfully detected concentration-dependent oxidative stress responses to TiO₂ exposure, revealing cellular dysfunction preceding membrane damage.

Discussion

This improved co-culture system provides a better physiological platform for nanotoxicology studies. By incorporating mechanical forces, each cell type exhibits more representative behavior, creating a more realistic experimental setup. The model bridges the gap between simple monocultures and complex 3D systems, offering a practical approach for investigating nanoparticle-epithelium interactions in a food-relevant context.

Solanum melongena L. Extract Promotes Intestinal Tight Junction Re-Assembly via SIRT-1-Dependent Mechanisms

Tight junction disruption can lead to pathogenesis of various diseases without therapeutic strategy to recover intestinal barrier integrity. The main objective of this study is to demonstrate the effect of Solanum melongena L. extract (SMLE) on intestinal tight junction recovery and its underlying mechanism. Intestinal barrier function is attenuated by Ca2+ depletion. SMLE treatment increased TER value across T84 cell monolayers. Permeability assay reveals that Ca2+ depletion promotes 4-kDa FITC-dextran permeability, but not 70-kDa FITC-dextran. SMLE suppresses the rate of 4-kDa FITC-dextran permeability, indicating that SMLE inhibits paracellular leak pathway permeability. SMLE-mediated TER increase and leak pathway suppression are abolished by neither calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ) inhibitor nor AMP-activated protein kinase (AMPK) inhibitor. Furthermore, mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK) inhibitors have no effects on SMLE-mediated TER increase and leak pathway suppression. Interestingly, SMLE is unable to enhance TER value and diminish leak pathway permeability in T84 cell monolayers pre-treated with sirtuin-1 (SIRT-1) inhibitor. Immunofluorescence staining reveals that SMLE enhances re-assembly of tight junction proteins, including occludin and ZO-1 to intercellular space but this effect is abolished by SIRT-1 inhibitor. These data suggest that SMLE promotes intestinal tight junction re-assembly via SIRT-1-dependent manner.

Intestinal epithelial differentiation and barrier function is promoted in vitro by a Cynara cardunculus L. leaf extract through AMPK pathway activation

Gut epithelial barrier perturbation leads to leaky gut syndrome and permeation of substances activating immune response. Polyphenols can improve intestinal barrier function and represent candidates for preventing development of leaky gut. Herein, we evaluated in vitro the molecular mechanisms involved in the protective effects of a polyphenol-rich extract from leaves of Cynara cardunculus L. (CCLE) on intestinal barrier function and integrity on Caco-2 human epithelial cells. Treatment with CCLE from seeding until complete differentiation improved intestinal function by increasing trans-epithelial electrical resistance (TEER), reducing paracellular permeability to fluorescein, and promoting faster recovery of tight junctions (TJ) assembly in the Ca2+ switch assay. CCLE stimulated epithelial cell differentiation inducing alkaline phosphatase activity and TJ proteins. These CCLE-induced effects were attributed to activation of AMP-activated protein kinase (AMPK) pathway. Our data support the use of Cynara cardunculus L. leaves, an agricultural co-product rich in bioactive polyphenols, for the health of intestinal epithelium.

Integration of multiple flexible electrodes for real-time detection of barrier formation with spatial resolution in a gut-on-chip system

In healthy individuals, the intestinal epithelium forms a tight barrier to prevent gut bacteria from reaching blood circulation. To study the effect of probiotics, dietary compounds and drugs on gut barrier formation and disruption, human gut epithelial and bacterial cells can be cocultured in an in vitro model called the human microbial crosstalk (HuMiX) gut-on-a-chip system. Here, we present the design, fabrication and integration of thin-film electrodes into the HuMiX platform to measure transepithelial electrical resistance (TEER) as a direct readout on barrier tightness in real-time. As various aspects of the HuMiX platform have already been set in their design, such as multiple compressible layers, uneven surfaces and nontransparent materials, a novel fabrication method was developed whereby thin-film metal electrodes were first deposited on flexible substrates and sequentially integrated with the HuMiX system via a transfer-tape approach. Moreover, to measure localized TEER along the cell culture chamber, we integrated multiple electrodes that were connected to an impedance analyzer via a multiplexer. We further developed a dynamic normalization method because the active measurement area depends on the measured TEER levels. The fabrication process and system setup can be applicable to other barrier-on-chip systems. As a proof-of-concept, we measured the barrier formation of a cancerous Caco-2 cell line in real-time, which was mapped at four spatially separated positions along the HuMiX culture area.

Protective Effects of Alginate and Chitosan Oligosaccharides against Clostridioides difficile Bacteria and Toxin

Clostridioides difficile infection is expected to become the most common healthcare-associated infection worldwide. C. difficile-induced pathogenicity is significantly attributed to its enterotoxin, TcdA, which primarily targets Rho-GTPases involved in regulating cytoskeletal and tight junction (TJ) dynamics, thus leading to cytoskeleton breakdown and ultimately increased intestinal permeability. This study investigated whether two non-digestible oligosaccharides (NDOs), alginate (AOS) and chitosan (COS) oligosaccharides, possess antipathogenic and barrier-protective properties against C. difficile bacteria and TcdA toxin, respectively. Both NDOs significantly reduced C. difficile growth, while cell cytotoxicity assays demonstrated that neither COS nor AOS significantly attenuated the TcdA-induced cell death 24 h post-exposure. The challenge of Caco-2 monolayers with increasing TcdA concentrations increased paracellular permeability, as measured by TEER and LY flux assays. In this experimental setup, COS completely abolished, and AOS mitigated, the deleterious effects of TcdA on the monolayer's integrity. These events were not accompanied by alterations in ZO-1 and occludin protein levels; however, immunofluorescence microscopy revealed that both AOS and COS prevented the TcdA-induced occludin mislocalization. Finally, both NDOs accelerated TJ reassembly upon a calcium-switch assay. Overall, this study established the antipathogenic and barrier-protective capacity of AOS and COS against C. difficile and its toxin, TcdA, while revealing their ability to promote TJ reassembly in Caco-2 cells.

Effects of Houpo Mahuang Decoction on serum metabolism and TRPV1/Ca2+/TJs in asthma

ETHNOPHARMACOLOGICAL RELEVANCE

Houpo Mahuang Decoction (HPMHD is one of the classic traditional Chinese prescriptions that has been used in the treatment of asthma. The therapeutic effects and mechanism of HPMHD in aggravated asthma remain to be explored, especially from the perspective of metabolomics and Transient Receptor Potential Vanilloid-1 (TRPV1)/Ca²⁺/Tight junction (TJ) regulation.

AIM OF THE STUDY

To investigate the therapeutic and metabolic regulatory effects and the underlying mechanism of HPMHD in asthmatic rats.

MATERIALS AND METHODS

The asthmatic rats were administered with the corresponding HPMHD (at dosages of 5.54, 11.07, 22.14 mg/kg). Then inflammatory cells in peripheral blood and bronchoalveolar lavage fluid (BALF) were counted, the levels of interleukin (IL)-4 and IL-13 in BALF were measured, and the changes in enhanced pause (Penh) and pathological damage of lung tissues were also detected to evaluate the protective effects of HPMHD. The serum metabolic profile of HPMHD in asthmatic rats was explored using Ultra-High-Performance Liquid Chromatography-mass spectrometer (UHPLC-MS), and the regulatory effects on TRPV1 and TJs of HPMHD in asthmatic rats were detected by Western blotting analysis. In vitro, 16HBE cells were stimulated with IL-4 plus SO₂ derivatives and then administered HPMHD. The intracellular Ca²⁺ regulated by TRPV1, and the expression levels of TRPV1 and TJ proteins (TJs) were then detected by calcium imaging and Western blotting. The effects were verified by inhibition of TRPV1 and in short hairpin RNA (shRNA)-mediated TRPV1 silencing cells.

RESULTS

HPMHD significantly attenuated the airway inflammation of asthmatic rats, and reduced the levels of inflammatory cells in peripheral blood and BALF as well as the levels of IL-4 plus IL-13 in BALF. In addition, the airway hyperresponsiveness and lung pathological damage were alleviated. Serum metabolomic analysis showed that 31 metabolites were differentially expressed among the normal saline-, model-, and HPMHD-treated rats. Pathway enrichment analysis showed that the metabolites were involved in 45 pathways, among which, TJs regulation-relevant pathway was associated with the Ca²⁺ concentration change mediated by the TRP Vanilloid channel. In vivo and in vitro experiments indicated that HPMHD reduced the concentration of intracellular Ca²⁺ via suppressing the expression and activation of TRPV1, increased the expression of ZO-1, Occludin, and Claudin-3, and protected the integrity of TJs.

CONCLUSION

The current study indicates that HPMHD alleviates rat asthma and participates in the regulation of serum metabolism. The anti-asthma effects of HPMHD might be related to the protection of TJs by inhibiting the intracellular Ca²⁺ concentration via TRPV1.

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.

Establishment of bovine 3D enteroid-derived 2D monolayers

Three-dimensional (3D) intestinal enteroids are powerful in vitro models for studying intestinal biology. However, due to their closed structure direct access to the apical surface is impeded, limiting high-throughput applications of exogenous compounds and pathogens. In this study, we describe a method for generating confluent 2D enteroids from single-cell suspensions of enzymatically-dissociated ileum-derived bovine 3D enteroids. Confluent monolayers were first achieved using IntestiCult media but to establish a defined, cost-effective culture media, we also developed a bovine enteroid monolayer (BEM) medium. The monolayers cultured in BEM media proliferated extensively and formed confluent cell layers on both Matrigel-coated plastic plates and transwell inserts by day 3 of culture. The 2D enteroids maintained the epithelial cell lineages found in 3D enteroids and ileum tissue. In addition, the monolayers formed a functional epithelial barrier based on the presence of the adherens and tight junction proteins, E-cadherin and ZO-1, and electrical resistance across the monolayer was measured from day 3 and maintained for up to 7 days in culture. The method described here will provide a useful model to study bovine epithelial cell biology with ease of access to the apical surface of epithelial cells and has potential to investigate host-pathogen interactions and screen bioactive compounds.

Novel chicken two-dimensional intestinal model comprising all key epithelial cell types and a mesenchymal sub-layer

The intestinal epithelium plays a variety of roles including providing an effective physical barrier and innate immune protection against infection. Two-dimensional models of the intestinal epithelium, 2D enteroids, are a valuable resource to investigate intestinal cell biology and innate immune functions and are suitable for high throughput studies of paracellular transport and epithelial integrity. We have developed a chicken 2D enteroid model that recapitulates all major differentiated cell lineages, including enterocytes, Paneth cells, Goblet cells, enteroendocrine cells and leukocytes, and self-organises into an epithelial and mesenchymal sub-layer. Functional studies demonstrated the 2D enteroids formed a tight cell layer with minimal paracellular flux and a robust epithelial integrity, which was maintained or rescued following damage. The 2D enteroids were also able to demonstrate appropriate innate immune responses following exposure to bacterial endotoxins, from Salmonella enterica serotype Typhimurium and Bacillus subtilis. Frozen 2D enteroids cells when thawed were comparable to freshly isolated cells. The chicken 2D enteroids provide a useful ex vivo model to study intestinal cell biology and innate immune function, and have potential uses in screening of nutritional supplements, pharmaceuticals, and bioactive compounds.