Evaluation of the Caco-2 monolayer as a model epithelium for iontophoretic transport

Horizontal and vertical microchamber platforms for evaluation of the paracellular permeability of an epithelial cell monolayer

Epithelial cells serve as a barrier by tightly adhering to each other and contribute to the homeostasis of living organisms by controlling substance permeation. Therefore, evaluation of the barrier function is important in pharmaceutical development processes. However, the widely used Transwell-based assays require the development of the defect-free epithelial cell monolayer above several tens of mm2, often resulting in low reproducibility and requiring a long incubation time. In addition, the culture surface of cells is far from the bottom of the well plate, making it difficult to observe the cell morphology using an optical microscope. Herein, we propose simple polydimethylsiloxane microfluidic devices for evaluating the barrier function of an epithelial monolayer using a microchamber array. After the formation of the epithelial monolayer over microchambers, the permeation of the marker molecules introduced above resulted in increased fluorescence intensity in microchambers, which was monitored using confocal laser scanning microscopy. We show that using this technique, alteration of the paracellular permeability induced by sodium caprate (C10) and cytochalasin-D, permeation enhancing factors, can be elucidated. Furthermore, by tilting the microchamber device 90 degrees, the vertical cell section and microchambers were imaged in the same focal plane, allowing for live visualization of the passage of fluorescent substances across the cell monolayer. This technique is expected to be useful for investigating the relationship between paracellular permeability and cell morphology, which is unattainable through conventional methods.

ADT-OH improves intestinal barrier function and remodels the gut microbiota in DSS-induced colitis

Owing to the increasing incidence and prevalence of inflammatory bowel disease (IBD) worldwide, effective and safe treatments for IBD are urgently needed. Hydrogen sulfide (H2S) is an endogenous gasotransmitter and plays an important role in inflammation. To date, H2S-releasing agents are viewed as potential anti-inflammatory drugs. The slow-releasing H2S donor 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADT-OH), known as a potent therapeutic with chemopreventive and cytoprotective properties, has received attention recently. Here, we reported its anti-inflammatory effects on dextran sodium sulfate (DSS)-induced acute (7 days) and chronic (30 days) colitis. We found that ADT-OH effectively reduced the DSS-colitis clinical score and reversed the inflammation-induced shortening of colon length. Moreover, ADT-OH reduced intestinal inflammation by suppressing the nuclear factor kappa-B pathway. In vivo and in vitro results showed that ADT-OH decreased intestinal permeability by increasing the expression of zonula occludens-1 and occludin and blocking increases in myosin II regulatory light chain phosphorylation and epithelial myosin light chain kinase protein expression levels. In addition, ADT-OH restored intestinal microbiota dysbiosis characterized by the significantly increased abundance of Muribaculaceae and Alistipes and markedly decreased abundance of Helicobacter, Mucispirillum, Parasutterella, and Desulfovibrio. Transplanting ADT-OH-modulated microbiota can alleviate DSS-induced colitis and negatively regulate the expression of local and systemic proinflammatory cytokines. Collectively, ADT-OH is safe without any short-term (5 days) or long-term (30 days) toxicological adverse effects and can be used as an alternative therapeutic agent for IBD treatment.

Adverse effects of linoleic acid: Influence of lipid oxidation on lymphatic transport of citrus flavonoid and enterocyte morphology

Lipids usually contain a large ratio of polyunsaturated fatty acids (PUFAs), which are highly susceptible to oxidation. Presence of oxidized lipids in foods may affect the bioavailability of lipophilic bioactive components after ingestion. In this study, the effect of oxidized and unoxidized linoleic acid (LA) on the transport of a highly lipophilic bioactive citrus flavonoid (5-hydroxy - 6, 7, 8, 4' tetramethoxylflavone or 5-DMT) was determined using a Caco-2 cell model. Results demonstrated that compared to free 5-DMT, unoxidized LA improved the trans-enterocyte absorption of 5-DMT by stimulating the production of lipid droplets and chylomicrons. Although the amount of 5-DMT transported across the enterocyte doubled by oxidized LA compared to free 5-DMT, it significantly induced reactive oxygen species (ROS), affected the function of tight junction and caused damages to the morphology of enterocyte monolayer. This study re-emphasized the importance of preventing lipid oxidation in foods.

Evaluation of Cellular Absorption and Metabolism of β-Carotene Loaded in Nanocarriers after In Vitro Digestion

Three protein emulsifiers encapsulating β-carotene (BC) with accompanying lipids into nanoemulsions (NEs) or without lipids into nanoparticles (NPs) were fabricated to study the effect of the type of interfacial protein on carrier design and the structure remodeling during digestion on the overall uptake and metabolism of BC in Caco-2 cells. BC-loaded micelles and micellar-like aggregates were collected after in vitro digestion and applied to Caco-2 cell monolayers. The digestion process significantly enhanced the cellular uptake of BC by 1.2-2.2 times and 4.1-8.2 times loaded in NEs and NPs, respectively. Whey protein isolate-based carriers improved the absorption but decreased the metabolism of BC to retinyl palmitate. The presence of lipids was found to improve metabolism and aid the transport of retinoids to the basolateral side of Caco-2 monolayers. Understanding the transportation behavior of the protein-based nanocarries after digestion may contribute to the design of biosafe carriers with higher bioavailability to deliver lipophilic nutrients.

Go with the flow: modeling unique biological flows in engineered in vitro platforms

Interest in recapitulating in vivo phenomena in vitro using organ-on-a-chip technology has grown rapidly and with it, attention to the types of fluid flow experienced in the body has followed suit. These platforms offer distinct advantages over in vivo models with regards to human relevance, cost, and control of inputs (e.g., controlled manipulation of biomechanical cues from fluid perfusion). Given the critical role biophysical forces play in several tissues and organs, it is therefore imperative that engineered in vitro platforms capture the complex, unique flow profiles experienced in the body that are intimately tied with organ function. In this review, we outline the complex and unique flow regimes experienced by three different organ systems: blood vasculature, lymphatic vasculature, and the intestinal system. We highlight current state-of-the-art platforms that strive to replicate physiological flows within engineered tissues while introducing potential limitations in current approaches.

Dually directional glycosylated phthalocyanines as extracellular red-emitting fluorescent probes

The development of new non-aggregated phthalocyanines bearing multivalent saccharide moieties on their macrocyclic rims is of great interest. Many characteristics, including water-solubility, non-toxicity and others, can be feasibly obtained by these amphiphiles which can be considered as a key solution for demonstrating highly efficient photoactive materials in water. Herein, a family of five newly prepared dually directional Zn(ii) containing phthalocyanines (PcG1-4) and azaphthalocyanine (AzaPcG1) glycoconjugates is described. The unique spatial arrangement of the glucoside units based on peripherally hexadeca-(PcG1) and nonperipherally octa-(PcG4) macrocycles provides a fully monomeric behaviour along with a high fluorescence (Φ_F∼ 0.21) in aqueous solution. These amphiphiles were characterized by low toxicity, and an extremely low cellular uptake was obtained due to the highly polar nature of the glucoside substituents. Accordingly, their potential as suitable photoactive chromophores for red-emitting extracellular fluorescent probes has been confirmed upon the evaluation of paracellular transport using a layer of MDCKII cells with the permeability coefficient fully comparable with an established evaluator of the integrity of the monolayer.

Rapid Prototyping of Multilayer Microphysiological Systems

Microfluidic organs-on-chips aim to realize more biorelevant in vitro experiments compared to traditional two-dimensional (2D) static cell culture. Often such devices are fabricated via poly(dimethylsiloxane) (PDMS) soft lithography, which offers benefits (e.g., high feature resolution) along with drawbacks (e.g., prototyping time/costs). Here, we report benchtop fabrication of multilayer, PDMS-free, thermoplastic organs-on-chips via laser cut and assembly with double-sided adhesives that overcome some limitations of traditional PDMS lithography. Cut and assembled chips are economical to prototype ($2 per chip), can be fabricated in parallel within hours, and are Luer compatible. Biocompatibility was demonstrated with epithelial line Caco-2 cells and primary human small intestinal organoids. Comparable to control static Transwell cultures, Caco-2 and organoids cultured on chips formed confluent monolayers expressing tight junctions with low permeability. Caco-2 cells-on-chip differentiated ∼4 times faster, including increased mucus, compared to controls. To demonstrate the robustness of cut and assemble, we fabricated a dual membrane, trilayer chip integrating 2D and 3D compartments with accessible apical and basolateral flow chambers. As proof of concept, we cocultured a human, differentiated monolayer and intact 3D organoids within multilayered contacting compartments. The epithelium exhibited 3D tissue structure and organoids expanded close to the adjacent monolayer, retaining proliferative stem cells over 10 days. Taken together, cut and assemble offers the capability to rapidly and economically manufacture microfluidic devices, thereby presenting a compelling fabrication technique for developing organs-on-chips of various geometries to study multicellular tissues.

Design of nanoemulsion-based delivery systems to enhance intestinal lymphatic transport of lipophilic food bioactives: Influence of oil type

The impact of nanoemulsions containing triglycerides with different fatty acid chain lengths on the bioavailability of a highly lipophilic bioactive: 5-demethylnobiletin (5-DN) was investigated. 5-DN was encapsulated in nanoemulsions fabricated using either medium-chain triglycerides (MCT) or long-chain triglycerides (LCT). They were then subjected to in vitro digestion, and the resulting mixed micelles was applied to a Caco-2 cell model. Higher 5-DN bioaccessibility was found for the MCT-nanoemulsion (13%) than for the LCT-nanoemulsion (7%). However, only 30% 5-DN in MCT crossed the Caco-2 monolayer and 50% was metabolized, while 60% 5-DN in LCT crossed the monolayer and only 10% was metabolized. More lipid droplets and chylomicrons were also formed for the LCT nanoemulsions, indicating greater 5-DN transported through lymph. Although MCT gave a higher 5-DN bioaccessibility, the final amount of 5-DN absorbed and transported to the lymph was inferior to that of the LCT formulation.

Intestinal iontophoresis from mucoadhesive patches: a strategy for oral delivery

Biologics have limited permeability across the intestine and are prone to degradation in the acidic-proteolytic milieu of the gastrointestinal tract, leading to poor oral bioavailability. Iontophoresis is a promising technology that can substantially improve transport of drugs across biological barriers and has been particularly explored for skin. In this study, we investigated whether iontophoresis across the intestine can be utilized to improve oral insulin transport. Application of electric current to intestinal cells resulted in opening of the tight junctions in vitro and a consequent about 3-fold improvement in paracellular transport of insulin. When evaluated in vivo using insulin-loaded mucoadhesive patches, iontophoresis produced profound hypoglycemia (63% blood glucose drop in 3 h) without damaging the intestinal tissue and the efficacy depended on insulin dose and current density. This study presents a proof of principle for intestinal iontophoresis as a novel method for oral protein delivery.

A Fixed Combination of Probiotics and Herbal Extracts Attenuates Intestinal Barrier Dysfunction from Inflammatory Stress in an In vitro Model Using Caco-2 Cells

BACKGROUND

Inflammatory Bowel Diseases (IBD), are considered a growing global disease, with about ten million people being affected worldwide. Maintenance of intestinal barrier integrity is crucial for preventing IBD onset and exacerbations. Some recent patents regarding oily formulations containing probiotics (WO2010122107A1 and WO2010103374A9) and the use of probiotics for gastrointestinal complaints (US20110110905A1 and US9057112B2) exist, or are pending application.

OBJECTIVE

In this work, we studied the effect of a fixed combination of registered Lactobacillus reuteri and Lactobacillus acidophilus strains and herbal extracts in an in vitro inflammation experimental model.

METHODS

Caco-2 cell monolayer was exposed to INF-γ+TNF-α or to LPS; Trans Epithelial Electrical Resistance (TEER) and paracellular permeability were investigated. ZO-1 and occludin Tight Junctions (TJs) were also investigated by mean of immunofluorescence.

RESULTS

Pre-treatment with the fixed combination of probiotics and herbal extracts prevented the inflammation-induced TEER decrease, paracellular permeability increase and TJs translocation.

CONCLUSIONS

In summary, the fixed combination of probiotics and herbal extracts investigated in this research was found to be an interesting candidate for targeting the re-establishment of intestinal barrier function in IBD conditions.

Microfluidic gut-on-a-chip with three-dimensional villi structure

Current in vitro gut models lack physiological relevance, and various approaches have been taken to improve current cell culture models. For example, mimicking the three-dimensional (3D) tissue structure or fluidic environment has been shown to improve the physiological function of gut cells. Here, we incorporated a collagen scaffold that mimics the human intestinal villi into a microfluidic device, thus providing cells with both 3D tissue structure and fluidic shear. We hypothesized that the combined effect of 3D structure and fluidic shear may provide cells with adequate stimulus to induce further differentiation and improve physiological relevance. The physiological function of our '3D gut chip' was assessed by measuring the absorptive permeability of the gut epithelium and activity of representative enzymes, as well as morphological evaluation. Our results suggest that the combination of fluidic stimulus and 3D structure induces further improvement in gut functions. Our work provides insight into the effect of different tissue environment on gut cells.

Electrostatic Self-Assembled Chitosan-Pectin Nano- and Microparticles for Insulin Delivery

A polyelectrolyte complex system of chitosan-pectin nano- and microparticles was developed to encapsulate the hormone insulin. The aim of this work was to obtain small particles for oral insulin delivery without chemical crosslinkers based on natural and biodegradable polysaccharides. The nano- and microparticles were developed using chitosans (with different degrees of acetylation: 15.0% and 28.8%) and pectin solutions at various charge ratios (n⁺/n^- given by the chitosan/pectin mass ratio) and total charge. Nano- and microparticles were characterized regarding particle size, zeta potential, production yield, encapsulation efficiency, stability in different media, transmission electron microscopy and cytotoxicity assays using Caco-2 cells. The insulin release was evaluated in vitro in simulated gastric and intestinal media. Small-sized particles (~240-~1900 nm) with a maximum production yield of ~34.0% were obtained. The highest encapsulation efficiency (~62.0%) of the system was observed at a charge ratio (n⁺/n^-) 5.00. The system was stable in various media, particularly in simulated gastric fluid (pH 1.2). Transmission electron microscopy (TEM) analysis showed spherical shape particles when insulin was added to the system. In simulated intestinal fluid (pH 6.8), controlled insulin release occurred over 2 h. In vitro tests indicated that the proposed system presents potential as a drug delivery for oral administration of bioactive peptides.

Polarized Airway Epithelial Models for Immunological Co-Culture Studies

Epithelial cells line all cavities and surfaces throughout the body and play a substantial role in maintaining tissue homeostasis. Asthma and other atopic diseases are increasing worldwide and allergic disorders are hypothesized to be a consequence of a combination of dysregulation of the epithelial response towards environmental antigens and genetic susceptibility, resulting in inflammation and T cell-derived immune responses. In vivo animal models have long been used to study immune homeostasis of the airways but are limited by species restriction and lack of exposure to a natural environment of both potential allergens and microflora. Limitations of these models prompt a need to develop new human cell-based in vitro models. A variety of co-culture systems for modelling the respiratory epithelium exist and are available to the scientific community. The models have become increasingly sophisticated and specific care needs to be taken with regard to cell types, culture medium and culture models, depending on the aim of the study. Although great strides have been made, there is still a need for further optimization, and optimally also for standardization, in order for in vitro co-culture models to become powerful tools in the discovery of key molecules dictating immunity and/or tolerance, and for understanding the complex interplay that takes place between mucosa, airway epithelium and resident or infiltrating immune cells. This review focuses on current knowledge and the advantages and limitations of the different cell types and culture methods used in co-culture models of the human airways.

Bacterial polysaccharide levan as stabilizing, non-toxic and functional coating material for microelement-nanoparticles

Levan, fructose-composed biopolymer of bacterial origin, has potential in biotechnology due to its prebiotic and immunostimulatory properties. In this study levan synthesized by levansucrase from Pseudomonas syringae was thoroughly characterized and used as multifunctional biocompatible coating material for microelement-nanoparticles (NPs) of selenium, iron and cobalt. Transmission electron microscopy (TEM), hydrodynamic size measurements (DLS) and X-ray photoelectron spectroscopy (XPS) showed the interaction of levan with NPs. Levan stabilized the dispersions of NPs, decreased their toxicity and had protective effect on human intestinal cells Caco-2. In addition, levan attached to cobalt NPs remained accessible as a substrate for the colon bacteria Bacteroides thetaiotaomicron. We suggest that the combination of levan and nutritionally important microelements in the form of NPs serves as a first step towards a novel "2 in 1" approach for food supplements to provide safe and efficient delivery of microelements for humans and support beneficial gut microbiota with nutritional oligosaccharides.

Alternative functional in vitro models of human intestinal epithelia

Physiologically relevant sources of absorptive intestinal epithelial cells are crucial for human drug transport studies. Human adenocarcinoma-derived intestinal cell lines, such as Caco-2, offer conveniences of easy culture maintenance and scalability, but do not fully recapitulate in vivo intestinal phenotypes. Additional sources of renewable physiologically relevant human intestinal cells would provide a much needed tool for drug discovery and intestinal physiology. We compared two alternative sources of human intestinal cells, commercially available primary human intestinal epithelial cells (hInEpCs) and induced pluripotent stem cell (iPSC)-derived intestinal cells to Caco-2, for use in in vitro transwell monolayer intestinal transport assays. To achieve this for iPSC-derived cells, intestinal organogenesis was adapted to transwell differentiation. Intestinal cells were assessed by marker expression through immunocytochemical and mRNA expression analyses, monolayer integrity through Transepithelial Electrical Resistance (TEER) measurements and molecule permeability, and functionality by taking advantage the well-characterized intestinal transport mechanisms. In most cases, marker expression for primary hInEpCs and iPSC-derived cells appeared to be as good as or better than Caco-2. Furthermore, transwell monolayers exhibited high TEER with low permeability. Primary hInEpCs showed molecule efflux indicative of P-glycoprotein (Pgp) transport. Primary hInEpCs and iPSC-derived cells also showed neonatal Fc receptor-dependent binding of immunoglobulin G variants. Primary hInEpCs and iPSC-derived intestinal cells exhibit expected marker expression and demonstrate basic functional monolayer formation, similar to or better than Caco-2. These cells could offer an alternative source of human intestinal cells for understanding normal intestinal epithelial physiology and drug transport.

Cytotoxicity of monodispersed chitosan nanoparticles against the Caco-2 cells

Published toxicology data on chitosan nanoparticles (NP) often lack direct correlation to the in situ size and surface characteristics of the nanoparticles, and the repeated NP assaults as experienced in chronic use. The aim of this paper was to breach these gaps. Chitosan nanoparticles synthesized by spinning disc processing were characterised for size and zeta potential in HBSS and EMEM at pHs 6.0 and 7.4. Cytotoxicity against the Caco-2 cells was evaluated by measuring the changes in intracellular mitochondrial dehydrogenase activity, TEER and sodium fluorescein transport data and cell morphology. Cellular uptake of NP was observed under the confocal microscope. Contrary to established norms, the collective data suggest that the in vitro cytotoxicity of NP against the Caco-2 cells was less influenced by positive surface charges than by the particle size. Particle size was in turn determined by the pH of the medium in which the NP was dispersed, with the mean size ranging from 25 to 333 nm. At exposure concentration of 0.1%, NP of 25 ± 7 nm (zeta potential 5.3 ± 2.8 mV) was internalised by the Caco-2 cells, and the particles were observed to inflict extensive damage to the intracellular organelles. Concurrently, the transport of materials along the paracellular pathway was significantly facilitated. The Caco-2 cells were, however, capable of recovering from such assaults 5 days following NP removal, although a repeat NP exposure was observed to produce similar effects to the 1st exposure, with the cells exhibiting comparable resiliency to the 2nd assault.

Comparison of 1-deoxynojirimycin and aqueous mulberry leaf extract with emphasis on postprandial hypoglycemic effects: in vivo and in vitro studies

Carbohydrate digestion by α-glucosidase and subsequent glucose uptake at the brush border are critical for postprandial blood glucose control. Any specific inhibitors are useful as hyperglycemia modulating agents. In this study, it was postulated that an array of active components in mulberry leaf extract (MLE) may provide higher potency in inhibiting intestinal glucose absorption compared to the single component 1-deoxynojirimycin (DNJ), which is recognized as a promising inhibitor of intestinal glucose absorption. Both MLE and DNJ were active in inhibiting α-glucosidase. However, in Caco-2 cells, only MLE showed significant inhibition of 2-deoxyglucose uptake, whereas DNJ was ineffective. For glucose loading, co-administration of MLE resulted in potent inhibitions of glucose responses compared to those by DNJ in Sprague Dawley (SD) rats, but this was not found for maltose loading. These novel findings add evidence that the unabsorbed phytochemicals in MLE compete with glucose for intestinal glucose transporters, but DNJ itself does not. We also evaluated the timing of MLE consumption. By administering MLE for 30 min before glucose loading, the incremental area under the curve (IAUC) was significantly lowered in the rats, as compared to a simultaneously administered group. Similarly, cellular glucose uptake was significantly reduced in Caco-2 cells following pretreatment.

Anti-proliferative effect of rhein, an anthraquinone isolated from Cassia species, on Caco-2 human adenocarcinoma cells

In recent years, the use of anthraquinone laxatives, in particular senna, has been associated with damage to the intestinal epithelial layer and an increased risk of developing colorectal cancer. In this study, we evaluated the cytotoxicity of rhein, the active metabolite of senna, on human colon adenocarcinoma cells (Caco-2) and its effect on cell proliferation. Cytotoxicity studies were performed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), neutral red (NR) and trans-epithelial electrical resistance (TEER) assays whereas ³H-thymidine incorporation and Western blot analysis were used to evaluate the effect of rhein on cell proliferation. Moreover, for genoprotection studies Comet assay and oxidative biomarkers measurement (malondialdehyde and reactive oxygen species) were used. Rhein (0.1–10 μg/ml) had no significant cytotoxic effect on proliferating and differentiated Caco-2 cells. Rhein (0.1 and 1 μg/ml) significantly reduced cell proliferation as well as mitogen-activated protein (MAP) kinase activation; by contrast, at high concentration (10 μg/ml) rhein significantly increased cell proliferation and extracellular-signal-related kinase (ERK) phosphorylation. Moreover, rhein (0.1–10 μg/ml): (i) did not adversely affect the integrity of tight junctions and hence epithelial barrier function; (ii) did not induce DNA damage, rather it was able to reduce H₂O₂-induced DNA damage and (iii) significantly inhibited the increase in malondialdehyde and reactive oxygen species (ROS) levels induced by H₂O₂/Fe²⁺. Rhein was devoid of cytotoxic and genotoxic effects in colon adenocarcinoma cells. Moreover, at concentrations present in the colon after a human therapeutic dosage of senna, rhein inhibited cell proliferation via a mechanism that seems to involve directly the MAP kinase pathway. Finally, rhein prevents the DNA damage probably via an anti-oxidant mechanism.

Dexamethasone-pDMAEMA polymeric conjugates reduce inflammatory biomarkers in human intestinal epithelial monolayers

The mucoadhesive polymer, poly(dimethylamino)ethyl methacrylate, (pDMAEMA), was synthesised by living radical polymerisation and subsequently conjugated by quaternisation reaction to a functionalised anti-inflammatory corticosteroid dexamethasone, to separately yield two conjugates with either 9:1 or 18:1 molar ratios of dexamethasone:polymer respectively. The hypothesis was to test whether the active agent maintained in vitro bioactivity when exposed to the apical side of human intestinal epithelial monolayers, Caco-2 and mucus-covered HT29-MTX-E12 (E12). HPLC analysis indicated high conjugate purity. Similar to pDMAEMA, fluorescently-labelled dexamethasone-pDMAEMA conjugates were bioadhesive to Caco-2 and mucoadhesive to E12. Apical addition of conjugates suppressed mRNA expression of the inflammatory markers, NURR1 and ICAM-1 in E12 following stimulation by PGE(2) and TNF-alpha, respectively. Conjugates also suppressed TNF-alpha stimulated cytokine secretion to the basolateral side of Caco-2 monolayers. Measurement of dexamethasone permeability from conjugates across monolayers suggested that conjugation reduced permeability compared to free dexamethasone. LDH assay indicated that conjugates were not cytotoxic to monolayers. Anti-inflammatory agents can therefore be successfully conjugated to polymers and they retain adhesion and bioactivity and have potential to be formulated for topical administration.

In vitro Interactions Between the Oral Absorption Promoter, Sodium Caprate (C10) and S. typhimurium in Rat Intestinal Ileal Mucosae

PURPOSE

The medium chain fatty acid, sodium caprate (C(10)), is a promising oral drug delivery agent that may promote permeability of peptides through increasing paracellular permeability of the intestinal epithelium. One safety concern is that it may permit co-absorption of by-stander agents including pathogens. The purpose of this in vitro study was to examine the effects of C(10) on rat intestinal ileal mucosae in the presence of co-administered Salmonella typhimurium in a low volume vertical Ussing chamber.

METHODS

C(10) or S. typhimurium was added to rat ileal mucosae mounted in chambers and the flux of the paracellular flux of [(14)C]-mannitol examined. S. typhimurium adherence and uptake by ileal mucosae was also examined by counting. Bacterial growth curves were assessed in the presence of C(10). Minimum inhibitory- and bacteriocidal concentrations of C(10) were determined against a range of bacteria.

RESULTS

Apical addition of either C(10) or S. typhimurium to rat ileal mucosae mounted in modified diffusion chambers significantly increased the flux of [(14)C]-mannitol in a concentration-dependent fashion. Co-exposure with increasing concentrations of C(10) attenuated the Salmonella-induced increase in mannitol flux. Histological evaluation revealed that C(10) inhibited both adhesion and invasion of S. typhimurium to intestinal mucosae. Short term bacterial growth studies in the presence of C(10) showed evidence of concentration-dependent inhibition. C(10) was bacteriocidal in mM concentrations against S. typhimurium and selected gram positive and negative bacteria.

CONCLUSIONS

C(10) does not promote the permeation of a common bacterium across isolated intestinal tissue upon acute co-exposure. It prevents S. typhimurium attachment to epithelia and impedes growth of a range of different bacterial strains.

Interleukin-6 induces keratin expression in intestinal epithelial cells: potential role of keratin-8 in interleukin-6-induced barrier function alterations

Keratin 8 (K8) and keratin-18 (K18) are the major intermediate filament proteins in the intestinal epithelia. The regulation and function of keratin in the intestinal epithelia is largely unknown. In this study we addressed the role and regulation of K8 and K18 expression by interleukin 6 (IL-6). Caco2-BBE cell line and IL-6 null mice were used to study the effect of IL-6 on keratin expression. Keratin expression was studied by Northern blot, Western blot, and confocal microscopy. Paracellular permeability was assessed by apical-to-basal transport of a fluorescein isothiocyanate dextran probe (FD-4). K8 was silenced using the small interfering RNA approach. IL-6 significantly up-regulated mRNA and protein levels of K8 and K18. Confocal microscopy showed a reticular pattern of intracellular keratin localized to the subapical region after IL-6 treatment. IL-6 also induced serine phosphorylation of K8. IL-6 decreased paracellular flux of FD-4 compared with vehicle-treated monolayers. K8 silencing abolished the decrease in paracellular permeability induced by IL-6. Administration of dextran sodium sulfate (DSS) significantly increased intestinal permeability in IL-6-/- mice compared with wild type mice given DSS. Collectively, our data demonstrate that IL-6 regulates the colonic expression of K8 and K18, and K8/K18 mediates barrier protection by IL-6 under conditions where intestinal barrier is compromised. Thus, our data uncover a novel function of these abundant cytoskeletal proteins, which may have implications in intestinal disorders such as inflammatory bowel disease wherein barrier dysfunction underlies the inflammatory response.

Human respiratory epithelial cell culture for drug delivery applications

Recent developments in delivering drugs to the lung are driving the need for in vitro methods to evaluate the fate of inhaled medicines. Constraints on experimentation using animals have promoted the use of human respiratory epithelial cell cultures to model the absorption barrier of the lung; with two airway cell lines, 16HBE14o- and Calu-3, and primary cultured human alveolar type I-like cells (hAEpC) gaining prominence. These in vitro models develop permeability properties which are comparable to those reported for native lung epithelia. This is in contrast to the high permeability of the A549 human alveolar cell line, which is unsuitable for use in drug permeability experiments. Tabulation of apparent permeability coefficients (Papp) of compounds measured in 'absorptive' and 'secretory' directions reveals that fewer compounds (< 15) have been evaluated in 16HBE14o- cells and hAEpC compared to Calu-3 cells (> 50). Vectorial (asymmetric) transport of compounds is reported in the three cell types with P-glycoprotein, the most studied transport mechanism, being reported in all. Progress is being made towards in vitro-in vivo-correlation for pulmonary absorption and in the use of cultured respiratory cells to evaluate drug metabolism, toxicity and targeting strategies. In summary, methods for the culture of human respiratory epithelial cell layers have been established and data regarding their permeability characteristics and suitability to model the lung is becoming available. Discerning the circumstances under which the use of human respiratory cell models will be essential, or offers advantages over non-organ, non-species specific cell models, is the next challenge.

In vitro and ex vivo intestinal tissue models to measure mucoadhesion of poly (methacrylate) and N-trimethylated chitosan polymers

PURPOSE

The adhesion of a range of polymers based on poly(2-(dimethylamino-ethyl) methacrylate (pDMAEMA) was assessed using human mucus-secreting and non mucus-secreting intestinal cell monolayers, HT29-MTX-E12 (E12) and HT29 monolayers, as well as excised non-everted intestinal sacs from rats. Differentiation of mucoadhesion from bioadhesion was achieved by pre-treatment with the mucolytic agent, N-acetyl cysteine (NAC). Adherence of pDMAEMA polymers was compared to that obtained with the mucoadhesive, N-trimethylated chitosan (TMC).

METHODS

The quantity of adherent coumarin 343-conjugated polymers to HT29, E12, and intestinal sacs was measured by fluorescence. Confocal laser scanning microscopy (CLSM), light microscopy, and fluorescent microscopy were used to provide direct evidence. Measurements of transepithelial electrical resistance (TEER), permeability to FITC-dextran 4000 (FD-4), and the release of lactate dehydrogenase (LDH) were used to assess potential cytotoxicity of polymers.

RESULTS

Adherence of unquaternized and of 10%, 24%, and 32% methyl iodide-quaternized pDMAEMA polymers was measured in E12, HT29, and sacs. All pDMAEMA polymers showed significantly higher levels of adhesion to mucus (mucoadhesion) than to epithelium (bioadhesion). Colocalization of pDMAEMA with mucus was confirmed in E12 by microscopy. TMC showed equally high levels of mucoadhesion as unquaternized and 24% quaternized pDMAEMA, but displayed higher levels of bioadhesion. pDMAEMA-based polymers demonstrated lower levels of adherence to E12 and rat sacs in the presence of NAC, whereas adherence of TMC was unchanged. pDMAEMA significantly decreased the permeability of FD-4 across E12 monolayers and sacs and was less cytotoxic in E12 than in HT29. In contrast, TMC increased the permeability of FD-4 across E12 and sacs and was less cytotoxic in E12 than in HT29.

CONCLUSIONS

Human mucus-producing E12 monolayers can be used to assess polymer mucoadhesion and give similar data to isolated rat intestinal sacs. pDMAEMA displayed similar levels of mucoadhesion and lower levels of bioadhesion than a chitosan derivative and it was not cytotoxic. pDMAEMA decreased FD-4 flux in the presence of mucus, whereas TMC increased it. The combination of mucus and methacrylate polymers appears to increase barrier function of the apical membrane.

Increased permeability of intestinal epithelial monolayers mediated by electroporation

This study assessed whether electroporation enhances transport across intact intestinal epithelial monolayers that mimic the intestinal epithelium. Confluent Caco-2 monolayers were exposed to electroporation pulses and then monitored over time for transepithelial transport of calcein, a small fluorescent tracer, or fluorescein-labeled bovine serum albumin, a large protein. Cumulative transport of both molecules across the monolayers increased significantly (up to 34-fold) after electroporation and depended on electroporation voltage and pulse length and on molecular size. Increased transport was accompanied by a decrease in the transepithelial electrical resistance of the monolayers. Further analysis of these results suggests that the increase in transport observed after electroporation is due, at least in part, to the killing of a small fraction of cells, which increased transport across "leaky" dead cells that remained adherent and increased transport through small, temporary holes left by dead cells that detached, but appeared to reseal within minutes by monolayer restitution. These findings could form the basis for the development of electroporation as a clinical tool to increase intestinal permeability and, thereby, increase the absorption of poorly absorbed drugs.

Electroporation-mediated delivery of molecules to model intestinal epithelia

This study was conducted to determine if electroporation can deliver membrane-impermeant molecules intracellularly to intact, physiologically competent monolayers that mimic the intestinal epithelium. In addition, the long-term effects of electroporation on these monolayers were studied to determine the kinetics with which monolayers recover barrier function. Caco-2 and T84 cells were electroporated as monolayers using calcein and fluorescein-labeled bovine serum albumin as marker molecules for measuring delivery into cells. Confocal microscopy and flow cytometry were used, respectively, to visualize and quantify uptake of these molecules. Transepithelial resistance was used as a measure of physiologic barrier function. We found that intracellular uptake of calcein and bovine serum albumin occurred uniformly throughout both types of model epithelia and increased as a function of voltage, pulse length, and pulse number. There was no significant difference in uptake resulting from single and multiple pulses of the same total exposure time. We also observed that monolayers exposed to electroporation that induced uptake of up to 10(6) molecules/cell were able to recover normal barrier function within one day. These findings suggest that electroporation may be useful for intracellular delivery into monolayers to study epithelial biology and, possibly, for drug delivery to intestinal epithelium.

Shiga toxin translocation across intestinal epithelial cells is enhanced by neutrophil transmigration

Shiga toxin-producing E. coli (STEC) is a food-borne pathogen that causes serious illness, including hemolytic-uremic syndrome (HUS). STEC colonizes the lower intestine and produces Shiga toxins (Stxs). Stxs appear to translocate across intestinal epithelia and affect sensitive endothelial cell beds at various sites. We have previously shown that Stxs cross polarized intestinal epithelial cells (IECs) via a transcellular route and remain biologically active. Since acute inflammatory infiltration of the gut and fecal leukocytes is seen in many STEC-infected patients and since polymorphonuclear leukocyte (PMN) transmigration across polarized IECs diminishes the IEC barrier function in vitro, we hypothesized that PMN transmigration may enhance Stx movement across IECs. We found that basolateral-to-apical transmigration of neutrophils significantly increased the movement of Stx1 and Stx2 across polarized T84 IECs in the opposite direction. The amount of Stx crossing the T84 barrier was proportional to the degree of neutrophil transmigration, and the increase in Stx translocation appears to be due to increases in paracellular permeability caused by migrating PMNs. STEC clinical isolates applied apically induced PMN transmigration across and interleukin-8 (IL-8) secretion from T84 cells. Of the 10 STEC strains tested, three STEC strains lacking eae and espB (eae- and espB-negative STEC strains) induced significantly more neutrophil transmigration and significantly greater IL-8 secretion than eae- and espB-positive STEC or enteropathogenic E. coli. This study suggests that STEC interaction with intestinal epithelia induces neutrophil recruitment to the intestinal lumen, resulting in neutrophil extravasation across IECs, and that during this process Stxs may pass in greater amounts into underlying tissues, thereby increasing the risk of HUS.