Paracellular barrier and junctional protein distribution depend on basolateral extracellular Ca2+ in cultured epithelia

Storming the gate: New approaches for targeting the dynamic tight junction for improved drug delivery

As biologics used in the clinic outpace the number of new small molecule drugs, an important challenge for their efficacy and widespread use has emerged, namely tissue penetrance. Macromolecular drugs - bulky, high-molecular weight, hydrophilic agents - exhibit low permeability across biological barriers. Epithelial and endothelial layers, for example within the gastrointestinal tract or at the blood-brain barrier, present the most significant obstacle to drug transport. Within epithelium, two subcellular structures are responsible for limiting absorption: cell membranes and intercellular tight junctions. Previously considered impenetrable to macromolecular drugs, tight junctions control paracellular flux and dictate drug transport between cells. Recent work, however, has shown tight junctions to be dynamic, anisotropic structures that can be targeted for delivery. This review aims to summarize new approaches for targeting tight junctions, both directly and indirectly, and to highlight how manipulation of tight junction interactions may help usher in a new era of precision drug delivery.

The Effects of a High-Fat Diet on Inflammatory Bowel Disease

The interactions among diet, intestinal immunity, and microbiota are complex and play contradictory roles in inflammatory bowel disease (IBD). An increasing number of studies has shed light on this field. The intestinal immune balance is disrupted by a high-fat diet (HFD) in several ways, such as impairing the intestinal barrier, influencing immune cells, and altering the gut microbiota. In contrast, a rational diet is thought to maintain intestinal immunity by regulating gut microbiota. In this review, we emphasize the crucial contributions made by an HFD to the gut immune system and microbiota.

Nanomaterial-mediated photoporation for intracellular delivery

Translocation of extrinsic molecules into living cells is becoming increasingly crucial in biological studies ranging from cell engineering to biomedical applications. The concerns regarding biosafety and immunogenicity for conventional vectors and physical methods yet challenge effective intracellular delivery. Here, we begin with an overview of approaches for trans-membrane delivery up to now. These methods are featured with a relatively mature application but usually encounter low cell survival. Our review then proposes an advanced application for nanomaterial-sensitized photoporation triggered with a laser. We cover the mechanisms, procedures, and outcomes of photoporation-induced intracellular delivery with a highlight on its versatility to different living cells. We hope the review discussed here encourages researchers to further improvement and applications for photoporation-induced intracellular delivery. STATEMENT OF SIGNIFICANCE.

Intestinal absorption mechanism of rotundic acid: Involvement of P-gp and OATP2B1

ETHNOPHARMACOLOGICAL RELEVANCE

Ilicis Rotundae Cortex (IRC), the dried barks of Ilex rotunda Thunb. (Aquifoliaceae), has been used for the prevention or treatment of colds, tonsillitis, dysentery, and gastrointestinal diseases in folk medicine due to its antibacterial and anti-inflammatory effects. However, there is no report about the intestinal absorption of major compounds that support traditional usage.

AIM OF STUDY

Considering the potential of rotundic acid (RA) - major biologically active pentacyclic triterpenes found in the IRC, this study was purposed to uncover the oral absorption mechanism of RA using in situ single-pass intestinal perfusion (SPIP) model, in vitro cell models (Caco-2, MDCKII-WT, MDCKII-MDR1, MDCKII-BCRP, and HEK293-OATP2B1 cells) and in vivo pharmacokinetics studies in rats.

MATERIALS AND METHODS

The molecular properties (solubility, lipophilicity, and chemical stability) and the effects of principal parameters (time, compound concentrations, pH, paracellular pathway, and the different intestinal segments) were analyzed by liquid chromatography-tandem mass spectrometry. The susceptibility of RA to various inhibitors, such as P-gp inhibitor verapamil, BCRP inhibitor Ko143, OATP 2B1 inhibitor rifampicin, and absorption enhancer EGTA were assessed.

RESULTS

RA was a compound with low water solubility (12.89 μg/mL) and strong lipophilicity (LogP = 4.1). RA was considered stable in all media during the SPIP and transport studies. The SPIP and cell experiments showed RA was moderate absorbed in the intestines and exhibited time, concentration, pH, and segment-dependent permeability. In addition, results from the cell model, in situ SPIP model as well as the in vivo pharmacokinetics studies consistently showed that verapamil, rifampicin, and EGTA might have significant effect on the intestinal absorption of RA.

CONCLUSION

The mechanisms of intestinal absorption of RA might involve multiple transport pathways, including passive diffusion, the participation of efflux (i.e., P-gp) and influx (i.e., OATP2B1) transporters, and paracellular pathways.

Characteristics of Passive Solute Transport across Primary Rat Alveolar Epithelial Cell Monolayers

Primary rat alveolar epithelial cell monolayers (RAECM) were grown without (type I cell-like phenotype, RAECM-I) or with (type II cell-like phenotype, RAECM-II) keratinocyte growth factor to assess passive transport of 11 hydrophilic solutes. We estimated apparent permeability (Papp) in the absence/presence of calcium chelator EGTA to determine the effects of perturbing tight junctions on "equivalent" pores. Papp across RAECM-I and -II in the absence of EGTA are similar and decrease as solute size increases. We modeled Papp of the hydrophilic solutes across RAECM-I/-II as taking place via heterogeneous populations of equivalent pores comprised of small (0.41/0.32 nm radius) and large (9.88/11.56 nm radius) pores, respectively. Total equivalent pore area is dominated by small equivalent pores (99.92-99.97%). The number of small and large equivalent pores in RAECM-I was 8.55 and 1.29 times greater, respectively, than those in RAECM-II. With EGTA, the large pore radius in RAECM-I/-II increased by 1.58/4.34 times and the small equivalent pore radius increased by 1.84/1.90 times, respectively. These results indicate that passive diffusion of hydrophilic solutes across an alveolar epithelium occurs via small and large equivalent pores, reflecting interactions of transmembrane proteins expressed in intercellular tight junctions of alveolar epithelial cells.

An Intratumor Pharmacokinetic/Pharmacodynamic Model for the Hypoxia-Activated Prodrug Evofosfamide (TH-302): Monotherapy Activity is Not Dependent on a Bystander Effect

Tumor hypoxia contributes to resistance to anticancer therapies. Hypoxia-activated prodrugs (HAPs) selectively target hypoxic cells and their activity can extend to well-oxygenated areas of tumors via diffusion of active metabolites. This type of bystander effect has been suggested to be responsible for the single agent activity of the clinical-stage HAP evofosfamide (TH-302) but direct evidence is lacking. To dissect the contribution of bystander effects to TH-302 activity, we implemented a Green's function pharmacokinetic (PK) model to simulate the spatial distribution of O₂, TH-302 and its cytotoxic metabolites, bromo-isophosphoramide mustard (Br-IPM) and its dichloro derivative isophosphoramide mustard (IPM), in two digitized tumor microvascular networks. The model was parameterized from literature and experimentally, including measurement of diffusion coefficients of TH-302 and its metabolites in multicellular layer cultures. The latter studies demonstrate that Br-IPM and IPM cannot diffuse significantly from the cells in which they are generated, although evidence was obtained for diffusion of the hydroxylamine metabolite of TH-302. The spatially resolved PK model was linked to a pharmacodynamic (PD) model that describes cell killing probability at each point in the tumor microregion as a function of Br-IPM and IPM exposure. The resulting PK/PD model accurately predicted previously reported monotherapy activity of TH-302 in H460 tumors, without invoking a bystander effect, demonstrating that the notable single agent activity of TH-302 in tumors can be accounted for by significant bioreductive activation of TH-302 even in oxic regions, driven by the high plasma concentrations achievable with this well-tolerated prodrug.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

Intestinal Cell Tight Junctions Limit Invasion of Candida albicans through Active Penetration and Endocytosis in the Early Stages of the Interaction of the Fungus with the Intestinal Barrier

C. albicans is a commensal yeast of the mucous membranes in healthy humans that can also cause disseminated candidiasis, mainly originating from the digestive tract, in vulnerable patients. It is necessary to understand the cellular and molecular mechanisms of the interaction of C. albicans with enterocytes to better understand the basis of commensalism and pathogenicity of the yeast and to improve the management of disseminated candidiasis. In this study, we investigated the kinetics of tight junction (TJ) formation in parallel with the invasion of C. albicans into the Caco-2 intestinal cell line. Using invasiveness assays on Caco-2 cells displaying pharmacologically altered TJ (i.e. differentiated epithelial cells treated with EGTA or patulin), we were able to demonstrate that TJ protect enterocytes against invasion of C. albicans. Moreover, treatment with a pharmacological inhibitor of endocytosis decreased invasion of the fungus into Caco-2 cells displaying altered TJ, suggesting that facilitating access of the yeast to the basolateral side of intestinal cells promotes endocytosis of C. albicans in its hyphal form. These data were supported by SEM observations of differentiated Caco-2 cells displaying altered TJ, which highlighted membrane protrusions engulfing C. albicans hyphae. We furthermore demonstrated that Als3, a hypha-specific C. albicans invasin, facilitates internalization of the fungus by active penetration and induced endocytosis by differentiated Caco-2 cells displaying altered TJ. However, our observations failed to demonstrate binding of Als3 to E-cadherin as the trigger mechanism of endocytosis of C. albicans into differentiated Caco-2 cells displaying altered TJ.

Listeriolysin O Affects the Permeability of Caco-2 Monolayer in a Pore-Dependent and Ca2+-Independent Manner

Listeria monocytogenes is a food and soil-borne pathogen that secretes a pore-forming toxin listeriolysin O (LLO) as its major virulence factor. We tested the effects of LLO on an intestinal epithelial cell line Caco-2 and compared them to an unrelated pore-forming toxin equinatoxin II (EqtII). Results showed that apical application of both toxins causes a significant drop in transepithelial electrical resistance (TEER), with higher LLO concentrations or prolonged exposure time needed to achieve the same magnitude of response than with EqtII. The drop in TEER was due to pore formation and coincided with rearrangement of claudin-1 within tight junctions and associated actin cytoskeleton; however, no significant increase in permeability to fluorescein or 3 kDa FITC-dextran was observed. Influx of calcium after pore formation affected the magnitude of the drop in TEER. Both toxins exhibit similar effects on epithelium morphology and physiology. Importantly, LLO action upon the membrane is much slower and results in compromised epithelium on a longer time scale at lower concentrations than EqtII. This could favor listerial invasion in hosts resistant to E-cadherin related infection.

Sensing of EGTA Mediated Barrier Tissue Disruption with an Organic Transistor

Barrier tissue protects the body against external factors by restricting the passage of molecules. The gastrointestinal epithelium is an example of barrier tissue with the primary purpose of allowing the passage of ions and nutrients, while restricting the passage of pathogens and toxins. It is well known that the loss of barrier function can be instigated by a decrease in extracellular calcium levels, leading to changes in protein conformation and an increase in paracellular transport. In this study, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra acetic acid (EGTA), a calcium chelator, was used to disrupt the gastrointestinal epithelial barrier. The effect of EGTA on barrier tissue was monitored by a novel label-free method based on an organic electrochemical transistor (OECT) integrated with living cells and validated against conventional methods for measuring barrier tissue integrity. We demonstrate that the OECT can detect breaches in barrier tissue upon exposure to EGTA with the same sensitivity as existing methods but with increased temporal resolution. Due to the potential of low cost processing techniques and the flexibility in design associated with organic electronics, the OECT has great potential for high-throughput, disposable sensing and diagnostics.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

EB1 levels are elevated in ascorbic Acid (AA)-stimulated osteoblasts and mediate cell-cell adhesion-induced osteoblast differentiation

Osteoblasts are differentiated mesenchymal cells that function as the major bone-producing cells of the body. Differentiation cues including ascorbic acid (AA) stimulation provoke intracellular changes in osteoblasts leading to the synthesis of the organic portion of the bone, which includes collagen type I α1, proteoglycans, and matrix proteins, such as osteocalcin. During our microarray analysis of AA-stimulated osteoblasts, we observed a significant up-regulation of the microtubule (MT) plus-end binding protein, EB1, compared with undifferentiated osteoblasts. EB1 knockdown significantly impaired AA-induced osteoblast differentiation, as detected by reduced expression of osteoblast differentiation marker genes. Intracellular examination of AA-stimulated osteoblasts treated with EB1 siRNA revealed a reduction in MT stability with a concomitant loss of β-catenin distribution at the cell cortex and within the nucleus. Diminished β-catenin levels in EB1 siRNA-treated osteoblasts paralleled an increase in phospho-β-catenin and active glycogen synthase kinase 3β, a kinase known to target β-catenin to the proteasome. EB1 siRNA treatment also reduced the expression of the β-catenin gene targets, cyclin D1 and Runx2. Live immunofluorescent imaging of differentiated osteoblasts revealed a cortical association of EB1-mcherry with β-catenin-GFP. Immunoprecipitation analysis confirmed an interaction between EB1 and β-catenin. We also determined that cell-cell contacts and cortically associated EB1/β-catenin interactions are necessary for osteoblast differentiation. Finally, using functional blocking antibodies, we identified E-cadherin as a major contributor to the cell-cell contact-induced osteoblast differentiation.

Nanoparticle translocation across mouse alveolar epithelial cell monolayers: species-specific mechanisms

Studies of polystyrene nanoparticle (PNP) trafficking across mouse alveolar epithelial cell monolayers (MAECM) show apical-to-basolateral flux of 20 and 120nm amidine-modified PNP is ~65 times faster than that of 20 and 100nm carboxylate-modified PNP, respectively. Calcium chelation with EGTA has little effect on amidine-modified PNP flux, but increases carboxylate-modified PNP flux ~50-fold. PNP flux is unaffected by methyl-β-cyclodextrin, while ~70% decrease in amidine- (but not carboxylate-) modified PNP flux occurs across chlorpromazine- or dynasore-treated MAECM. Confocal microscopy reveals intracellular amidine- and carboxylate-modified PNP and association of amidine- (but not carboxylate-) modified PNP with clathrin heavy chain. These data indicate (1) amidine-modified PNP translocate across MAECM primarily via clathrin-mediated endocytosis and (2) physicochemical properties (e.g., surface charge) determine PNP interactions with mouse alveolar epithelium. Uptake/trafficking of nanoparticles into/across epithelial barriers is dependent on both nanoparticle physicochemical properties and (based on comparison with our prior results) specific epithelial cell type.

FROM THE CLINICAL EDITOR

In this study of polystyrene nanoparticle trafficking across mouse alveolar epithelial cell monolayers, the authors determined that uptake/trafficking of nanoparticles into/across epithelial barriers is dependent on both nanoparticle physicochemical properties and the specific type of epithelial cells.

Oral delivery of therapeutic protein/peptide for diabetes--future perspectives

Diabetes is a metabolic disease and is a major cause of mortality and morbidity in epidemic proportions. A type I diabetic patient is dependent on daily injections of insulin, for survival and also to maintain a normal life, which is uncomfortable, painful and also has deleterious effects. Extensive efforts are being made worldwide for developing noninvasive drug delivery systems, especially via oral route. Oral route is the most widely accepted means of administration. However it is not feasible for direct delivery of peptide and protein drugs. To overcome the gastro-intestinal barriers various types of formulations such as polymeric micro/nanoparticles, liposomes, etc. are investigated. In the recent years lot of advances have taken place in developing and understanding the oral peptide delivery systems. Simultaneously, the development and usage of other peptides having anti-diabetic potentials are also considered for diabetes therapy. In this review we are focusing on the advances reported during the past decade in the field of oral insulin delivery along with the possibility of other peptidic incretin hormones such as GLP-1, exendin-4, for diabetes therapy.

Translocation of PEGylated quantum dots across rat alveolar epithelial cell monolayers

BACKGROUND

In this study, primary rat alveolar epithelial cell monolayers (RAECM) were used to investigate transalveolar epithelial quantum dot trafficking rates and underlying transport mechanisms.

METHODS

Trafficking rates of quantum dots (PEGylated CdSe/ZnS, core size 5.3 nm, hydrodynamic size 25 nm) in the apical-to-basolateral direction across RAECM were determined. Changes in bioelectric properties (ie, transmonolayer resistance and equivalent active ion transport rate) of RAECM in the presence or absence of quantum dots were measured. Involvement of endocytic pathways in quantum dot trafficking across RAECM was assessed using specific inhibitors (eg, methyl-β-cyclodextrin, chlorpromazine, and dynasore for caveolin-, clathrin-, and dynamin-mediated endocytosis, respectively). The effects of lowering tight junctional resistance on quantum dot trafficking were determined by depleting Ca(2+) in apical and basolateral bathing fluids of RAECM using 2 mM EGTA. Effects of temperature on quantum dot trafficking were studied by lowering temperature from 37°C to 4°C.

RESULTS

Apical exposure of RAECM to quantum dots did not elicit changes in transmonolayer resistance or ion transport rate for up to 24 hours; quantum dot trafficking rates were not surface charge-dependent; methyl-β-cyclodextrin, chlorpromazine, and dynasore did not decrease quantum dot trafficking rates; lowering of temperature decreased transmonolayer resistance by approximately 90% with a concomitant increase in quantum dot trafficking by about 80%; and 24 hours of treatment of RAECM with EGTA decreased transmonolayer resistance by about 95%, with increased quantum dot trafficking of up to approximately 130%.

CONCLUSION

These data indicate that quantum dots do not injure RAECM and that quantum dot trafficking does not appear to take place via endocytic pathways involving caveolin, clathrin, or dynamin. We conclude that quantum dot translocation across RAECM takes place via both transcellular and paracellular pathways and, based on comparison with our prior studies, interactions of nanoparticles with RAECM are strongly dependent on nanoparticle composition and surface properties.

Micropatterned mammalian cells exhibit phenotype-specific left-right asymmetry

Left-right (LR) asymmetry (handedness, chirality) is a well-conserved biological property of critical importance to normal development. Changes in orientation of the LR axis due to genetic or environmental factors can lead to malformations and disease. While the LR asymmetry of organs and whole organisms has been extensively studied, little is known about the LR asymmetry at cellular and multicellular levels. Here we show that the cultivation of cell populations on micropatterns with defined boundaries reveals intrinsic cell chirality that can be readily determined by image analysis of cell alignment and directional motion. By patterning 11 different types of cells on ring-shaped micropatterns of various sizes, we found that each cell type exhibited definite LR asymmetry (p value down to 10(-185)) that was different between normal and cancer cells of the same type, and not dependent on surface chemistry, protein coating, or the orientation of the gravitational field. Interestingly, drugs interfering with actin but not microtubule function reversed the LR asymmetry in some cell types. Our results show that micropatterned cell populations exhibit phenotype-specific LR asymmetry that is dependent on the functionality of the actin cytoskeleton. We propose that micropatterning could potentially be used as an effective in vitro tool to study the initiation of LR asymmetry in cell populations, to diagnose disease, and to study factors involved with birth defects in laterality.

Polystyrene nanoparticle trafficking across MDCK-II

Polystyrene nanoparticles (PNP) cross rat alveolar epithelial cell monolayers via non-endocytic transcellular pathways. To evaluate epithelial cell type-specificity of PNP trafficking, we studied PNP flux across Madin Darby canine kidney cell II monolayers (MDCK-II). The effects of calcium chelation (EGTA), energy depletion (sodium azide (NaN(3)) or decreased temperature), and endocytosis inhibitors methyl-β-cyclodextrin (MBC), monodansylcadaverine and dynasore were determined. Amidine-modified PNP cross MDCK-II 500 times faster than carboxylate-modified PNP. PNP flux did not increase in the presence of EGTA. PNP flux at 4 °C and after treatment with NaN(3) decreased 75% and 80%, respectively. MBC exposure did not decrease PNP flux, whereas dansylcadaverine- or dynasore-treated MDCK-II exhibited ∼80% decreases in PNP flux. Confocal laser scanning microscopy revealed intracellular colocalization of PNP with clathrin heavy chain. These data indicate that PNP translocation across MDCK-II (1) occurs via clathrin-mediated endocytosis and (2) is dependent on PNP physicochemical properties. We conclude that uptake/trafficking of nanoparticles (NPs) into/across epithelia depends both on properties of the NPs and on the specific epithelial cell type.

Thiolated chitosans: influence of various sulfhydryl ligands on permeation-enhancing and P-gp inhibitory properties

PURPOSE

The influence of various sulfhydryl ligands on permeation-enhancing and P-glycoprotein (P-gp) inhibitory properties of the six established thiolated chitosan conjugates was investigated using Rhodamine-123 (Rho-123) and fluorescein isothiocyanate-dextran 4 (FD4) as model compounds.

METHODS

Permeation of these compounds was tested on freshly excised rat intestine in Ussing-type chambers. Apparent permeability coefficients (Papp) were calculated and compared to values obtained from the buffer only control.

RESULTS

The lyophilized polymers had a thiol group content in the range of 230-520 μmol/g. Results of this study led to the following rank order in permeation enhancement: chitosan-6-mercaptonicotinic acid (chitosan-6MNA) > chitosan-cysteine (chitosan-Cys) > chitosan-glutathione (chitosan-GSH) > chitosan-4-thiobutylamidine (chitosan-TBA) > chitosan-thioglycolic acid (chitosan-TGA) > chitosan-N-acetyl cysteine (chitosan-NAC). In P-gp inhibition studies, 0.5% (m/v) chitosan-NAC showed the highest inhibitory effect on P-gp, where the Papp was determined to be 3.78-fold increased compared with the buffer control. Among these thiolated chitosans, chitosan-NAC and chitosan-6MNA are the most effective polymers being responsible for P-gp inhibition and permeation enhancement, respectively.

CONCLUSION

These thiolated chitosans would therefore be advantageous tools for enhancing the noninvasive bioavailability of active pharmaceutical ingredients.

Lysophosphatidic acid enhances pulmonary epithelial barrier integrity and protects endotoxin-induced epithelial barrier disruption and lung injury

Lysophosphatidic acid (LPA), a bioactive phospholipid, induces a wide range of cellular effects, including gene expression, cytoskeletal rearrangement, and cell survival. We have previously shown that LPA stimulates secretion of pro- and anti-inflammatory cytokines in bronchial epithelial cells. This study provides evidence that LPA enhances pulmonary epithelial barrier integrity through protein kinase C (PKC) delta- and zeta-mediated E-cadherin accumulation at cell-cell junctions. Treatment of human bronchial epithelial cells (HBEpCs) with LPA increased transepithelial electrical resistance (TER) by approximately 2.0-fold and enhanced accumulation of E-cadherin to the cell-cell junctions through Galpha(i)-coupled LPA receptors. Knockdown of E-cadherin with E-cadherin small interfering RNA or pretreatment with EGTA (0.1 mm) prior to LPA (1 microm) treatment attenuated LPA-induced increases in TER in HBEpCs. Furthermore, LPA induced tyrosine phosphorylation of focal adhesion kinase (FAK) and overexpression of the FAK inhibitor, and FAK-related non-kinase-attenuated LPA induced increases in TER and E-cadherin accumulation at cell-cell junctions. Overexpression of dominant negative protein kinase delta and zeta attenuated LPA-induced phosphorylation of FAK, accumulation of E-cadherin at cell-cell junctions, and an increase in TER. Additionally, lipopolysaccharide decreased TER and induced E-cadherin relocalization from cell-cell junctions to cytoplasm in a dose-dependent fashion, which was restored by LPA post-treatment in HBEpCs. Intratracheal post-treatment with LPA (5 microm) reduced LPS-induced neutrophil influx, protein leak, and E-cadherin shedding in bronchoalveolar lavage fluids in a murine model of acute lung injury. These data suggest a protective role of LPA in airway inflammation and remodeling.

Fatty acids increase paracellular absorption of aluminium across Caco-2 cell monolayers

Passive paracellular absorption, regulated by tight junctions (TJs), is the main route for absorption of poorly absorbed hydrophilic substances. Surface active substances, such as fatty acids, may enhance absorption of these substances by affecting the integrity of TJ and increasing the permeability. It has been suggested that aluminium (Al) absorption occurs mainly by the paracellular route. Herein, we investigated if physiologically relevant exposures of fully differentiated Caco-2 cell monolayers to oleic acid and docosahexaenoic acid (DHA), which are fatty acids common in food, increase absorption of Al and the paracellular marker mannitol. In an Al toxicity test, mannitol and Al absorption through Caco-2 cell monolayers were similarly modulated by Al concentrations between 1 and 30mM, suggesting that absorption of the two compounds occurred via the same pathways. Exposure of Caco-2 cell monolayers to non-toxic concentrations of Al (2mM) and (14)C-mannitol in fatty acid emulsions (15 and 30mM oleic acid, 5 and 10mM DHA) caused a decreased transepithelial electrical resistance (TEER). Concomitantly, fractional absorption of Al and mannitol, expressed as percentage of apical Al and mannitol retrieved at the basolateral side, increased with increasing dose of fatty acids. Transmission electron microscopy was applied to assess the effect of oleic acid on the morphology of TJ. It was shown that oleic acid caused a less structured morphology of TJ in Caco-2 cell monolayers. Taken together our findings indicate that fatty acids common in food increase the paracellular intestinal absorption of Al. These findings may influence future risk assessment of human Al exposure.

Cytoskeletal rearrangement and cell death induced by Bothrops alternatus snake venom in cultured Madin–Darby canine kidney cells

Bothrops snake venoms cause renal damage, with renal failure being the main cause of death in humans bitten by these snakes. In this work, we investigated the cytoskeletal rearrangement and cytotoxicity caused by Bothrops alternatus venom in cultured Madin–Darby canine kidney (MDCK) cells. Incubation with venom (10 and 100 µg/mL) significantly (p <0.05) decreased the cellular uptake of neutral red dye after 1 and 3 h. Venom (100 µg/mL) also markedly decreased the transepithelial electrical resistance (RT) across MDCK monolayers. Staining with rhodamine-conjugated phalloidin revealed disarray of the cytoskeleton that involved the stress fibers at the basal cell surface and focal adhesion-associated F-actin in the cell–matrix contact region. Feulgen staining showed a significant decrease in the number of cells undergoing mitosis and an increase in the frequency of altered nuclei. Scanning electron microscopy revealed a decrease in the number of microvilli and the presence of cells with a fusiform format. Flow cytometry with annexin V and propidium iodide showed that cell death occurred by necrosis, with little apoptosis, a conclusion supported by the lack of DNA fragmentation characteristic of apoptosis. Pretreating the cells with catalase significantly attenuated the venom-induced loss of viability, indicating a possible involvement of H2O2 in the cellular damage; less protection was observed with superoxide dismutase or Nω-nitro-l-arginine methyl ester. These results indicate that Bothrops alternatus venom is cytotoxic to cultured MDCK cells, possibly via the action of reactive oxygen species. This cytotoxicity could contribute to nephrotoxicity after envenoming by this species.

Oleic acid and docosahexaenoic acid cause an increase in the paracellular absorption of hydrophilic compounds in an experimental model of human absorptive enterocytes

Surface active compounds present in food possibly have the ability to enhance the absorption of water soluble toxic agents. Therefore, we investigated whether fatty acids such as oleic acid and docosahexaenoic acid (DHA), both commonly present in food, negatively affect the integrity of tight junctions (TJ) in the intestinal epithelium and thereby increase the absorption of poorly absorbed hydrophilic substances. Caco-2 cells, which are derived from human absorptive enterocytes, were grown on permeable filters for 20-25 days. Differentiated cell monolayers were apically exposed for 90min to mannitol in emulsions of oleic acid (5, 15 or 30mM) or DHA (5, 15 or 30mM) in an experimental medium with or without Ca(2+) and Mg(2+). Absorption of (14)C-mannitol increased and trans-epithelial electrical resistance (TEER) decreased in cell monolayers exposed to oleic acid and DHA, compared to controls. Cytotoxicity, measured as leakage of LDH, was higher in groups exposed to 30mM oleic acid and all concentrations of DHA. Morphology of the cell monolayers was studied by using fluorescence microscopy. Exposure of cell monolayers to 5mM DHA for 90min resulted in a profound alteration of the cell-cell contacts as detected by staining the cells for beta-catenin. Oleic acid (30mM) treatment also induced dissolution of the cell-cell contacts but the effect was not as pronounced as with DHA. Cell monolayers were also exposed for 180min to 250nM cadmium (Cd) in emulsions of oleic acid (5 or 30mM) or DHA (1 or 5mM), in an experimental medium with Ca(2+) and Mg(2+). Retention of Cd in Caco-2 cells was higher after exposure to 5mM oleic acid but lower after exposure to 30mM oleic acid and DHA. Absorption of Cd through the monolayers increased after DHA exposure but not after exposure to oleic acid. Our results indicate that fatty acids may compromise the integrity of the intestinal epithelium and that certain lipids in food may enhance the paracellular absorption of poorly absorbed hydrophilic substances.

Cytotoxicity of Lachesis muta muta snake (bushmaster) venom and its purified basic phospholipase A2 (LmTX-I) in cultured cells

Human envenoming by Lachesis muta muta venom, although infrequent, is rather severe, being characterized by pronounced local tissue damage and systemic dysfunctions. Studies on the pharmacological actions of L. m. muta venom are relatively scant and the direct actions of the crude venom and its purified phospholipase A(2) (PLA(2)) have not been addressed using in vitro models. In this work, we investigated the cytotoxicity of L. m. muta venom and its purified PLA(2) isoform LmTX-I in cultured Madin-Darby canine kidney (MDCK) and in a skeletal muscle (C2C12) cell lines. As revealed by neutral red dye uptake assay, the crude venom (10 or 100 microg/ml) induced a significant decrease in cell viability of MDCK cells. LmTX-I at the concentrations tested (70-270 microg/ml or 5-20 microM) displayed no cytotoxicity in both MDCK and C2C12 cell lines. Morphometric analysis of Feulgen nuclear reaction revealed a significant increase in chromatin condensation (pyknosis), apparent reduction in the number of mitotic nuclei and nuclear fragmentation of some MDCK cells after incubation with L. m. muta venom. Monolayer exposure to crude venom resulted in morphological changes as assessed by scanning electron microscopy. The staining with TRITC-labelled phalloidin showed a marked disarray of the actin stress fiber following L. m. muta venom exposure. In contrast, LmTX-I had no effect on nucleus and cell morphologies as well as on stress fiber organization. These results indicate that L. m. muta venom exerts toxic effects on cultured MDCK cells. The LmTX-I probably does not contribute per se to the direct venom cytotoxicity, these effects are mediated by metalloproteinases/disintegrins and other components of the venom.

Calcium signaling complexes in microdomains of polarized secretory cells

The highly polarized nature of epithelial cells in exocrine glands necessitates targeting, assembly into complexes and confinement of the molecules comprising the Ca(2+) signaling apparatus, to cellular microdomains. Such high degree of polarized localization has been shown for all Ca(2+) signaling molecules tested, including G protein coupled receptors and their associated proteins, Ca(2+) pumps, Ca(2+) influx channels at the plasma membrane and Ca(2+) release channels in the endoplasmic reticulum. Although the physiological significance of polarized Ca(2+) signaling is clear, little is known about the mechanism of targeting, assembly and retention of Ca(2+) signaling complexes in cellular microdomains. The present review attempts to summarize the evidence in favor of polarized expression of Ca(2+) signaling proteins at the apical pole of secretory cells with emphasis on the role of scaffolding proteins in the assembly and function of the Ca(2+) signaling complexes. The consequence of polarized enrichment of Ca(2+) signaling complexes at the apical pole is generation of an apical to basal pole gradient of cell responsiveness that, at low physiological agonist concentrations, limits Ca(2+) spikes to the apical pole, and when a Ca(2+) wave occurs, it always propagates from the apical to the basal pole. Our understanding of Ca(2+) signaling in microdomains is likely to increase rapidly with the application of techniques to controllably and selectively disrupt components of the complexes and apply high resolution recording techniques, such as TIRF microscopy to this problem.

Characterisation of adherens and tight junctional molecules in normal animal larynx; determining a suitable model for studying molecular abnormalities in human laryngopharyngeal reflux

BACKGROUND

The disruption of intercellular junctions in the larynx is a pathological feature of laryngopharyngeal reflux (LPR). Good experimental models are necessary to gain greater insight into the molecular mechanisms and alterations that result from abnormal exposure of the laryngeal epithelium to acid refluxate.

AIMS

To characterise laryngeal tissues from different species to determine the most suitable for use in experimental studies of LPR.

METHODS

Human and non-human laryngeal tissues (mouse, rat, guinea pig, porcine, and rabbit) were studied. Histological characterisation was performed by light microscopy. The expression and subcellular localisation of adherens junctional molecules (E-cadherin and beta catenin) was evaluated by immunohistochemistry, and tight junction molecules (occludin and zonula occludens 1 (ZO-1)) by western blotting. The ultrastructural features of porcine and human tissue were assessed by electron microscopy.

RESULTS

Porcine tissue revealed both respiratory-type and stratified squamous epithelium, as seen in the human larynx. The expression and subcellular localisation of the E-cadherin-catenin complex was detected in all species except mouse and rat. The pattern of ZO-1 and occludin expression was preserved in all species.

CONCLUSION

The expression of intercellular junctional complexes in porcine epithelium is similar to that seen in humans. These results confirm the suitability of these species to study molecular mechanisms of LPR in an experimental system.

Permeability of pig urinary bladder wall: the effect of chitosan and the role of calcium

Chitosan is a cationic polysaccharide widely employed as an absorption enhancer. The aim of this work was to examine the effect of chitosan on the permeability of isolated pig urinary bladder wall as well as to determine the role of calcium ions in this process. Besides permeability studies, scanning electron microscopy and fluorescent microscopy were applied to get an insight into the mechanism by which chitosan increases the permeability of urinary bladder wall. Additionally, the obtained findings were compared to the mechanism proposed for Caco-2 cells. The results show that 0.5% (w/v) chitosan increases the permeability of urinary bladder wall by causing the desquamation of the urothelium. Calcium ions, when applied to the luminal surface of the urinary bladder at the same time as chitosan, decreases the effect of chitosan on permeation of the model drug moxifloxacin into the bladder wall in concentration dependent way. The desquamation of urothelium cells caused by chitosan was reduced in the presence of calcium, but not to such extent as it would be expected from the permeability studies. When present, calcium obviously interferes directly in the interactions between chitosan and the surface of urothelium.

Enteropathogenic Escherichia coli outer membrane proteins induce changes in cadherin junctions of Caco-2 cells through activation of PKCalpha

Enteropathogenic Escherichia coli (EPEC) is a Gram-negative bacterial pathogen that adheres to human intestinal epithelial cells, resulting in watery, persistent diarrhoea. Despite the advances made in understanding EPEC-host cell interactions, the molecular mechanisms underlying watery diarrhoea have not been understood fully. Loss of transepithelial resistance and increased monolayer permeability by disruption of tight junctions has been implicated in this process. Apart from disruption of tight junctions, an important factor known to regulate monolayer permeability is E-cadherin and its interaction with beta-catenin, both of which constitute the adherens junctions. Our previous studies using HEp-2 cells demonstrated the morphological and cytoskeletal changes caused by cell-free outer membrane preparations (OMPs) of EPEC. In this study, we have shown that EPEC and its OMP induce significant changes in the adherens junctions of Caco-2 monolayers. We also observed significant phosphorylation of protein kinase Calpha (PKCalpha) in cells treated with either whole EPEC or its OMP. Immunoprecipitation of cell lysates with anti-E-cadherin and probing with phospho-PKCalpha monoclonal antibodies and anti-beta-catenins revealed that in these cells, phosphorylated PKCalpha is associated with cadherins, leading to the dissociation of the cadherin/beta-catenin complex. Immunofluorescence showed beta-catenins dissociated from the membrane-bound cadherins and redistributed into the cytoplasm. Expression of dominant negative PKCalpha reversed these effects caused by either whole EPEC or its OMP and also reduced the associated increase in monolayer permeability. It is possible that this mechanism may complement the earlier known pathways for loss of barrier function involving myosin light chain kinase activation and also may play a role in causing host cell death by apoptosis.

Upregulation of the expression of tight and adherens junction-associated proteins during maturation of neonatal pancreatic islets in vitro

Cell-cell contacts mediated by intercellular junctions are crucial for proper insulin secretion in the endocrine pancreas. The biochemical composition of the intercellular junctions in this organ and the role of junctional proteins in endocrine pancreatic dysfunctions are still unclear. In this study, we investigated the expression and cellular location of junctional and cytoskeletal proteins in cultured neonatal rat pancreatic islets. Neonatal B-cells had an impaired insulin secretion compared to adult cells. Cultured neonatal islets showed a time-dependent increase in the glucose-induced secretory response. The maturation of B-cells in vitro was accompanied by upregulation of the expression of some junctional proteins in islet cells. Neonatal islets cultured for only 24 h showed a low expression and a diffuse cytoplasmic location of the tight junctional proteins occludin and ZO-1 and of the adherens junctional proteins alpha- and beta-catenins, as demonstrated by immunoblotting and immunocytochemistry. Culturing islets for up to 8 days significantly increased the cell expression of these junctional proteins but not of the cytoskeletal proteins vinculin and alpha-actinin. A translocation of ZO-1 and catenins to the cell-cell contact region, as well as a higher association of F-actin with the intercellular junction, were also observed in neonatal islets following prolonged culturing. ZO-1 and beta-catenin were immunolocated in the endocrine pancreas of adult rats indicating that these junctional proteins are also expressed in this organ in situ. In conclusion, endocrine pancreatic cells express several junctional proteins that are upregulated following differentiation of the endocrine pancreas in vitro.

The influence of buffer composition on tissue integrity during permeability experiments "in vitro"

A well-balanced incubation saline is necessary for permeability experiments with the rat jejunal tissue in the diffusion chambers. At the same time the investigated substance must be chemically stable and sufficiently soluble in this incubation saline. To investigate whether the absence of some ions in incubation salines influences the tissue viability and integrity or the diffusional characteristics of the epithelial membrane the electrical parameters were monitored and the permeability of fluorescein and acyclovir was evaluated during the experiments in side-by-side diffusion chambers. Our results show that the tissue integrity and viability are seriously impaired when Ca(2+) and Mg(2+)-free conditions are applied on both sides of the diffusion chambers, but not when only mucosal or only serosal side is Ca(2+) and Mg(2+)-free. Bicarbonate-free incubation salines can also alter the measured apparent permeability coefficients even though the tissue viability and integrity do not change. This change in the apparent permeability is most likely due to a change in the pH of the mucosal surface and can be prevented if the buffer capacity of the incubation saline is increased.

Engineering of dendrimer surfaces to enhance transepithelial transport and reduce cytotoxicity

PURPOSE

To evaluate the cytotoxicity, permeation, and transport mechanisms of PAMAM dendrimers and surface-modified cationic PAMAM dendrimers using monolayers of the human colon adenocarcinoma cell line, Caco-2.

METHODS

Cytotoxicity was determined using the MTT assay. The effect of dendrimers on monolayer integrity was determined from measurements of transepithelial electrical resistance (TEER) and [14C]mannitol apparent permeability coefficient (Papp). The Papp of dendrimers through monolayers was measured in both the apical (A)-to-basolateral (B) and B --> A directions at 4 degrees C and 37 degrees C and also in the presence and absence of ethylenediamine tetraacetic acid (EDTA) and colchicine.

RESULTS

The cytotoxicity and permeation of dendrimers increased with both concentration and generation. The cytotoxicity of cationic dendrimers (G2, G3, G4) was greater than that of anionic dendrimers (G2.5, G3.5) but was reduced by conjugation with lauroyl chloride: the least cytotoxic conjugates were those with six attached lauroyl chains. At 37 degrees C the Papp of cationic dendrimers was higher than that of anionic dendrimers and, in general, increased with the number of attached lipid chains. Cationic dendrimers decreased TEER and significantly increased the Papp of mannitol. Modified dendrimers also reduced TEER and caused a more marked increase in the Papp of mannitol. The Papp values of dendrimers and modified dendrimers were higher in the presence of EDTA, lower in the presence of colchicine, and lower at 4 degrees C than at 37 degrees C.

CONCLUSIONS

The properties of dendrimers may be significantly modified by surface engineering. Conjugation of cationic PAMAM dendrimers with lauroyl chloride decreased their cytotoxicity and increased their permeation through Caco-2 cell monolayers. Both PAMAM dendrimers and lauroyl-PAMAM dendrimer conjugates can cross epithelial monolayers by paracellular and transcellular pathways.

Disruption of cell polarity by enteropathogenic Escherichia coli enables basolateral membrane proteins to migrate apically and to potentiate physiological consequences

Enteropathogenic Escherichia coli (EPEC) disrupts the structure and barrier function of host intestinal epithelial tight junctions (TJs). The impact of EPEC on TJ "fence function," i.e., maintenance of cell polarity, has not been investigated. In polarized cells, proteins such as beta(1)-integrin and Na(+)/K(+) ATPase are restricted to basolateral (BL) membranes. The outer membrane EPEC protein intimin possesses binding sites for the EPEC translocated intimin receptor (Tir) and beta(1)-integrin. Restriction of beta(1)-integrin to BL domains, however, precludes opportunity for interaction. We hypothesize that EPEC perturbs TJ fence function and frees BL proteins such as beta(1)-integrin to migrate to apical (AP) membranes of host cells, thus allowing interactions with bacterial adhesins such as intimin. The aim of this study was to determine whether EPEC alters the polar distribution of BL proteins, in particular beta(1)-integrin, and if such redistribution contributes to pathogenesis. Human intestinal epithelial T84 cells and EPEC strain E2348/69 were used. Selective biotinylation of AP or BL membrane proteins and confocal microscopy showed the presence of beta(1)-integrin and Na(+)/K(+) ATPase on the AP membrane following infection. beta(1)-Integrin antibody afforded no protection against the initial EPEC-induced decrease in transepithelial electrical resistance (TER) but halted the progressive decrease at later time points. While the effects of EPEC on TJ barrier and fence function were Tir dependent, disruption of cell polarity by calcium chelation allowed a tir mutant to be nearly as effective as wild-type EPEC. In contrast, deletion of espD, which renders the type III secretory system ineffective, had no effect on TER even after calcium chelation, suggesting that the putative beta(1)-integrin-intimin interaction serves to provide intimate contact, like that of Tir and intimin, making translocation of effector molecules more efficient. We conclude that the initial alterations of TJ barrier and fence function by EPEC are Tir dependent but that later disruption of cell polarity and accessibility of EPEC to BL membrane proteins, such as beta(1)-integrin, potentiates the physiological perturbations.

Regulation of adherens junctions and epithelial paracellular permeability: a novel function for polyamines

Maintenance of intestinal mucosal epithelial integrity requires polyamines that are involved in the multiple signaling pathways controlling gene expression and different epithelial cell functions. Integrity of the intestinal epithelial barrier depends on a complex of proteins composing different intercellular junctions, including tight junctions, adherens junctions, and desmosomes. E-cadherin is primarily found at the adherens junctions and plays a critical role in cell-cell adhesions that are fundamental to formation of the intestinal epithelial barrier. The current study determined whether polyamines regulate intestinal epithelial barrier function by altering E-cadherin expression. Depletion of cellular polyamines by alpha-difluoromethylornithine (DFMO) reduced intracellular free Ca2+ concentration ([Ca2+]cyt), decreased E-cadherin expression, and increased paracellular permeability in normal intestinal epithelial cells (IEC-6 line). Polyamine depletion did not alter expression of tight junction proteins such as zona occludens (ZO)-1, ZO-2, and junctional adhesion molecule (JAM)-1. Addition of exogenous polyamine spermidine reversed the effects of DFMO on [Ca2+]cyt and E-cadherin expression and restored paracellular permeability to near normal. Elevation of [Ca2+]cyt by the Ca2+ ionophore ionomycin increased E-cadherin expression in polyamine-deficient cells. In contrast, reduction of [Ca2+]cyt by polyamine depletion or removal of extracellular Ca2+ not only inhibited expression of E-cadherin mRNA but also decreased the half-life of E-cadherin protein. These results indicate that polyamines regulate intestinal epithelial paracellular barrier function by altering E-cadherin expression and that polyamines are essential for E-cadherin expression at least partially through [Ca2+]cyt.

Novel complexation hydrogels for oral peptide delivery: in vitro evaluation of their cytocompatibility and insulin-transport enhancing effects using Caco-2 cell monolayers

Poly[methacrylic acid-grafted-poly(ethylene glycol)] [P(MAA-g-EG)] is a complexation hydrogel molecularly designed for oral peptide delivery. In this work, the cytotoxicity and insulin-transport enhancing effect of P(MAA-g-EG) microparticles on intestinal epithelial cells were evaluated using Caco-2 cell monolayers. A series of P(MAA-g-EG) microparticles with different polymer compositions were prepared by a photo-initiated free radical solution polymerization and subsequent pulverization. The hydrogel microparticles were preswollen in either Ca2+-containing (CM+) or Ca2+-free medium (CM-; pH 7.4) and applied to the apical side of the Caco-2 monolayers. No significant cytotoxic effects, as determined by a calorimetric assay with P(MAA-g-EG) microparticles preswollen in the CM+, were observed at doses ranging from 3 to 31 mg/cm2 of cell monolayer. Transepithelial electrical resistance (TEER) measurements showed that the P(MAA-g-EG) microparticles induced a Ca2+ concentration-dependent lowering in TEER values. The reduction effect in CM- media was greater than that in CM+ media (17 +/- 2% reduction in CM+ and 45 +/- 3% reduction in CM-, respectively). Insulin transport in the presence of the preswollen P(MAA-g-EG) microparticles was also strongly depended on the Ca2+ concentration in the medium. The respective estimated permeability for insulin alone and the insulin with hydrogels in CM+ were 0.77 and 1.16 x 10(-8) cm/s, whereas those in CM- were 1.18 and 24.78 x 10(-8) cm/s. The results demonstrate that the P(MAA-g-EG) hydrogel microparticles could be used as a cytocompatible carrier possessing the transport-enhancing effect of insulin on the intestinal epithelial cells.

Effects of various absorption enhancers on transport of clodronate through Caco-2 cells

The major disadvantage concerning clinical use of bishosphonate drugs, like clodronate, is their poor and variable absorption after oral administration. The objective of this study was to assess the effects of four different absorption enhancers-palmitoyl carnitine chloride (PCC), N-trimethyl chitosan chloride (TMC), sodium caprate (C10), and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-on the transport of clodronate using Caco-2 cell culture model. The transport experiments were performed in a normal (1.3mM) and in a minimum-calcium concentration (apically calcium-free medium and basolaterally 100 microM calcium concentration). In the normal calcium concentration, a strong enhancement in clodronate permeation was observed with the enhancers: EGTA (2.5mM), TMC (1.5% w/v), and PCC (0.2mM) increased the transport of 1mM clodronate 190-, 20-, and 10-fold, respectively, and the transport of 10mM clodronate 130-, 70-, and 35-fold. In the minimum-calcium concentration, the effects of the absorption enhancers on the transport of clodronate were not so potent: TMC, PCC, and EGTA caused 2- to 20-fold enhancement in clodronate permeation whereas C10 (10mM) was without any effect. According to the results, the permeation of clodronate through Caco-2 cells could be significantly promoted by the absorption enhancers, which cause widening of the tight junctions and, thus, increase the permeability of the paracellular route.

Effects of cadmium on E-cadherin and VE-cadherin in mouse lung

Exposure to Cd(2+) via inhalation or intratracheal instillation results in pulmonary edema, which is followed by the influx of leukocytes, the proliferation of type II pneumocytes and eventual scarring and fibrotic changes. While the general toxic effects of Cd(2+) in the lung have been well characterized, the specific molecular mechanisms underlying these effects have yet to be elucidated. Previously we have shown that Cd(2+) can disrupt the adhering junctions between various types of epithelial and endothelial cells in culture, most likely by perturbing the function of the Ca(2+) dependent cell adhesion molecules E-cadherin and VE-cadherin respectively. The objectives of this study were to determine whether respiratory exposure to Cd(2+) can alter the localization of E-cadherin and VE-cadherin in the lung, and to determine whether this effect may play a role in the acute pneumotoxic response to Cd(2+). Male CF-1 mice were exposed to CdCl(2) (0, 16.25, 32.5, 65 or 130 nmoles in 50 microl saline) via intratracheal instillation. After 24 hours, the lungs were removed and either subjected to bronchoalveolar lavage or analyzed for histopathologic changes. The results showed that Cd(2+) caused an increase in lung weight and in the protein content of the lavage fluid. These effects were accompanied by a pronounced decrease in the amount of E-cadherin in epithelial cells of the alveoli and small bronchioles and of VE-cadherin in vascular endothelial cells. Assessment of cell membrane integrity with ethidium homodimer-1 showed no evidence of severe injury or death in alveolar epithelial cells. These findings suggest that E-cadherin and VE-cadherin may be important early targets of Cd(2+) toxicity in the lung.

Single-cell epithelial defects close rapidly by an actinomyosin purse string mechanism with functional tight junctions

Restitution of single-cell defects, a frequent event in epithelia with high turnover, is poorly understood. Morphological and functional changes were recorded, using intravital time-lapse video microscopy, confocal fluorescence microscopy, and conductance scanning techniques. After artificial single-cell loss from an HT-29/B6 colonic cell monolayer, the basal ends of adjacent cells extended. Concurrently, the local conductive leak associated with the defect sealed with an exponential time course (from 0.48 +/- 0.05 microS 2 min post lesion to 0.17 +/- 0.02 microS 8 min post lesion, n = 17). Between 3 and 10 min post lesion, a band of actin arose around the gap, which colocalized with a ring of ZO-1 and occludin. Hence, tight junction proteins bound to the actin band facing the gap, and competent tight junctions assembled in the adjoining cell membranes. Closure and sealing were inhibited when actin polymerization was blocked by cytochalasin D, delayed following decrease of myosin-ATPase activity by butanedione monoxime, and blocked after myosin light chain kinase inhibition by ML-7. The Rho-associated protein kinase inhibitor Y-27632 did not affect restitution. After loosening of intercellular contacts in low Ca(2+) Ringer solution, the time course of restitution was not significantly altered. Albeit epithelial conductivity was 12-fold higher in low Ca(2+) Ringer solution than in controls, under both conditions the repaired epithelium assumed the same conductivity as distant intact epithelium. In conclusion, epithelial restitution of single-cell defects comprises rapid closure by an actinomyosin 'purse-string' mechanism and simultaneous formation of a functional barrier from tight junction proteins also associated with the purse string.

Impairment of the cell-to-matrix adhesion and cytotoxicity induced by Bothrops moojeni snake venom in cultured renal tubular epithelia

Bothrops moojeni snake venom induces acute renal failure (ARF) as a consequence of morphological and functional alterations in glomerular and tubular cells. It is still unclear whether the ARF results from a direct cytotoxic effect on renal epithelia or from a renal ischemia due to systemic hemodynamic disturbances. This work investigated the in vitro effect of B. moojeni crude venom, using cultured Madin-Darby canine kidney (MDCK) monolayers as a model. The crude venom induced a significant time- and dose-dependent decrease in transepithelial electrical resistance across MDCK monolayers. In addition, the exposure to the venom resulted in cell detachment from the substratum, as revealed by transmission electron microscopy. Immunocytochemical analysis showed no change in the distribution of some junctional proteins, such as occludin, ZO-1, and E-cadherin. Nevertheless, the staining with labeled phalloidin revealed a disarray of the cytoskeleton, specifically of the stress fibers and of the focal adhesion-associated F-actin at the cell-to-matrix contact region. The treatment with B. moojeni venom also increased the cell release of lactate dehydrogenase and decreased cellular uptake of the vital neutral red. In conclusion, B. moojeni crude venom appears to have a direct cytotoxic effect on a renal tubule-derived cell line, also inducing impairment of the cell-matrix interaction.

Chlamydia trachomatis disrupts N-cadherin-dependent cell-cell junctions and sequesters beta-catenin in human cervical epithelial cells

The cadherin/catenin complex serves as an important structural component of adherens junctions in epithelial cells. Under certain conditions, beta-catenin can be released from this complex and interact with transcription factors in the nucleus to stimulate the expression of genes that regulate apoptosis and cell cycle control. While studying the effects of the bacterial pathogen Chlamydia trachomatis on human cervical epithelial cells in culture, we observed that C. trachomatis caused the epithelial cells to separate from each other without detaching from their growing surface. The objective of the present study was to determine if this effect might involve the disruption of the cadherin/catenin complex. Primary cultures of human cervical epithelial cells or HeLa cells were infected with C. trachomatis serovar E. Cadherin-like immunoreactive materials and beta-catenin were visualized by immunofluorescence. Preliminary studies showed that N-cadherin was the primary cadherin expressed in both the primary cultures and the HeLa cells. In noninfected cells, N-cadherin and beta-catenin were colocalized at the intercellular junctional complexes. By contrast, the infected cells showed a marked loss of both N-cadherin and beta-catenin labeling from the junctional complexes and the concomitant appearance of intense beta-catenin labeling associated with the chlamydial inclusion. The results of Western blot analyses of extracts of C. trachomatis showed no evidence of cross-reactivity with the beta-catenin antibody. These results indicate that C. trachomatis causes the breakdown of the N-cadherin/beta-catenin complex and that the organism can sequester beta-catenin within the chlamydial inclusion. This could represent an important mechanism by which C. trachomatis alters epithelial cell function.

Oral drug absorption enhancement by chitosan and its derivatives

Chitosan is a non-toxic, biocompatible polymer that has found a number of applications in drug delivery including that of absorption enhancer of hydrophilic macromolecular drugs. Chitosan, when protonated (pH<6.5), is able to increase the paracellular permeability of peptide drugs across mucosal epithelia. Chitosan derivatives have been evaluated to overcome chitosan's limited solubility and effectiveness as absorption enhancer at neutral pH values such as those found in the intestinal tract. Trimethyl chitosan chloride (TMC) has been synthesized at different degrees of quaternization. This quaternized polymer forms complexes with anionic macromolecules and gels or solutions with cationic or neutral compounds in aqueous environments and neutral pH values. TMC has been shown to considerably increase the permeation and/or absorption of neutral and cationic peptide analogs across intestinal epithelia. The mechanism by which TMC enhances intestinal permeability is similar to that of protonated chitosan. It reversibly interacts with components of the tight junctions, leading to widening of the paracellular routes. Mono-carboxymethylated chitosan (MCC) is a polyampholytic polymer, able to form visco-elastic gels in aqueous environments or with anionic macromolecules at neutral pH values. MCC appears to be less potent compared to the quaternized derivative. Nevertheless, MCC was found to increase the permeation and absorption of low molecular weight heparin (LMWH; an anionic polysaccharide) across intestinal epithelia. Neither chitosan derivative provokes damage of the cell membrane, and therefore they do not alter the viability of intestinal epithelial cells.

Evidence that increased tyrosine phosphorylation causes disassembly of adherens junctions but does not perturb paracellular permeability in Caco-2 cells

In this study, we report on the apparent effect of increased tyrosine phosphorylation events on the assembly and integrity of adherens junctions (AJs) and on paracellular permeability in Caco-2 cells. Cell monolayers were incubated with the phosphotyrosine phosphatase inhibitor vanadate/H2O2. Addition of this compound to monolayer resulted in disruption of the AJs, as revealed by electron microscopy and by a loss of membrane association of the AJ-associated protein uvomorulin/E-cadherin (U/E-c). However, tight junctions (TJs) were unaltered, as determined by measuring the transepithelial resistance (Rt), by ruthenium red labeling, as seen by transmission electron microscopy, and the distribution of TJ strands as seen in freeze-fracture replicas and by hyperphosphorylation of triton-insoluble occludin. Also examination of vanadate/H2O2 treated cells indicated a specific increase in AJ-associated phosphotyrosine residues as evaluated by immunofluorescence microscopy, but no modification of F-actin distribution, as revealed by confocal laser scanning microscopy analysis. To verify that modulation of AJs was indeed related to tyrosine phosphorylation, we tested a range of distinct protein kinase inhibitors. Of the three inhibitors tested (tyrphostin 25, genistein and staurosporine), tyrphostin 25 completely blocked the effects of vanadate/ H2O2 on assembly and integrity of AJs, redistribution of U/E-c and phosphotyrosine labeling. Our results indicate that, after addition of vanadate/H2O2 to Caco-2 monolayers, specific tyrosine phosphorylation of proteins cause disruption of AJs, but no modifications of the TJs' structure and functionality. These observations suggest that, in contrast to what happens with epithelial cells, TJs and AJs of Caco-2 cells are regulated by independent mechanisms.

Chitosan and its derivatives as intestinal absorption enhancers

Chitosan is a non-toxic, biocompatible polymer that has found a number of applications in drug delivery including that of absorption enhancer of hydrophilic macromolecular drugs. Chitosan, when protonated (pH<6.5), is able to increase the paracellular permeability of peptide drugs across mucosal epithelia. Chitosan derivatives have been evaluated to overcome chitosan's limited solubility and effectiveness as absorption enhancer at neutral pH values such as those found in the intestinal tract. Trimethyl chitosan chloride (TMC) has been synthesized at different degrees of quaternization. This quaternized polymer forms complexes with anionic macromolecules and gels or solutions with cationic or neutral compounds in aqueous environments and neutral pH values. TMC has been shown to considerably increase the permeation of neutral and cationic peptide analogs across Caco-2 intestinal epithelia. The mechanism by which TMC is enhancing the intestinal permeability is similar to that of protonated chitosan. It reversibly interacts with components of the tight junctions, leading to widening of the paracellular routes. This chitosan derivative does not provoke damage of the cell membrane, and does not alter the viability of intestinal epithelial cells. Co-administrations of TMC with peptide drugs were found to substantially increase the bioavailability of the peptide in both rats and juvenile pigs compared with administrations without the polymer.

Modulation of gap and adherens junctional proteins in cultured neonatal pancreatic islets

Fetal and neonatal pancreatic islets have lower insulin secretory responses compared with adult islets. In culture conditions and after treatment with mammosomatotropic hormones, neonatal islets undergo maturation of the secretory machinery that might involve regulation of cell-cell contacts within the islet. This study is an investigation of the effect of prolonged culturing and in vitro treatment with prolactin on the expression of the gap junction-associated connexin 43 and the adherens junction-associated beta-catenin in cultured neonatal rat islets. Pancreatic islets from neonatal Wistar rats were cultured for 24 hours or 7 days, and the treated group was exposed to 2 microg/mL prolactin daily for 7 days. Connexin 43 and beta-catenin were barely detected at the cell-cell contacts in 24-hour-cultured islets, as revealed by immunocytochemical analysis. Nevertheless, both junctional proteins were well expressed at the junctional region in islet cells cultured for 7 days and showed even greater staining in islets after long-term prolactin treatment. In accordance with the morphologic data, neonatal islets cultured for 24 hours displayed a relatively low level of connexin 43, as determined by Western blot analysis. Culturing for 7 days or combined prolactin treatment induced a significant increase in connexin 43 expression; this was 40% greater in the prolactin-treated group than in the control group. Furthermore, an enhancement of the expression of beta-catenin and translocation of this protein to the cell-cell contact site was also observed in neonatal islets cultured for 7 days compared with those cultured for 24 hours. In vitro prolactin treatment induced even greater expression of beta-catenin in islet cells. A correlation was observed between the increased expression of these junctional proteins and an increase in insulin secretion in cultured neonatal islets. In conclusion, prolonged culturing and in vitro treatment with prolactin induce the modulation of gap and adherens junctional proteins in pancreatic islets, which may be an important event in the in vitro maturation process of neonatal islet cells.

Functional modeling of tight junctions in intestinal cell monolayers using polyethylene glycol oligomers

Despite significant advances in the characterization of tight junction (TJ) proteins, little is known about how molecular changes relate to function due primarily to the limitations of conventional paracellular probes. To address this, the paracellular pathway in Caco-2 and T84 cell lines was profiled by measuring the permeabilities of 24 polyethylene glycols (PEG) of increasing molecular radius (3.5--7.4 A) analyzed by mass spectrometry. When combined with a paracellular sieving model, these data provided quantitative descriptors of the pathway under control conditions and after exposure to TJ modulators. PEG profiles in both cell lines conformed to a biphasic process involving a restrictive pore (radius 4.3--4.5 A) and a nonrestrictive component responsible for permeability of larger molecules. PEG profiling revealed significant differences between the effects of EGTA and sodium caprate (C10). The restrictive component of EGTA-treated cells lost all size discrimination due to an increase in pore radius. Sodium caprate had no effect on pore radius but increased permeability via a different mechanism possibly involving increased numbers of functional pores. PEG profiling provides a useful tool for probing the functional regulation of the paracellular route.

Enhancing paracellular permeability by modulating epithelial tight junctions

The intestinal epithelium is a major barrier to the absorption of hydrophilic drugs. The presence of intercellular junctional complexes, particularly the tight junctions (zona occludens), renders the epithelium impervious to hydrophilic drugs, which cannot diffuse across the cells through the lipid bilayer of the cell membranes. There have been significant advances in understanding the structure and cellular regulation of tight junctions over the past decade. This article reviews current knowledge regarding the physiological regulation of tight junctions and paracellular permeability, and recent progress towards the rational design of agents that can effectively and safely increase paracellular permeability via modulation of tight junctions.

Evidence that E-cadherin may be a target for cadmium toxicity in epithelial cells

E-cadherin is a Ca(2+)-dependent cell adhesion molecule that plays an important role in the development and maintenance of epithelial polarity and barrier function. This commentary describes the results of recent studies showing that the environmental pollutant Cd(2+) can damage the E-cadherin-dependent junctions between many types of epithelial cells and reviews the evidence indicating that this effect results from the direct interaction of Cd(2+) with the E-cadherin molecule. In addition, the implications of these findings with respect to the mechanisms of Cd(2+) toxicity in specific target organs such as lung, kidney, bone, and the vascular endothelium are discussed.

In vitro transepithelial drug transport by on-line measurement: cellular control of paracellular and transcellular transport

Studies on transcellular transport across epithelial cell layers are performed mostly by discontinuous sampling of the transported compound. This has several drawbacks, e.g., it gives disturbances in volume, it limits the time-resolution, and is often laborious. In this report we introduce a method to measure transepithelial transport of fluorescent compounds continuously. The time-resolution is at the (sub)minute scale, allowing the measurement of the change in transport rate before and after transport modulation. We will describe how we used the method to measure transcellular and paracellular transport. For highly membrane-impermeable compounds, the paracellular transport and the regulation of the tight junctions was studied in wild-type and MDR1 cDNA transfected epithelial canine kidney cells (MDCKII). The effect of the multidrug transporter P-glycoprotein (Pgp) on the transepithelial transport was studied. Addition of the Pgp inhibitor SDZ PSC 833 showed a modulation of the idarubicin (IDA) and daunorubicin (DNR) transport, which was larger during transport from the basolateral to the apical side than in the reverse direction. By modeling the transepithelial transport, we found that in these cells Pgp had more effect on the basolateral to apical transport than vice versa, which can be attributed to a relatively large passive permeation coefficient for the cellular basolateral plasma membrane.

Regulation of the intestinal epithelial paracellular barrier

Paracellular transport of orally-administered drugs, the passage of molecules between adjacent intestinal epithelial cells, is impeded by a range of structural and functional features found in the intestine. An increased knowledge of the mechanisms that govern the paracellular barrier will enable the pharmaceutical scientist to design novel and rational formulations and delivery platforms that will improve the oral bioavailability of therapeutic molecules, particularly proteins and peptides, which would be taken-up by the paracellular pathway.