Regulation of tight junction permeability by calcium mediators and cell cytoskeleton in rabbit tracheal epithelium

The role of environmental calcium in the extreme acid tolerance of northern banjo frog (Limnodynastes terraereginae) larvae

Many aquatically respiring animals acutely exposed to low pH waters suffer inhibition of ion uptake, and loss of branchial (gill) epithelial integrity, culminating in a fatal loss of body Na+. Environmental calcium levels ([Ca2+]e) are pivotal in maintaining branchial junction integrity, with supplemental Ca2+ reversing the negative effects of low pH in some animals. Tolerance of some naturally acidic environments by aquatic animals is further complicated by low [Ca2+]e, yet many of these environments are surprisingly biodiverse. How animals overcome the damaging actions of low pH and low environmental Ca2+ remains unknown. We examined the effects of [Ca2+]e on the response to low pH in larvae of the highly acid tolerant frog Limnodynastes terraereginae. Acute exposure to low pH water in the presence of low (5 µmol L-1) [Ca2+]e increased net Na+ efflux. Provision of additional [Ca2+]e reduced net Na+ efflux, but the effect was saturable. Acclimation to both low and high (250 µmol L-1) [Ca2+]e improved the resistance of larvae to Na+ efflux at low pH. Exposure to the Ca2+ channel inhibitor ruthenium red resulted in an abrupt loss of tolerance in low pH acclimated larvae. Acclimation to acidic water increased branchial gene expression of the intracellular Ca2+ transport protein calbindin, consistent with a role for increased transcellular Ca2+ trafficking in the tolerance of acidic water. This study supports a role for [Ca2+]e in promoting branchial integrity and highlights a potential mechanism via the maintenance of transcellular Ca2+ uptake in the acid tolerance of L. terraereginae larvae.

HCMV-Mediated Interference of Bortezomib-Induced Apoptosis in Colon Carcinoma Cell Line Caco-2

Human cytomegalovirus (HCMV) has been implicated in the development of human malignancies, for instance in colon cancer. Proteasome inhibitors were developed for cancer therapy and have also been shown to influence HCMV infection. The aim of this study was to investigate if proteasome inhibitors have therapeutic potential for colon carcinoma and how this is influenced by HCMV infection. We show by immunofluorescence and flow cytometry that the colon carcinoma cell line Caco-2 is susceptible to HCMV infection. Growth curve analysis as well as protein expression kinetics and quantitative genome analysis further confirm these results. HCMV has an anti-apoptotic effect on Caco-2 cells by inhibiting very early events of the apoptosis cascade. Further investigations showed that HCMV stabilizes the membrane potential of the mitochondria, which is typically lost very early during apoptosis. This stabilization is resistant to proteasome inhibitor Bortezomib treatment, allowing HCMV-infected cells to survive apoptotic signals. Our findings indicate a possible role of proteasome inhibitors in colon carcinoma therapy.

Suitability and functional characterization of two Calu-3 cell models for prediction of drug permeability across the airway epithelial barrier

The Calu-3 cell line has been largely investigated as a physiological and pharmacological model of the airway epithelial barrier. Its suitability for prediction of drug permeability across the airway epithelia, however, has not been yet evaluated by using large enough set of model drugs. We evaluated two Calu-3 cell models (air-liquid and liquid-liquid) for drug permeability prediction based on the recent regulatory guidelines on showing suitability of in vitro permeability methods for drug permeability classification. Bidirectional permeability assays using 22 model drugs and several zero permeability markers, as well as using ABC transporter substrates were conducted. Functional activity of P-gp, but not of BCRP was revealed. The potential of the Calu-3 cells to be used as a model of the nasal epithelial barrier, despite their different anatomical origin, has been demonstrated by the obtained excellent correlation with the fully differentiated 3D human nasal epithelial model (MucilAir™) for 11 model drugs, as well as by the good correlation obtained with the human nasal epithelial cell line RPMI 2650. In addition, the permeability values determined in the two Calu-3 models correlated well with the intestinal permeability model Caco-2.

Imaging effects of hyperosmolality on individual tricellular junctions

The use of hyperosmolar agents (osmotherapy) has been a major treatment for intracranial hypertension, which occurs frequently in brain diseases or trauma. However, side-effects of osmotherapy on the brain, especially on the blood-brain barrier (BBB) are still not fully understood. Hyperosmolar conditions, termed hyperosmolality here, are known to transiently disrupt the tight junctions (TJs) at the endothelium of the BBB resulting in loss of BBB function. Present techniques for evaluation of BBB transport typically reveal aggregated responses from the entirety of BBB transport components, with little or no opportunity to evaluate heterogeneity present in the system. In this study, we utilized potentiometric-scanning ion conductance microscopy (P-SICM) to acquire nanometer-scale conductance maps of Madin-Darby Canine Kidney strain II (MDCKII) cells under hyperosmolality, from which two types of TJs, bicellular tight junctions (bTJs) and tricellular tight junctions (tTJs), can be visualized and differentiated. We discovered that hyperosmolality leads to increased conductance at tTJs without significant alteration in conductance at bTJs. To quantify this effect, an automated computer vision algorithm was designed to extract and calculate conductance components at both tTJs and bTJs. Additionally, lowering Ca2+ concentration in the bath facilitates tTJ disruption under hyperosmolality. Strengthening tTJ structure by overexpressing immunoglobulin-like domain-containing receptor 1 (ILDR1) protein abrogates the effect of hyperosmolality. We posit that osmotic stress physically disrupts tTJ structure, as evidenced by super-resolution microscopy. Findings from this study not only provide a high-resolution view of TJ structure and function, but also can inform current osmotherapy and drug delivery strategies for brain diseases.

Improved In Vitro Model for Intranasal Mucosal Drug Delivery: Primary Olfactory and Respiratory Epithelial Cells Compared with the Permanent Nasal Cell Line RPMI 2650

Background: The epithelial layer of the nasal mucosa is the first barrier for drug permeation during intranasal drug delivery. With increasing interest for intranasal pathways, adequate in vitro models are required. Here, porcine olfactory (OEPC) and respiratory (REPC) primary cells were characterised against the nasal tumour cell line RPMI 2650. Methods: Culture conditions for primary cells from porcine nasal mucosa were optimized and the cells characterised via light microscope, RT-PCR and immunofluorescence. Epithelial barrier function was analysed via transepithelial electrical resistance (TEER), and FITC-dextran was used as model substance for transepithelial permeation. Beating cilia necessary for mucociliary clearance were studied by immunoreactivity against acetylated tubulin. Results: OEPC and REPC barrier models differ in TEER, transepithelial permeation and MUC5AC levels. In contrast, RPMI 2650 displayed lower levels of MUC5AC, cilia markers and TEER, and higher FITC-dextran flux rates. Conclusion: To screen pharmaceutical formulations for intranasal delivery in vitro, translational mucosal models are needed. Here, a novel and comprehensive characterisation of OEPC and REPC against RPMI 2650 is presented. The established primary models display an appropriate model for nasal mucosa with secreted MUC5AC, beating cilia and a functional epithelial barrier, which is suitable for long-term evaluation of sustained release dosage forms.

Enhancing glucose flux into sweat by increasing paracellular permeability of the sweat gland

Non-invasive wearable biosensors provide real-time, continuous, and actionable health information. However, difficulties detecting diluted biomarkers in excreted biofluids limit practical applications. Most biomarkers of interest are transported paracellularly into excreted biofluids from biomarker-rich blood and interstitial fluid during normal modulation of cellular tight junctions. Calcium chelators are reversible tight junction modulators that have been shown to increase absorption across the intestinal epithelium. However, calcium chelators have not yet been shown to improve the extraction of biomarkers. Here we show that for glucose, a paracellularly transported biomarker, the flux into sweat can be increased by >10x using citrate, a calcium chelator, in combination with electroosmosis. Our results demonstrate a method of increasing glucose flux through the sweat gland epithelium, thereby increasing the concentration in sweat. Future work should examine if this method enhances flux for other paracellularly transported biomarkers to make it possible to detect more biomarkers with currently available biosensors.

Bordetella pertussis Adenylate Cyclase Toxin Disrupts Functional Integrity of Bronchial Epithelial Layers

The airway epithelium restricts the penetration of inhaled pathogens into the underlying tissue and plays a crucial role in the innate immune defense against respiratory infections. The whooping cough agent, Bordetella pertussis, adheres to ciliated cells of the human airway epithelium and subverts its defense functions through the action of secreted toxins and other virulence factors. We examined the impact of B. pertussis infection and of adenylate cyclase toxin-hemolysin (CyaA) action on the functional integrity of human bronchial epithelial cells cultured at the air-liquid interface (ALI). B. pertussis adhesion to the apical surface of polarized pseudostratified VA10 cell layers provoked a disruption of tight junctions and caused a drop in transepithelial electrical resistance (TEER). The reduction of TEER depended on the capacity of the secreted CyaA toxin to elicit cAMP signaling in epithelial cells through its adenylyl cyclase enzyme activity. Both purified CyaA and cAMP-signaling drugs triggered a decrease in the TEER of VA10 cell layers. Toxin-produced cAMP signaling caused actin cytoskeleton rearrangement and induced mucin 5AC production and interleukin-6 (IL-6) secretion, while it inhibited the IL-17A-induced secretion of the IL-8 chemokine and of the antimicrobial peptide beta-defensin 2. These results indicate that CyaA toxin activity compromises the barrier and innate immune functions of Bordetella-infected airway epithelia.

Ocular Drug Delivery Barriers-Role of Nanocarriers in the Treatment of Anterior Segment Ocular Diseases

Ocular drug delivery is challenging due to the presence of anatomical and physiological barriers. These barriers can affect drug entry into the eye following multiple routes of administration (e.g., topical, systemic, and injectable). Topical administration in the form of eye drops is preferred for treating anterior segment diseases, as it is convenient and provides local delivery of drugs. Major concerns with topical delivery include poor drug absorption and low bioavailability. To improve the bioavailability of topically administered drugs, novel drug delivery systems are being investigated. Nanocarrier delivery systems demonstrate enhanced drug permeation and prolonged drug release. This review provides an overview of ocular barriers to anterior segment delivery, along with ways to overcome these barriers using nanocarrier systems. The disposition of nanocarriers following topical administration, their safety, toxicity and clinical trials involving nanocarrier systems are also discussed.

Oral uptake of nanoparticles: human relevance and the role of in vitro systems

Nanoparticles (NPs) present in environment, consumer and health products, food and medical applications lead to a high degree of human exposure and concerns about potential adverse effects on human health. For the general population, the exposure through contact with the skin, inhalation and oral uptake are most relevant. Since in vivo testing is only partly able to study the effects of human oral exposure, physiologically relevant in vitro systems are being developed. This review compared the three routes taking into account the estimated concentration, size of the exposed area, morphology of the involved barrier and translocation rate. The high amounts of NPs in food, the large absorption area and the relatively high translocation rate identified oral uptake as most important portal of entry for NPs into the body. Changes of NP properties in the physiological fluids, mechanisms to cross mucus and epithelial barrier, and important issues in the use of laboratory animals for oral exposure are mentioned. The ability of in vitro models to address the varying conditions along the oro-gastrointestinal tract is discussed, and requirements for physiologically relevant in vitro testing of orally ingested NPs are listed.

Drug Permeation Characterization of Inhaled Dry Powder Formulations in Air-Liquid Interfaced Cell Layer Using an Improved, Simple Apparatus for Dispersion

PURPOSE

An improved, simple apparatus was developed to easily and uniformly disperse dry powders onto an air-liquid interfaced cultured cell layer. We investigated drug permeation in cell cultures with access to the air-liquid interface (ALI) following deposition of a dry powder using the apparatus.

METHOD

The improved apparatus for dispersing the powders was assembled. Dry powders containing model drugs were prepared and dispersed onto the cell layer with ALI. After the dispersion, the permeation of each model drug was measured and compared with other samples (solutions with the same compositions).

RESULTS

The improved apparatus could with ease uniformly disperse 40% of the loading dose onto the cell layer with ALI. Dry powders showed higher drug permeability compared to the samples. without cytotoxicity or an effect on tight junctions. The high drug permeability of dry powders was independent of the molecular weight of model drugs. The contribution of active transport was small, while an increase in passive drug transport via trans- and paracellular routes was observed.

CONCLUSIONS

Inhaled dry powder formulations achieved higher drug permeability than their solution formulations in ALI. A high local concentration of drugs on the cell layer, caused by direct attachment of the inhaled dry powder, contributed to increased drug permeability via both trans- and paracellular routes.

TEER measurement techniques for in vitro barrier model systems

Transepithelial/transendothelial electrical resistance (TEER) is a widely accepted quantitative technique to measure the integrity of tight junction dynamics in cell culture models of endothelial and epithelial monolayers. TEER values are strong indicators of the integrity of the cellular barriers before they are evaluated for transport of drugs or chemicals. TEER measurements can be performed in real time without cell damage and generally are based on measuring ohmic resistance or measuring impedance across a wide spectrum of frequencies. The measurements for various cell types have been reported with commercially available measurement systems and also with custom-built microfluidic implementations. Some of the barrier models that have been widely characterized using TEER include the blood-brain barrier (BBB), gastrointestinal (GI) tract, and pulmonary models. Variations in these values can arise due to factors such as temperature, medium formulation, and passage number of cells. The aim of this article is to review the different TEER measurement techniques and analyze their strengths and weaknesses, determine the significance of TEER in drug toxicity studies, examine the various in vitro models and microfluidic organs-on-chips implementations using TEER measurements in some widely studied barrier models (BBB, GI tract, and pulmonary), and discuss the various factors that can affect TEER measurements.

Immunocompetent 3D model of human upper airway for disease modeling and in vitro drug evaluation

The development of more complex in vitro models for the assessment of novel drugs and chemicals is needed because of the limited biological relevance of animal models to humans as well as ethical considerations. Although some human-cell-based assays exist, they are usually 2D, consist of single cell type, and have limited cellular and functional representation of the native tissue. In this study, we have used biomimetic porous electrospun scaffolds to develop an immunocompetent 3D model of the human respiratory tract comprised of three key cell types present in upper airway epithelium. The three cell types, namely, epithelial cells (providing a physical barrier), fibroblasts (extracellular matrix production), and dendritic cells (immune sensing), were initially grown on individual scaffolds and then assembled into the 3D multicell tissue model. The epithelial layer was cultured at the air-liquid interface for up to four weeks, leading to formation of a functional barrier as evidenced by an increase in transepithelial electrical resistance (TEER) and tight junction formation. The response of epithelial cells to allergen exposure was monitored by quantifying changes in TEER readings and by assessment of cellular tight junctions using immunostaining. It was found that epithelial cells cocultured with fibroblasts formed a functional epithelial barrier at a quicker rate than single cultures of epithelial cells and that the recovery from allergen exposure was also more rapid. Also, our data show that dendritic cells within this model remain viable and responsive to external stimulation as evidenced by their migration within the 3D construct in response to allergen challenge. This model provides an easy to assemble and physiologically relevant 3D model of human airway epithelium that can be used for studies aiming at better understanding lung biology, the cross-talk between immune cells, and airborne allergens and pathogens as well as drug delivery.

Pharmaceutical applications of the Calu-3 lung epithelia cell line

INTRODUCTION

The Calu-3 lung cell line has been shown to be a promising in vitro model of airway epithelia due to its similarity to in vivo physiology. Hence, over the past decade, it has found increasing applications in the pharmaceutical industry.

AREAS COVERED

This review focuses on the pharmaceutical applications of the Calu-3 cell line in areas such as mechanisms of drug transport, studying aerosol deposition, controlled release studies and identification of possible drug-drug interactions. The main findings of various studies, as well as the predictive potential of this model, are presented and discussed in this review.

EXPERT OPINION

There is still a lack of mechanistic knowledge regarding transport of inhaled therapeutics across the lungs. Cell culture models such as Calu-3 provide a simple and reproducible system to study the underlying mechanisms by which inhaled therapeutics interact with the lungs. However, more complex systems that integrate particle deposition onto different cell culture systems may be useful in addressing some fundamental questions to generate a better understanding of determinants that influences pulmonary drug dissolution, absorption, metabolism and efficacy. Ultimately the use of the Calu-3 cell line provides a basic research tool that enables the development of safer and more effective inhaled therapeutics.

Pseudomonas aeruginosaInfection Destroys the Barrier Function of Lung Epithelium and Enhances Polyplex-Mediated Transfection

Challenged by the lack of success of experimental gene therapy of cystic fibrosis, we set out to investigate one of the potential causes of this failure, the barrier function of the airway epithelium and the way this is affected by bacterial infection. In an in vitro model of the airway epithelium we determined the effect of Pseudomonas aeruginosa or Escherichia coli on the transfection efficiency of polyethylenimine (PEI)-plasmid DNA complexes, carrying a luciferase gene, as well as on the barrier function of the epithelial cell layer, using transepithelial resistance (TER), cytotoxicity, bacterial transmigration, and morphological appearance as parameters. The level of luciferase expression was more than one order of magnitude higher in the cells which, before transfection, were incubated with P. aeruginosa. TER was strongly reduced by P. aeruginosa, whereas E. coli had no effect. Pseudomonas aeruginosa also effectively destroyed the structure of the tight junctions, as visualized by immunostaining of the zonula occludens. By the same token, small but significant numbers of P. aeruginosa cells were found to migrate through the epithelial layer, whereas no E. coli cells were observed at the transcompartment of the wells. Release of lactate dehydrogenase from the epithelial cells, a parameter of cell damage, occurred in a dose-dependent manner on incubation with P. aeruginosa, but not with E. coli. To evaluate the relevance of these results for the in vivo situation, we infected C57BL/6 mice with P. aeruginosa or E. coli 48 hr before transfecting them intratracheally with PEI-DNA polyplexes. Infection with P. aeruginosa caused a 5-fold increase in luciferase expression whereas infection with E. coli had no effect. Fluorescence microscopy of lung sections, after administration of fluorescein isothiocyanate-labeled polyplexes, showed that prior treatment with P. aeruginosa effectuated penetration of the complexes deeper into the epithelium than in untreated animals. In P. aeruginosa-treated animals fluorescence was detected not only in the airway epithelium itself but also in the parenchyma. We conclude that infection with P. aeruginosa causes disruption of the tight junctions between the cells and thus of the barrier function of the epithelium. As a consequence, PEI-DNA complexes injected intratracheally into infected animals gain access to the basolateral side of the cells and to spaces across the epithelial lining, giving rise to substantially increased transfection efficiency.

The addition of calcium ions to starch/Carbopol mixtures enhances the nasal bioavailability of insulin

To evaluate the influence of calcium poly(acrylates) on the nasal absorption of insulin in rabbits, starch/poly(acrylic acid) (ratio 25/75) (SD 25/75) was neutralised with NaOH and/or Ca(OH)(2). After neutralisation, a mixture of sodium and/or calcium carboxylate was formed depending on the Ca(OH)(2) concentration in the formulation. IR spectroscopy confirmed that most of the calcium molecules in the formulation interacted with acid groups of the acrylic acid polymer. Addition of Ca(OH)(2) to aqueous dispersions containing starch/poly(acrylic acid) yielded powders with an enhanced absorption of insulin after nasal delivery to rabbits in comparison with the equivalent powder without Ca(OH)(2). A mixture of SD 25/75 and Ca(OH)(2) at a ratio of 90/10 neutralised to pH 7.4 with NaOH induced the highest absorption of insulin, obtaining a bioavailability of +/-29% (vs. 19% for an equivalent formulation without Ca(OH)(2)). This increase in nasal delivery was possibly due to a higher elasticity after dispersing this formulation in nasal fluid and to a higher water absorbing capacity. Furthermore, after nasal delivery of (SD 25/75)/Ca(OH)(2) 90/10, a decrease in t(max) was observed, possibly due to a progressive dissociation of Ca(2+)-ions after hydration of the powder resulting in the closing of the tight junctions.

The control of tissue architecture over nuclear organization is crucial for epithelial cell fate

The remodeling of nuclear organization during differentiation and the dramatic alteration of nuclear organization associated with cancer development are well documented. However, the importance of tissue architecture in the control of nuclear organization remains to be determined. Differentiation of mammary epithelial cells into functional tissue structures, in three-dimensional culture, is characterized by a specific tissue architecture (i.e. a basoapical polarity axis), cell cycle exit and maintenance of cell survival. Here we show that induction of partial differentiation (i.e. basal polarity only, cell cycle exit and cell survival) by epigenetic mechanisms in malignant breast cells is sufficient to restore features of differentiation-specific nuclear organization, including perinucleolar heterochromatin, large splicing factor speckles, and distinct nuclear mitotic apparatus protein (NuMA) foci. Upon alteration of nuclear organization using an antibody against NuMA, differentiated non-neoplastic cells undergo apoptosis, whereas partially differentiated malignant cells enter the cell cycle. Non-neoplastic cells cultured under conditions that prevent the establishment of apical polarity also enter the cell cycle upon NuMA antibody treatment. These findings demonstrate that the differentiation status rather than the non-neoplastic or neoplastic origin of cells controls nuclear organization and suggest a link between nuclear organization and epigenetic mechanisms dictated by tissue architecture for the control of cell behavior.

Drug permeability in 16HBE14o- airway cell layers correlates with absorption from the isolated perfused rat lung

The permeability of the lung is critical in determining the disposition of inhaled drugs and the respiratory epithelium provides the main physical barrier to drug absorption. The 16HBE14o- human bronchial epithelial cell line has been developed recently as a model of the airway epithelium. In this study, the transport of 10 low molecular weight compounds was measured in the 16HBE14o- cell layers, with apical to basolateral (absorptive) apparent permeability coefficients (P(app)) ranging from 0.4 x 10(-6)cms(-1) for Tyr-D-Arg-Phe-Phe-NH(2) to 25.2x10(-6)cms(-1) for metoprolol. Permeability in 16HBE14o- cells was found to correlate with previously reported P(app) in Caco-2 cells and absorption rates in the isolated perfused rat lung (k(a,lung)) and the rat lung in vivo (k(a,in vivo)). Log linear relationships were established between P(app) in 16HBE14o- cells and P(app) in Caco-2 cells (r(2)=0.82), k(a,lung) (r(2)=0.78) and k(a,in vivo) (r(2)=0.68). The findings suggest that permeability in 16HBE14o- cells may be useful to predict the permeability of compounds in the lung, although no advantage of using the organ-specific cell line 16HBE14o- compared to Caco-2 cells was found in this study.

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.

Pulses of cell Ca(2+) and the dynamics of tight junction opening and closing

A mathematical modeling of tight junction (TJ) dynamics was elaborated in a previous study to better understand the dynamics of TJ opening and closing, as well as oscillations of TJ permeability that are observed in response to changes of extracellular Ca(2+) levels. In this model, TJs were assumed to be specifically controlled by the Ca(2+) concentration levels at the extracellular Ca(2+) binding sites of zonula adhaerens. Despite the fact that the model predicts all aspects of TJ dynamics, we cannot rule out the likelihood that changes of intracellular Ca(2+) concentration (Ca(2+) (cell)), which might result from changes \ of extracellular Ca(2+) concentration (Ca(2+) (extl)), contribute to the observed results. In order to address this aspect of TJ regulation, fast Ca(2+)-switch experiments were performed in which changes of Ca(2+) (cell) were induced using the Ca(2+) ionophore A23187 or thapsigargin, a specific inhibitor of the sarco-endoplasmic reticulum Ca(2+)-ATPase. The results indicate that the ionophore or thapsigargin per se do not affect basal tissue electrical conductance ( G), showing that the sealing of TJs is not affected by a rise in Ca(2+) (cell). When TJs were kept in a dynamic state, as partially open structures or in oscillation, conditions in which the junctions are very sensitive to disturbances that affect their regulation, a rise of Ca(2+) (cell) never led to a decline of G, indicating that a rise of Ca(2+) (cell) does not trigger per se TJ closure. On the contrary, always the first response to a rise of Ca(2+) (cell) is an increase of G that, in most cases, is a transient response. Despite these observations we cannot assure that a rise of Ca(2+) (cell) is without effect on the TJs, since an increase of Ca(2+) (cell) not only causes a transient increase of G but, in addition, during oscillations a rise of Ca(2+) (cell) induced by the Ca(2+) ionophore transiently halted the oscillatory pattern of TJs. The main conclusion of this study is that TJ closure that is observed when basolateral Ca(2+) concentration (Ca(2+) (bl)) is increased after TJs were opened by Ca(2+) (bl) removal cannot be ascribed to a rise of Ca(2+) (cell) and might be a consequence of Ca(2+) binding to extracellular Ca(2+) sites.

Formation and Barrier Function of Tight Junctions in Human Ovarian Surface Epithelium1

The normal ovarian surface epithelium (OSE) is a primitive epithelium made up by a single layer of mesothelial-type epithelial cells. When these cells get trapped in the ovarian stroma, expression of epithelial specific markers, such as E-cadherin, are induced. Most epithelial cells are also characterized by the ability to form tight junctions (TJ). Incomplete TJ have earlier been demonstrated in the OSE by electron microscopy studies. We have investigated expression and localization of the TJ proteins ZO-1, occludin, and claudin-1 in tissue biopsies from normal human ovaries and OSE in culture. The dynamics of TJ formation were studied in human OSE cultured on porous filters in culture inserts by measuring trans epithelial resistance (TER) including Ca(2+) switch experiments. Confluent OSE cells were also analyzed by electron microscopy. The results show that normal human OSE has expression of all three TJ proteins investigated. These proteins, ZO-1, occludin, and claudin-1, were localized to OSE cell borders both in ovarian biopsies and in cultured OSE. There was no difference in this regard between fertile and postmenopausal women. Cells in culture were polarized and presented junctional complexes seen by electron microscopy. In the Ca(2+) switch experiments, removing free Ca(2+) transiently, TER decreased significantly (P < 0.05) in the Ca(2+)-free group compared with nontreated OSE. TER was fully restored after 24 h. N-cadherin but not E-cadherin was expressed in the OSE and localized to the cell borders. We conclude that normal human OSE express and form functional TJ both in vivo and vitro. This report also describes a method to study the influence of ovarian-derived mediators on TJ in cultured OSE.

The human bronchial epithelial cell line 16HBE14o- as a model system of the airways for studying drug transport

The 16HBE14o- cell line, which forms polarised cell layers in vitro, provides a promising opportunity to develop a convenient epithelial cell culture model in which respiratory drug transport can be evaluated in vitro. This study investigated the effect of cell seeding density, collagen substratum and time in culture on the development of barrier properties in this cell line, after which the permeability of the 16HBE14o- cell layers to a series of solutes was studied. Seeding cells at a density of 2.5 x 10(5) cells per cm(2) on a monofibrillar Vitrogen-100 collagen substratum, followed by culture at an air-liquid interface for 6 days resulted in cell layers with a transepithelial electrical resistance (TER) of 247+/-47 omegacm(2) and an apparent permeability coefficient of 2.5 x 10(-6)cms(-1) for mannitol. The permeability of the 16HBE14o- cells to hydrophilic molecules (logP<1.9) was of an order of magnitude greater than that of typical alveolar cell cultures, possibly reflecting barrier properties more representative of the airways. More lipophilic drugs showed higher permeabilities indicating a sigmoidal relationship between permeability and lipophilicity similar to that observed for solute transport across primary cultured epithelial cell layers. These results indicate that under appropriate culture conditions, 16HBE14o- cell layers provide a discriminatory barrier to solute transport.

Effects of the cationic protein poly-L-arginine on airway epithelial cells in vitro

BACKGROUND

Allergic asthma is associated with an increased number of eosinophils in the airway wall. Eosinophils secrete cationic proteins, particularly major basic protein (MBP).

AIM

To investigate the effect of synthetic cationic polypeptides such as poly-L-arginine, which can mimic the effect of MBP, on airway epithelial cells.

METHODS

Cultured airway epithelial cells were exposed to poly-L-arginine, and effects were determined by light and electron microscopy.

RESULTS

Poly-L-arginine induced apoptosis and necrosis. Transmission electron microscopy showed mitochondrial damage and changes in the nucleus. The tight junctions were damaged, as evidenced by penetration of lanthanum. Scanning electron microscopy showed a damaged cell membrane with many pores. Microanalysis showed a significant decrease in the cellular content of magnesium, phosphorus, sodium, potassium and chlorine, and an increase in calcium. Plakoglobin immunoreactivity in the cell membrane was decreased, indicating a decrease in the number of desmosomes

CONCLUSIONS

The results point to poly-L-arginine induced membrane damage, resulting in increased permeability, loss of cell-cell contacts and generalized cell damage.

A study of mechanisms underlying amitriptyline-induced acute lung function impairment

In this study possible mechanisms underlying the vaso- and bronchoconstriction caused by the tricyclic antidepressant drug amitriptyline in isolated rat lungs were investigated. Some features here are similar to those apparent in adult respiratory distress syndrome and acute lung injury. Amitriptyline exposure (50 and 100 microM) caused a dose-related, pronounced, and rapid vaso- (50 microM, 30 min, p < 0.001 and 100 microM, 30 min, p < 0.001) and bronchoconstriction (50 microM, 30 min, p = 0.01 and 100 microM, 30 min, p < 0.001). The maximal noted decrease in perfusion flow was 28 +/- 2.9% at 25 min and 80 +/- 4.5% at 30 min for 50 and 100 microM amitriptyline, respectively. The maximal noted decrease in airway conductance was 29 +/- 4.7% at 25 min and 68 +/- 5.0% at 30 min. To investigate mechanisms thought to be involved in amitriptyline-induced lung function impairment, lungs were treated with several different substances including antiinflammatory agents, antioxidants, inhibitors of enzymes involved in the arachidonic acid cascade, physiological antagonists, and neurogenic antagonists. A significant reduction of amitriptyline-induced vasoconstriction was observed when lungs were treated with the protein kinase inhibitor staurosporine (3 microM, 30 min, p < 0.001), the NO-donor S-nitrosoglutathione (100 microM, 30 min, p < 0.001) and the combined endothelin A/endothelin B receptor antagonist PD 145065. This latter inhibitor caused a significant attenuation of late vasoconstriction (1 microM, 60 min, p = 0.03). The amitriptyline-induced bronchoconstriction was attenuated by the beta(2)-agonist salbutamol (1 microM, 30 min, p = 0.03) and the platelet-activating factor antagonist WEB2086 (10 microM, 30 min, p = 0.03). Staurosporine had an initial protective effect on bronchoconstriction (3 microM, 5 min, p = 0.003), while PD145065 significantly decreased bronchoconstriction 60 min after start of amitriptyline exposure (1 microM, 30 min, p = 0.003). This indicates that endothelin as well as platelet activating factor and protein kinase activation are important in mediating amitriptyline-induced lung function impairment in our experimental model and perhaps also in acute lung injury.

Effect of in vitro and in vivo aerosolized treatment with geniposide on tracheal permeability in ovalbumin-induced guinea pigs

The primary objective of this study was to investigate the effect of geniposide, a potent anti-inflammatory, on ovalbumin-antigen-induced tracheal permeability and transepithelial electrical resistance in guinea pigs. Two weeks after sensitization with ovalbumin (100 mg/ml), the permeability of guinea-pig tracheas was evaluated by flux measurements using the transcellular tracer, [(14)C]estradiol, and the paracellular tracer, [(14)C]mannitol. The effect of extracellular Ca(2+) with geniposide was also studied, using deletion of Ca(2+) in the donor chamber. The in vivo treatment effect of aerosolized geniposide on tracheal permeability in the ovalbumin-sensitized guinea pigs was also evaluated. The results indicate that tight junction permeability of ovalbumin-sensitized trachea was significantly dose dependent and decreased by geniposide (1-10 mM), as evidenced by substantial recovery of transepithelial electrical resistance and decreased transepithelial permeability of [(14)C]mannitol at (1.32+/-0.12) x 10(-5) cm/s. The effect of combination of the removal of extracellular Ca(2+) with geniposide had no effect on tight junction permeability of ovalbumin-sensitized trachea and revealed that transepithelial electrical resistance and junction permeability did not recover. In addition, the cAMP levels and phosphodiesterase activity were not significantly influenced in ovalbumin-sensitized tracheal tissues after geniposide treatment. Inhaled geniposide (50 mM, 30 min after ovalbumin sensitization) significantly restored junction permeability induced by ovalbumin (100 mg/ml, 2 min). Junction permeability did not recover on pretreatment with geniposide (50 mM for 30 min over 16 days consecutive before ovalbumin sensitization) after exposure of conscious guinea pigs to aerosol ovalbumin. In conclusion, geniposide has inhibitory effects on ovalbumin-induced junction permeability and recovery of transepithelial electrical resistance in guinea pig trachea, showing its potential as anti-asthma therapy.

Transient disruption of intercellular junctions enables baculovirus entry into nondividing hepatocytes

Baculovirus infection has extended the capabilities for transfection of exogenous genes into a variety of mammalian cell types. Because rat hepatocytes plated on collagen-coated dishes and maintained in dimethyl sulfoxide (DMSO)-supplemented chemically defined medium are an excellent model system for studying liver function in vitro, we investigated the ability of baculoviruses to infect and deliver exogenous genes to cells in this culture system. Efficient delivery to hepatocytes in short-term culture becomes restricted to peripheral cells, or "edge" cells, as the hepatocytes acquire intercellular junctions and form islands with time in culture. This barrier to baculovirus entry can be overcome, and the percentage of internal cells within the hepatocyte islands that are infected with the baculovirus can be increased more than 100-fold, when cells are subjected to transient calcium depletion before and during infection. These findings suggest that at least in some cell types, such as hepatocytes, baculovirus entry may require contact with the basolateral surface. We conclude from this study that recombinant baculovirus infection following transient depletion of extracellular calcium results in delivery of exogenous genes to at least 75% of hepatocytes in long-term DMSO culture, thereby making it possible for the first time to carry out gain-of-function and loss-of-function studies in this cell system.

EGTA enhancement of adenovirus-mediated gene transfer to mouse tracheal epithelium in vivo

Administration of recombinant adenoviral (AdV) vectors to animals can lead to inflammatory and immune responses. For therapeutic indications in which repeated treatment is necessary, such as cystic fibrosis (CF), these responses can limit the therapeutic usefulness of the vector. In principle, the utility of the vector can be improved by increasing its therapeutic index, that is, by either increasing its efficacy or decreasing its toxicity. A strategy that would enhance the efficacy of an adenoviral approach would allow the use of fewer virus particles to achieve a given level of transgene expression, and thereby also reduce unwanted effects such as immune responses. Following up on our observation that treating polarized normal human bronchial epithelial cells with calcium (Ca(2+))-free medium or the calcium chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) significantly enhanced the subsequent transfection of these cells with cationic lipid:pDNA complexes, we have now asked whether such a treatment protocol might also improve the ability of AdV to infect these cells. Treating polarized airway epithelial cells with EGTA led to a dramatic increase in AdV-mediated transduction, as demonstrated by an approximately 50-fold increase in transgene expression. This strategy was also tested in vivo and resulted in substantial increases (up to 50-fold) in the ability of AdV vectors to infect mouse tracheal epithelium. Transfection of mouse trachea with an AdV aerosol was also significantly increased by pretreatment with EGTA. The enhancing effects of EGTA could not be duplicated with hypo- or hyperosmotic treatments. Light microscopy of mouse trachea that had been EGTA treated and then infected with AdV demonstrated an EGTA-mediated AdV infection of airway epithelial cells. The apparent enhanced potency of AdV for airway cells resulting from this strategy provides a significant increase in the therapeutic index of this gene delivery vector, and may increase the likelihood that it can be used for clinical indications requiring chronic administration of the vector.

Inducible expression of Enterococcus faecalis aggregation substance surface protein facilitates bacterial internalization by cultured enterocytes

Aggregation substance (AS) is an Enterococcus faecalis surface protein that may contribute to virulence. Using a recently described system for controlled expression of AS in E. faecalis and the heterologous host Lactococcus lactis, experiments were designed to assess the effect of AS on bacterial internalization by HT-29 and Caco-2 enterocytes. AS expression was associated with increased internalization of E. faecalis by HT-29 enterocytes and of L. lactis by HT-29 and Caco-2 enterocytes. Compared to enterocytes cultivated under standard conditions, either cultivation in hypoxia or 1-h pretreatment of enterocytes with calcium-free medium resulted in increased internalization of both E. faecalis and L. lactis (with and without AS expression). Also, AS expression augmented these increases when E. faecalis was incubated with pretreated HT-29 enterocytes and when L. lactis was incubated with pretreated Caco-2 and HT-29 enterocytes. These data indicated that AS might facilitate E. faecalis internalization by cultured enterocytes.

Increasing epithelial junction permeability enhances gene transfer to airway epithelia In vivo

Gene transfer to airway epithelia is the most direct approach for treating the progressive lung disease associated with cystic fibrosis. However, the transduction efficiency is poor when viral vectors are applied to the mucosal surface. We reported previously that gene transfer via the apical surface of human airway epithelia in vitro was improved by formulating vectors with ethyleneglycol-bis-(2-aminoethyl ether)- N,N,N',N'-tetraacetic acid (EGTA) in a hypotonic buffer. First, we investigated the mechanism for this enhancement. When 100-nm fluorescent beads were applied to the apical surface in the presence of EGTA, paracellular deposition of the particles was noted. Transmission electron microscopy verified that the epithelial junction complex was disrupted under these conditions. The Ca(2+) chelators EGTA, 1,2-bis (2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), and ethylenediaminetetraacetic acid all caused a rapid, reversible drop in transepithelial resistance and facilitated gene transfer with retrovirus or adenovirus in vitro. When Ca(2+) chelators were applied to rabbit tracheal epithelia or human nasal epithelia in vivo, the transepithelial voltage decreased, and amiloride sensitivity was lost, suggesting that epithelial junctions opened. Importantly, this novel formulation enhanced both retroviral- and adenoviral-mediated gene transfer to rabbit tracheal epithelia in vivo. This technique may have applications for vector or drug delivery to airway epithelia and other polarized cells.

Amitriptyline-induced loss of tight junction integrity in a human endothelial--smooth muscle cell bi-layer model

Tricyclic antidepressants can, when taken in overdose, cause serious pulmonary failure such as the adult respiratory distress syndrome (ARDS). In this study we have examined the effects of some tricyclic antidepressants (amitriptyline, imipramine, nortriptyline and desipramine) on the viability and morphology of human endothelial and smooth muscle cells derived from umbilical cord. Effects of amitriptyline on endothelial cell fluidity, as well as permeability changes to an endothelial-smooth muscle cell bi-layer, were also studied. The tricyclic antidepressants induced acute, sub-lethal toxicity in both cell types above 100 microM as assessed by the MTT reduction assay. Morphological changes were also observed at these concentrations. Such changes were, however, absent at 33 microM and below. Amitriptyline did, however, cause a concentration-dependent fall in the electrical resistance of an endothelial-smooth muscle cell bi-layer, with significant effects already evident at 33 microM. All of these observed effects were fairly rapid and appeared within 5-15 min of exposure. The rapidity of these permeabilisation effects suggests potential membrane perturbations, since tricyclic antidepressants are lipophilic molecules with affinity for cell membranes. However, fluorescence anisotropy measurements showed no significant difference in membrane fluidity between amitriptyline-treated and control endothelial cells. Collectively, these data point to specific mechanisms of action of amitriptyline, and probably also the other tricyclic antidepressants studied, on endothelial permeability, which is a hallmark of ARDS. The data suggest that increased endothelial permeability could be due to impaired tight junction function.

Basolateral localization of fiber receptors limits adenovirus infection from the apical surface of airway epithelia

Recent identification of two receptors for the adenovirus fiber protein, coxsackie B and adenovirus type 2 and 5 receptor (CAR), and the major histocompatibility complex (MHC) Class I alpha-2 domain allows the molecular basis of adenoviral infection to be investigated. Earlier work has shown that human airway epithelia are resistant to infection by adenovirus. Therefore, we examined the expression and localization of CAR and MHC Class I in an in vitro model of well differentiated, ciliated human airway epithelia. We found that airway epithelia express CAR and MHC Class I. However, neither receptor was present in the apical membrane; instead, both were polarized to the basolateral membrane. These findings explain the relative resistance to adenovirus infection from the apical surface. In contrast, when the virus was applied to the basolateral surface, gene transfer was much more efficient because of an interaction of adenovirus fiber with its receptors. In addition, when the integrity of the tight junctions was transiently disrupted, apically applied adenovirus gained access to the basolateral surface and enhanced gene transfer. These data suggest that the receptors required for efficient infection are not available on the apical surface, and interventions that allow access to the basolateral space where fiber receptors are located increase gene transfer efficiency.

The extra- and intracellular barriers to lipid and adenovirus-mediated pulmonary gene transfer in native sheep airway epithelium

Gene transfer to the respiratory epithelium is currently suboptimal and may be helped by the identification of limiting biological barriers. We have, therefore, developed an ex vivo model which retains many of the characteristics of in vivo native airways including mucociliary clearance, mucus coverage and an intact cellular structure. Using this model we have demonstrated several barriers to gene transfer. Liposome-mediated gene transfer was inhibited by normal mucus, with removal of this layer increasing expression approximately 25-fold. In addition both liposome and adenovirus were inhibited by CF sputum. The apical membrane represented a significant barrier to both agents. Adenovirus-mediated expression could be significantly augmented by increasing contact time or by pre-treatment of tissues with a nominally calcium-free medium. The presence of these extracellular and plasma membrane barriers appeared to be the key parameters responsible for the approximately three log difference in gene expression found in vitro compared with our ex vivo model. Cytoskeletal elements and the cell cycle also influenced in vitro gene transfer, and represent further barriers which need to be overcome.

Binding and uptake of cationic lipid:pDNA complexes by polarized airway epithelial cells

To better understand the barriers associated with cationic lipid-mediated gene transfer to polarized epithelial cells, Fischer rat thyroid (FRT) cells and polarized normal human bronchial epithelial (NHBE) cells grown on filter supports at an air-liquid interface were used to study the binding and uptake of cationic lipid:plasmid DNA (pDNA) complexes. The efficiencies of binding and uptake of cationic lipid:pDNA complexes by these cell systems were monitored using fluorescence microscopy of fluorescently tagged lipid or pDNA probes. Fluorescent probe bound to the cell surface was differentiated from internalized probe by adding trypan blue, which quenched the fluorescence of bound but not internalized probes. For proliferating cells, binding and internalization of the cationic lipid:pDNA complexes were determined to be efficient. In contrast, little binding or internalization of the complexes was observed using polarized epithelial cells. However, after aspirating a small area of cells from the filter support, virtually all of the cells adjoining this newly formed edge bound and internalized the cationic lipid:pDNA complexes. To determine if their uptake in edge cells was related to the ability of the complexes to access the basolateral membranes of these cells, the binding and uptake of complexes was monitored in polarized NHBE cells that had been pretreated with EGTA or Ca2+-free media, strategies known to disrupt tight junctions. Cells treated in this manner bound and internalized cationic lipid:pDNA complexes efficiently and also expressed significant levels of transgene product. Control cells with intact tight junctions neither bound complexes nor expressed significant transgene product. These data confirm and extend earlier observations that the polarized apical membranes of airway epithelial cells are resistant to transfection by lipid:pDNA complexes. Further, in contrast to previous studies that have shown the entry step of complexes is not an important barrier for COS and HeLa cells, binding and entry of complexes in polarized NHBE cells appear to be rate limiting. These findings suggest that strategies designed to open the tight junctions of polarized epithelial cells may improve gene delivery to these cells for diseases such as cystic fibrosis (CF).

Polarity influences the efficiency of recombinant adenoassociated virus infection in differentiated airway epithelia

To better understand mechanisms that limit rAAV transduction in the lung, we have evaluated several unique features of rAAV infection in polarized primary airway epithelial cultures. rAAV was found to transduce the basolateral surface of airway epithelia 200-fold more efficiently than the apical membrane. These differences in membrane infection correlated with the abundance of apical heparan sulfate proteoglycan (AAV-2 receptor) and virus binding. UV irradiation augmented rAAV transduction greater than 20-fold, only when virus was applied to the apical membrane. Ultrastructural analysis of UV-irradiated primary cultures demonstrated significant changes in microvilli architecture following exposure to 25 J/m2 UV. Although virus binding and the abundance of heparan sulfate proteoglycan were not increased at the apical membrane following UV irradiation, increased receptor-independent endocytosis of fluorescent beads was seen at the apical membrane following UV irradiation. We hypothesize that endocytotic processes associated with apical membrane-specific pathways of viral entry, and/or processing of virus to the nucleus, may be altered following UV irradiation. Interestingly, UV irradiation had an inhibitory effect on rAAV transduction from the basolateral membrane, which correlated with a decrease in the abundance of heparan sulfate proteoglycan at the basal membrane. In summary, these findings suggest that independent pathways of viral transduction may occur in the apical and basolateral compartments of polarized airway epithelia.

Influence of cell polarity on retrovirus-mediated gene transfer to differentiated human airway epithelia

Gene transfer with recombinant murine leukemia viruses (MuLV) provides the potential to permanently correct inherited lung diseases, such as cystic fibrosis (CF). Several problems prevent the application of MuLV-based recombinant retroviruses to lung gene therapy: (i) the lack of cell proliferation in mature pulmonary epithelia, (ii) inefficient gene transfer with a vector applied to the apical surface, and (iii) low titers of many retroviral preparations. We found that keratinocyte growth factor (KGF) stimulated proliferation of differentiated human tracheal and bronchial epithelia. Approximately 50% of epithelia divided in response to KGF as assessed by bromodeoxyuridine histochemistry. In airway epithelia stimulated to divide with KGF, high-titer ampho- and xenotropic enveloped vectors preferentially infected cells from the basal side. However, treatment with hypotonic shock or EGTA transiently increased transepithelial permeability, enhancing gene transfer with the vector applied to the mucosal surfaces of KGF-stimulated epithelia. Up to 35% of cells expressed the transgene after gene transfer. By using this approach, cells throughout the epithelial sheet, including basal cells, were targeted. Moreover, the Cl- transport defect in differentiated CF airway epithelia was corrected. These findings suggest that barriers to apical infection with MuLV can be overcome.

Cell lines of pulmonary and non-pulmonary origin as tools to study the effects of house dust mite proteinases on the regulation of epithelial permeability

BACKGROUND

Allergenic and non-allergenic proteinases from house dust mites (HDM) cause loss of adhesion between airway epithelial cells that may result in a loss of functional cohesion between the cells and thus assist in allergen presentation. Improved cellular assay systems are needed to ascertain the mechanisms involved.

OBJECTIVES

To survey a series of epithelial cell lines (Calu-3, 16HBE14o-, NCI-H292 and A549 from human airways, and MDCK from dog kidney) and establish their utility for studies of the effects of HDM proteinases from D. pteronyssinus on epithelial permeability. To develop an improved method for measuring changes in epithelial permeability induced by HDM proteinases and other provocants.

METHODS

The permeability of epithelial monolayer cultures to mannitol was calculated from measurements of clearance using a technique that permits mathematical estimation and reduction of non-cellular diffusional constraints. Permeability was studied under control conditions and after perturbation of monolayers with HDM proteinases (separated into serine- and cysteine-proteinase classes) or chelation of extracellular Ca2+. Fluorescent antibody staining was used to investigate whether the cells expressed tight junctions (staining of ZO-1), desmosomes (staining of desmoplakin) and zonulae adherentes (staining of E-cadherin).

RESULTS

The Calu-3 line was identified as an airway cell line that expressed functional tight junctions, desmosomes and zonulae adherentes. Calu-3 monolayers exhibited a low clearance and permeability to mannitol, similar to that seen in the extensively characterized MDCK cell line. Clearance and permeability were significantly increased by treatment with either HDM proteinase fraction or by calcium chelation. 16HBE14o- cells also had a low permeability to mannitol under control conditions and expressed a similar repertoire of functional proteins from major intercellular junctions. In contrast, NCI-H292 and A549 cell lines were functionally deficient in tight junctions, although they did express desmosomes and zonulae adherentes to a greater extent. Epithelial permeability was found to be a more appropriate and sensitive index of epithelial perturbation than was tracer clearance.

CONCLUSION

These results suggest that the Calu-3 and 16HBE14o- cell lines are useful tools in studying the mechanism of HDM proteinases on airway epithelial cell function. HDM proteinases of both cysteine and serine mechanistic classes were found to perturb epithelial adhesion and function.

Calcium site specificity. Early Ca2+-related tight junction events

The molecular mechanisms by which Ca2+ and metal ions interact with the binding sites that modulate the tight junctions (TJs) have not been fully described. Metal ions were used as probes of these sites in the frog urinary bladder. Basolateral Ca2+ withdrawal induces the opening of the TJs, a process that is abruptly terminated when Ca2+ is readmitted, and is followed by a complete recovery of the TJ seal. Mg2+ and Ba2+ were incapable of keeping the TJ sealed or of inducing TJ recovery. In addition, Mg2+ causes a reversible concentration-dependent inhibition of the Ca2+-induced TJ recovery. The effects of extracellular Ca2+ manipulation on the TJs apparently is not mediated by changes of cytosolic Ca2+ concentration. The transition elements, Mn2+ and Cd2+, act as Ca2+ agonists. In the absence of Ca2+, they prevent TJ opening and almost immediately halt the process of TJ opening caused by Ca2+ withdrawal. In addition, Mn2+ promotes an almost complete recovery of the TJ seal. Cd2+, in spite of stabilizing the TJs in the closed state and halting TJ opening, does not promote TJ recovery, an effect that apparently results from a superimposed toxic effect that is markedly attenuated by the presence of Ca2+. The interruption of TJ opening caused by Ca2+, Cd2+, or Mn2+, and the stability they confer to the closed TJs, might result from the interaction of these ions with E-cadherin. Addition of La3+ (2 microM) to the basolateral Ca2+-containing solution causes an increase of TJ permeability that fully reverses when La3+ is removed. This effect of La3+, observed in the presence of Ca2+ (1 mM), indicates a high La3+ affinity for the Ca2+-binding sites. This ability of La3+ to open TJs in the presence of Ca2+ is a relevant aspect that must be considered when using La3+ in the evaluation of TJ permeability of epithelial and endothelial membranes, particularly when used during in vivo perfusion or in the absence of fixatives.

Deficiency of nitric oxide in allergen-induced airway hyperreactivity to contractile agonists after the early asthmatic reaction: an ex vivo study

1. Using a guinea-pig model of allergic asthma, we investigated the role of nitric oxide (NO) in allergen-induced airway hyperreactivity after the early asthmatic reaction, by examining the effects of the NO-synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the responsiveness to methacholine and histamine of isolated perfused tracheae from unchallenged (control) animals and from animals 6 h after ovalbumin challenge. 2. All animals developed airway hyperreactivity to inhaled histamine at 6 h after ovalbumin challenge, with a mean 3.11 +/- 0.45 fold increase in sensitivity to the agonist (P < 0.001). 3. In perfused tracheal preparations from the ovalbumin-challenged guinea-pigs, the maximal responses (Emax) to methacholine and histamine were significantly enhanced compared to controls, both after intraluminal (IL) and extraluminal (EL) administration of the contractile agonists. In addition, a small but significant increase in the pD2 (-log10 EC50) for IL and EL methacholine and for IL histamine was observed. As a consequence, the delta pD2 (EL-IL) for histamine was slightly decreased from 1.67 +/- 0.13 to 1.23 +/- 0.14 (P < 0.05). However, the delta pD2 for methacholine was unchanged (1.85 +/- 0.11 and 1.77 +/- 0.12, respectively; NS). 4. Incubation of control tracheae with 100 microM L-NAME (IL) significantly enhanced the Emax for both IL and EL methacholine and histamine to approximately the same degree as observed after ovalbumin challenge, with no effect on the pD2 and delta pD2 for both agonists. On the contrary, L-NAME had no effect on Emax and pD2 values of tracheal preparations from ovalbumin-challenged guinea-pigs. 5. L-NAME (10 microM-1 mM) had no effect on methacholine-induced contraction of isolated tracheal strip preparations obtained from control animals, indicating that L-NAME has no antimuscarinic effect on tracheal smooth muscle. 6. Histological examination of the intact tracheal preparations indicated epithelial and subepithelial infiltration of eosinophils after ovalbumin challenge. However, no apparent damage of the airway epithelium was observed in these preparations. 7. The results indicate that a deficiency of NO contributes to allergen-induced airway hyperreactivity after the early asthmatic reaction and that this deficiency appears not to be due to epithelial shedding.

Alveolar permeability enhancement by oleic acid and related fatty acids: evidence for a calcium-dependent mechanism

Pulmonary exposure to oleic acid (OA) is associated with permeability alterations and cellular damage; however, the exact relationship between these two effects has not been clearly established. Using cultured alveolar epithelial monolayers, we demonstrated that OA and some other fatty acids (< or = 50 microM) can induce permeability changes without detectable cellular damage. At higher concentrations, however, OA caused severe membrane damage and leakage to solute flux. The permeability enhancing effect of OA was observed with both the paracellular marker 3H-mannitol and the lipophilic transcellular indicator 14C-progesterone. While the effect of OA on transcellular permeability may be attributed to its known effect on membrane fluidity, the paracellular promoting effect of OA and its mechanism are not well established. We postulated that OA may increase paracellular permeability through a Ca(2+)-dependent tight junction mechanism. Using dual-excitation fluorescence microscopy, we demonstrated that OA can increase intracellular calcium, [Ca2+]i, in a dose-dependent manner. This effect was transient at low OA concentrations (< or = 50 microM) but became more pronounced and sustained at higher concentrations. Free hydroxyl and unsaturated groups were required for this activation since esterified OA (oleic methyl ester) and stearic acid (a saturated fatty acid with equal chain length) had much reduced effects on both the [Ca2+]i and the permeability alterations. Degree of unsaturation was unimportant since linolenic acid (18:3), linoleic acid (18:2), and OA (18:1) had similar and comparable effects on the two parameters.(ABSTRACT TRUNCATED AT 250 WORDS)