Molecular structure of the apical junction complex and its contribution to the paracellular barrier

Emerging investigator series: the role of chemical properties in human exposure to environmental chemicals

One of the ultimate goals of environmental exposure science is to mechanistically understand how chemical properties and human behavior interactively determine human exposure to the wide spectrum of chemicals present in the environment. This comprehensive review assembles state-of-the-art knowledge of the role of partitioning, dissociation, mass transfer, and reactive properties in human contact with and absorption of organic chemicals via oral, dermal, and respiratory routes. Existing studies have revealed that chemicals with different properties vary greatly in mass distribution and occurrence among multiple exposure media, resulting in distinct patterns of human intake from the environment. On the other hand, these chemicals encounter different levels of resistance in the passage of intestinal, dermal, and pulmonary absorption barriers and demonstrate different levels of bioavailability, due to the selectivity of biochemical, anatomical and physiological structures of these absorption barriers. Moving forward, the research community needs to gain more in-depth mechanistic insights into the complex processes in human exposure, advance the technique to better characterize and predict chemical properties, generate and leverage experimental data for a more diverse range of chemicals, and describe better the interactions between chemical properties and human behavior.

Mycotoxin Deoxynivalenol Has Different Impacts on Intestinal Barrier and Stem Cells by Its Route of Exposure

The different effects of deoxynivalenol (DON) on intestinal barrier and stem cells by its route of exposure remain less known. We explored the toxic effects of DON on intestinal barrier functions and stem cells after DON microinjection (luminal exposure) or addition to a culture medium (basolateral exposure) using three-dimensional mouse intestinal organoids (enteroids). The influx test using fluorescein-labeled dextran showed that basolateral DON exposure (1 micromolar (µM) disrupted intestinal barrier functions in enteroids compared with luminal DON exposure at the same concentration. Moreover, an immunofluorescence experiment of intestinal epithelial proteins, such as E-cadherin, claudin, zonula occludens-1 (ZO-1), and occludin, exhibited that only basolateral DON exposure broke down intestinal epithelial integrity. A time-lapse analysis using enteroids from leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5)-enhanced green fluorescence protein (EGFP) transgenic mice and 5-ethynyl-2-deoxyuridine (EdU) assay indicated that only the basolateral DON exposure, but not luminal DON exposure, suppressed Lgr5⁺ stem cell count and proliferative cell ratio, respectively. These results revealed that basolateral DON exposure has larger impacts on intestinal barrier function and stem cells than luminal DON exposure. This is the first report that DON had different impacts on intestinal stem cells depending on the administration route. In addition, RNA sequencing analysis showed different expression of genes among enteroids after basolateral and luminal DON exposure.

Molecular Docking of Interaction between E-Cadherin Protein and Conformational Structure of Cyclic Peptide ADTC3 (Ac-CADTPC-NH2) Simulated on 20 ns

Pengobatan penyakit yang menyerang otak sangat sulit dilakukan karena penghantaran molekul obat menuju otak terhalang oleh molekul-molekul blood-brain barrier (BBB). Untuk mengatasinya telah dikembangkan metode baru dengan memodulasi junction antar sel menggunakan peptida. Salah satu peptida yang diperkirakan mampu memodulasi adalah ADTC3, yang diturunkan dari susunan asam amino kadherin. Modulasi terjadi diduga karena interaksi antara ADTC3 dengan E-kadherin. Pada penelitian ini telah dihitung energi interaksi antara ADTC3 dengan E-kadherin. Metode yang digunakan adalah dinamika molekul (DM) dan molecular docking. Hasil penelitian menunjukkan bahwa peptida siklik ADTC3 (Ac-CADTPC-NH2) hasil simulasi 20 ns (20.000 ns) berinteraksi kuat dengan domain EC1 E-kadherin dengan energy binding sebesar -31,55 kJ.mol-1 dan tetapan inhibisi Ki sebesar 2,96 µM pada konformasi ke-4487. Interaksi yang kuat ini diperkirakan sebagai daya penggerak memodulasi junction antar sel. Interaksi antara ADTC3 dengan E-kadherin terjadi pada situs residu E-kadherin Asp1, Trp2, Val3, Ile4, Lys25, Met92 yang berada pada daerah adhesion arm-acceptor pocket.

Peptides and Drug Delivery

Peptides have been used as drugs to treat various health conditions, and they are also being developed as diagnostic agents. Due to their receptor selectivity, peptides have recently been utilized for drug delivery to target drug molecules to specific types of cells (i.e. cancer cells, immune cells) to lower the side effects of the drugs. In this case, the drug is conjugated to the carrier peptide for directing the drug to the target cells (e.g. cancer cells) with higher expression of a specific receptor that recognizes the carrier peptide. As a result, the drug is directed to the target diseased cells without affecting the normal cells. Peptides are also being developed for improving drug delivery through the intestinal mucosa barrier (IMB) and the blood-brain barrier (BBB). These peptides were derived from intercellular junction proteins such as occludins, claudins, and cadherins and improve drug delivery through the IMB and BBB via the paracellular pathways. It is hypothesized that the peptides modulate protein-protein interactions in the intercellular junctions of the IMB and BBB to increase the porosity of paracellular pathways of the barriers. These modulator peptides have been shown to enhance brain delivery of small molecules and medium-sized peptides as well as a large protein such as 65 kDa albumin. In the future, this method has the potential to improve oral and brain delivery of therapeutic and diagnostic peptides and proteins.

Interferon-gamma increased epithelial barrier function via upregulating claudin-7 expression in human submandibular gland duct epithelium

Tight junctions (TJs) are necessary for salivary gland function and may serve as indicators of salivary gland epithelial dysfunction. IgG4-related disease (IgG4-RD) is a newly recognized fibro-inflammatory condition which disrupts the TJ associated epithelial barrier. The salivary glands are one of the most frequently involved organs in IgG4-RD, however, changes of the TJ associated epithelial barrier in salivary gland duct epithelium is poorly understood. Here, we investigated the regulation and function of TJs in human submandibular gland ductal epithelial cells (HSDECs) in normal and IgG4-RD. We examined submandibular gland (SMG) tissue from eight control individuals and 22 patients with IgG4-RD and established an HSDEC culture system. Immunohistochemistry, immunocytochemistry, western blotting, and measurement of transepithelial electrical resistance (TER) were performed. Claudin-4, claudin-7, occludin, and JAM-A were expressed at the apical side of the duct epithelium in submandibular gland (SMG) tissue and at the cell borders in HSDECs of normal and IgG4-RD. The expression and distribution of TJs in SMG tissue were not different in control individuals and patients with IgG4-RD in vivo and in vitro. Although interferon-gamma (IFNγ) generally disrupts the integrity and function of TJs, as manifested by decreased epithelial barrier function, IFNγ markedly increased the epithelial barrier function of HSDECs via upregulation of claudin-7 expression in HSDECs from patients with IgG4-RD. This is the first report showing an IFNγ-dependent increase in epithelial barrier function in the salivary gland duct epithelium. Our results provide insights into the functional significance of TJs in salivary gland duct epithelium in physiological and pathological conditions, including IgG4-RD.

The adherens junction is lost during normal pregnancy but not during ovarian hyperstimulated pregnancy

During early pregnancy in the rat, the luminal uterine epithelial cells (UECs) must transform to a receptive state to permit blastocyst attachment and implantation. The implantation process involves penetration of the epithelial barrier, so it is expected that the transformation of UECs includes alterations in the lateral junctional complex. Previous studies have demonstrated a deepening of the tight junction (zonula occludens) and a reduction in the number of desmosomes (macula adherens) in UECs at the time of implantation. However, the adherens junction (zonula adherens), which is primarily responsible for cell-cell adhesion, has been little studied during early pregnancy. This study investigated the adherens junction in rat UECs during the early stages of normal pregnancy and ovarian hyperstimulated (OH) pregnancy using transmission electron microscopy. The adherens junction is present in UECs at the time of fertilisation, but is lost at the time of blastocyst implantation during normal pregnancy. Interestingly, at the time of implantation after OH, adherens junctions are retained and may impede blastocyst penetration of the epithelium. The adherens junction anchors the actin-based terminal web, which is known to be disrupted in UECs during early pregnancy. However, artificial disruption of the terminal web, using cytochalasin D, did not cause removal of the adherens junction in UECs. This study revealed that adherens junction disassembly occurs during early pregnancy, but that this process does not occur during OH pregnancy. Such disassembly does not appear to depend on the disruption of the terminal web.

Lipid polymer hybrid as emerging tool in nanocarriers for oral drug delivery

The oral route for drug delivery is a widely accepted route. For that reason, many researchers are currently working to develop efficient oral drug delivery systems. Use of polymeric nanoparticles (NPs) and lipid carrier systems, including liposomes, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLC), has limitations such as drug leakage and high water content of dispersions. Thus, lipid polymer hybrid nanoparticles (LPNs) have been explored by the researchers to provide a better effect using properties of both polymers and lipids. The present review is focused on the challenges, possibilities, and future perspectives of LPNs for oral delivery.

Deoxynivalenol: a trigger for intestinal integrity breakdown

Disintegration of the colonic epithelial barrier is considered a key event in the initiation and progression of inflammatory bowel and celiac disease. As the primary etiology of these diseases remains unknown, we hypothesized that the trichothecene deoxynivalenol (DON), a fungal metabolite found in grain-based human diets, might be one of the triggers resulting in an impairment of the intestinal tight junction network preceding an inflammatory response. Using horizontal impedance measurements, we demonstrate that DON disintegrates a human Caco-2 cell monolayer within <1 h after exposure to concentrations as low as 1.39 μM. This initial trigger is followed by a decrease in transepithelial resistance and an increased permeability of marker molecules, such as lucifer yellow and FITC-labeled dextran. In parallel, the increase in paracellular transport of FITC-dextran is demonstrated in vivo in B6C3F1 mice, challenged orally with DON. In vitro claudin protein levels are decreased and correlated with a displacement within the cells in vitro and in vivo, accompanied by a compensatory up-regulation of mRNA levels of claudins and their binding partner ZO-1. In treated mice, alterations in villus architecture in the entire intestinal tract resemble the disintegration of the epithelial barrier, a characteristic of chronic inflammatory bowel disease.

Enhancement of drug absorption through the blood-brain barrier and inhibition of intercellular tight junction resealing by E-cadherin peptides

E-cadherin-mediated cell-cell interactions in the zonula adherens play an important role in the formation of the intercellular tight junctions found in the blood-brain barrier. However, it is also responsible for the low permeation of drugs into the brain. In this study, HAV6 peptide derived from the EC1 domain of E-cadherin was found to enhance the permeation of ¹⁴C-mannitol and [³H(G)]-daunomycin through the blood-brain barrier of the in situ rat brain perfusion model. In addition, HAV6 peptide and verapamil have a synergistic effect in enhancing the BBB permeation of daunomycin. A new intercellular-junction resealing assay was also developed using Caco-2 monolayers to evaluate new peptides (BLG2, BLG3, and BLG4) derived from the bulge regions of the EC2, EC3, and EC4 domains of E-cadherin. BLG2 and BLG4 peptides but not BLG3 peptides were found to be effective in blocking the resealing of the intercellular junctions. The positive control peptides (ADT10, ADT6, and HAV10) block the resealing of the intercellular junctions in a concentration-dependent manner. All these findings suggest that E-cadherin-derived peptides can block E-cadherin-mediated cell-cell interactions. These findings demonstrate that cadherin peptides may offer a useful targeted permeation enhancement of therapeutic agents such as anticancer drugs into the brain.

Tight junctions in salivary epithelium

Epithelial cell tight junctions (TJs) consist of a narrow belt-like structure in the apical region of the lateral plasma membrane that circumferentially binds each cell to its neighbor. TJs are found in tissues that are involved in polarized secretions, absorption functions, and maintaining barriers between blood and interstitial fluids. The morphology, permeability, and ion selectivity of TJ vary among different types of tissues and species. TJs are very dynamic structures that assemble, grow, reorganize, and disassemble during physiological or pathological events. Several studies have indicated the active role of TJ in intestinal, renal, and airway epithelial function; however, the functional significance of TJ in salivary gland epithelium is poorly understood. Interactions between different combinations of the TJ family (each with their own unique regulatory proteins) define tissue specificity and functions during physiopathological processes; however, these interaction patterns have not been studied in salivary glands. The purpose of this review is to analyze some of the current data regarding the regulatory components of the TJ that could potentially affect cellular functions of the salivary epithelium.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

Oral delivery of low-molecular-weight heparin using sodium caprate as absorption enhancer reaches therapeutic levels

The primary objective of this study was to evaluate sodium caprate as an oral penetration enhancer for low molecular weight heparin (LMWH), ardeparin. In vitro studies using Caco-2 cell monolayer indicated that 0.0625% of sodium caprate gave approximately 2-fold enhancement of ardeparin compared to negative control with almost 100% cell survival as evaluated by MTT cytotoxicity assay. In vivo studies in rats with ardeparin (1,200 IU/kg) and sodium caprate (100 mg/kg) led to a relative bioavailability of 27% with plasma anti-factor Xa levels within the therapeutic range (>0.2 IU/ml). Moreover, under these conditions, histological examination provided evidence that there was no damage to the gastrointestinal wall. Regional permeability studies using rat intestine indicated the colon as the region of maximum permeation. These results suggest that, at the dose administered, sodium caprate acts as a relatively safe and efficient absorption enhancer in the quest for alternatives for the oral delivery of LMWH.

Epithelial barrier characteristics and expression of cell adhesion molecules in proximal tubule-derived cell lines commonly used for in vitro toxicity studies

Recent studies indicate that the actions of several nephrotoxic substances involve alterations in the function of cell adhesion molecules and changes in the paracellular permeability of the proximal tubule. In light of these findings, there is a need for appropriate in vitro model systems to study these phenomenae in greater detail. In the present study, the transepithelial resistance (TER), paracellular permeability of 14C-mannitol and immunofluorescent labeling of cell adhesion molecules (E-cadherin, N-cadherin, ZO-1, occludin, and claudins-2 and -7) were evaluated in several proximal tubule-derived cell lines that have been commonly used as model systems for in vitro toxicity studies. The cell lines studied included: LLC-PK1, OK, NRK-52E and HK-2, along with commercially available primary cultures of human renal proximal tubule epithelial cells (HRPTE). LLC-PK1 cells developed the highest TER followed by the OK cells and NRK-52E cells. The other cell lines failed to develop a TER even after 2 weeks in culture. There was a direct correlation between TER and ability to restrict paracellular movement of 14C-mannitol. Labeling studies showed that the LLC-PK1 and NRK-52E cells expressed high levels of E-cadherin while the HRPTE cells expressed lower levels. OK cells expressed moderate levels of N-cadherin while LLC-PK1 and NRK-52E cells expressed lower levels in isolated patches of cells. All cell lines expressed moderate-high levels of ZO-1. LLC-PK1 also expressed the tight-junction proteins occludin and claudin-7; OK cells also expressed moderate levels of occludin. All other cell lines had weak claudin-7 and occludin labeling. None of the cell lines expressed claudin-2. These results show that the LLC-PK1, OK and NRK-52E cell lines exhibit characteristics that most closely resembled those of the proximal tubule in vivo, and they indicate that these cell lines would be appropriate models for studying the effects of toxicants on cell-cell junctions and cell adhesion molecules.

Enhancement of brain distribution of anticancer agents using ΔG, the 12kDa active fragment of ZOT

OBJECTIVE

The objective of this study was to evaluate the ability of DeltaG, the 12 kDa active fragment of ZOT, to increase the brain distribution of MTX and paclitaxel, two commonly used anticancer agents with poor distribution into the brain.

METHODS

As part of dose estimation of DeltaG, [14C]-sucrose (40 microCi/kg), a hydrophilic paracellular marker, was co-administered with DeltaG (0, 400 and 800 microg/kg) with and without protease inhibitors to male Sprague-Dawley rats (n=3 per group) via an intracarotid cannula. MTX (50 mg/kg) and [3H]-paclitaxel (120 microCi/kg) were co-administered with the effective doses of DeltaG determined from the above study via the intracarotid cannula. Animals were euthanized by carbon dioxide asphyxiation at the specified time periods and brain and plasma samples were analyzed for the respective drug.

RESULTS

The brain distribution of [14C]-sucrose was significantly enhanced at both doses of DeltaG. A fold enhancement in the B/P ratios of 1.88 and 2.68 was observed at the 400 and 800 microg/kg doses respectively, when the protein was protected from metabolic degradation with PIs. DeltaG significantly increased the brain distribution of MTX at each of the doses administered, with over a seven-fold increase at the 600 microg/kg dose. [3H]-paclitaxel brain AUC(0-60 min) was significantly higher in the presence of DeltaG (800 microg/kg with PIs) with a 2.5-fold enhancement in brain exposure.

CONCLUSIONS

DeltaG significantly enhances the brain distribution of MTX (hydrophilic) and paclitaxel (lipophilic) and has the potential to be further developed as adjunct therapy to increase delivery of poorly permeable chemotherapeutic and other CNS targeted compounds.

Effects of Saponins from the Root Bark of Aralia elata on the Transport of Chondroitin Sulfate in Caco-2 Cell Monolayers and Rats

We investigated the intestinal absorption enhancing effect of the saponins from the root bark of Aralia elata (SRBAE) in Caco-2 cell monolayers and rats. SRBAE at concentrations of 0.04% and 0.08% (w/v) decreased the transepithelial electrical resistance (TEER) values and increased the paracellular uptake of chondroitin sulfates (CSs) having different molecular weights (MW 500, 4500, and 18000) in a dose-dependent manner. We also evaluated the cytotoxicity of SRBAE to determine its proper concentration as an absorption enhancer. MTT assay and trypan blue exclusion test indicated that the cytotoxicity of SRBAE at concentrations of 0.04% and 0.08% was negligible. CS (MW 18000) was orally administered with or without SRBAE to rats. The oral administration of SRBAE (250 mg/kg) in 1 h increased the intestinal absorption of CS, by 4.9-fold versus the control (CS alone). Histological examination of the gastrointestinal tissues showed that SRBAE did not cause any damage to tissues. In conclusion, our results suggest that SRBAE acts as an efficient absorption enhancer and makes it easier for hydrophilic molecules to penetrate the intestinal epithelium.

Differential expression of E-cadherin, N-cadherin and beta-catenin in proximal and distal segments of the rat nephron

BACKGROUND

The classical cadherins such as E- and N-cadherin are Ca2+-dependent cell adhesion molecules that play important roles in the development and maintenance of renal epithelial polarity. Recent studies have shown that a variety of cadherins are present in the kidney and are differentially expressed in various segments of the nephron. However, the interpretation of these findings has been complicated by the fact that the various studies focused on different panels of cadherins and utilized different species. Moreover, since only a few of the previous studies focused on the rat, information regarding the expression and localization of renal cadherins in this important species is lacking. In the present study, we have employed dual immunofluorescent labeling procedures that utilized specific antibodies against either E- or N-cadherin, along with antibodies that target markers for specific nephron segments, to characterize the patterns of cadherin expression in frozen sections of adult rat kidney.

RESULTS

The results showed that N-cadherin is the predominant cadherin in the proximal tubule, but is essentially absent in other nephron segments. By contrast, E-cadherin is abundant in the distal tubule, collecting duct and most medullary segments, but is present only at very low levels in the proximal tubule. Additional results revealed different patterns of N-cadherin labeling along various segments of the proximal tubule. The S1 and S2 segments exhibit a fine threadlike pattern of labeling at the apical cell surface, whereas the S3 segment show intense labeling at the lateral cell-cell contacts.

CONCLUSIONS

These results indicate that E- and N-cadherin are differentially expressed in the proximal and distal tubules of rat kidney and they raise the possibility that differences in cadherin expression and localization may contribute to the differences in the susceptibility of various nephron segments to renal pathology or nephrotoxic injury.

Expression, purification, and structural study of the EC4 domain of E-cadherin

The objective of this work was to produce unlabeled and 15N-labeled EC4 domain protein from E-cadherin for studying its structure and binding properties to other EC domains as well as to E-cadherin peptides. The EC4 domain of E-cadherin was expressed in Escherichia coli from the vector pASK-IBA6 and localized in the periplasmic space of E. coli. This protein contains a Streptag sequence at the N-terminus, and thus was purified using a Strep-Tactin affinity column. However, at high concentrations the 15N-labeled EC4 protein showed an unstable conformation. Conditions for stabilizing the conformation of this protein were evaluated using CD spectroscopy. The CD results showed that this protein has high conformational stability in Tris buffer at pH 6.0 in the presence of 10 mM calcium chloride.

Absorption enhancers for nasal drug delivery

This paper describes the basic concepts for the transmucosal delivery of drugs, and in particular the use of the nasal route for delivery of challenging drugs such as polar low-molecular-weight drugs and peptides and proteins. Strategies for the exploitation of absorption enhancers for the improvement of nasal delivery are discussed, including consideration of mechanisms of action and the correlation between toxic effect and absorption enhancement. Selected enhancer systems, such as cyclodextrins, phospholipids, bioadhesive powder systems and chitosan, are discussed in detail. Examples of the use of these enhancers in preclinical and clinical studies are given. Methods for assessing irritancy and damage to the nasal membrane from the use of absorption enhancers are also described. Finally, the mucosal use of absorption enhancers (chitosan) for the improved nasal delivery of vaccines is reported with reference to recent phase I/II clinical studies.

Cadmium alters the localization of N-cadherin, E-cadherin, and beta-catenin in the proximal tubule epithelium

Recent studies on proximal tubule-derived cells in culture have shown that Cd has relatively specific damaging effects on the cadherin-dependent junctions between the cells. The objective of the present study was to determine whether Cd can affect cadherin-dependent junctions in the proximal tubule epithelium in vivo. Male Sprague-Dawley rats received subcutaneous injections of Cd (0.6 mg/kg in isotonic saline, 5 days per week for up to 6 weeks). One day each week, 24-h urine samples were collected and analyzed for protein and creatinine. After 5-6 weeks, the Cd-treated animals developed significant proteinuria, with no change in creatinine excretion. Visualization of pan-cadherin immunoreactive materials by immunoperoxidase labeling showed that Cd caused a marked reduction in the intensity of cadherin labeling associated with the apical and the basolateral surfaces of the epithelial cells of the proximal tubule, but no change in the pattern of cadherin labeling in other segments of the nephron. Results of studies utilizing specific antibodies against N-cadherin, E-cadherin, and beta-catenin showed changes in the localization of all three molecules in the proximal tubule. Assessment of cell membrane integrity with trypan blue and ethidium homodimer showed no overt evidence of death in the proximal tubule epithelial cells. Additional results showed that Cd caused only a slight increase in the total levels of glutathione and no significant peroxidation of membrane lipids, indicating only a modest level of oxidative stress. These results indicate that Cd can disrupt cadherin-dependent cell-cell junctions in the proximal tubule, and they raise the possibility that a loss of cadherin-mediated adhesion may contribute to the nephrotoxic effects of Cd.

Safety and efficiency of modulating paracellular permeability to enhance airway epithelial gene transfer in vivo

We evaluated the safety of agents that enhance gene transfer by modulating paracellular permeability. Lactate dehydrogenase (LDH) and cytokine release were measured in polarized primary human airway epithelial (HAE) cells after lumenal application of vehicle, ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA), sodium caprate (C10), or sodium laurate (C12). Lung toxicity was assessed after tracheobronchial instillation to murine airways and the relative ability of these agents to enhance in vivo adenoviral gene transfer was evaluated. Lumenal C12 increased LDH release in vitro, but C10 and EGTA did not. Increased levels of interleukin 8 (IL-8) were secreted from EGTA-pretreated cystic fibrosis HAE cells after apical application of Pseudomonas aeruginosa (10(8) CFU/ml), whereas IL-8 secretion from C10- and C12-pretreated cells was not different from controls. In vivo toxicity studies demonstrated no effect of EGTA, C10, or C12 on weight gain, lung edema, or bronchoalveolar lavage fluid (BALF) albumin. EGTA increased BALF cell counts, neutrophils, and murine (m) macrophage inflammatory protein 2, mKC, mIL-6, and mIL-1 beta levels. C10 had no effect on BALF cell counts or LDH, but increased murine tumor necrosis factor alpha. C12 increased BALF LDH, neutrophils, and mIL-6 levels. Histopathological analysis revealed mild focal lung inflammation more frequently in the EGTA, C10, and C12 groups than in vehicle controls, with greater intensity in the C12 group relative to the other groups. C10 and C12 also increased airway responsiveness to methacholine challenge compared with control and EGTA groups. Adenoviral gene transfer to murine trachea in vivo was enhanced more efficiently by C10 than by C12 or EGTA. Thus, the different toxicities may permit the selection of agents that enhance gene transfer with minimal adverse effects.

Increasing paracellular porosity by E-cadherin peptides: discovery of bulge and groove regions in the EC1-domain of E-cadherin

PURPOSE

The objective of this work is to evaluate the ability of peptides derived from the bulge (HAV-peptides) and groove (ADT-peptides) regions of E-cadherin EC1-domain to increase the paracellular porosity of the intercellular junctions of Madin-Darby canine kidney (MDCK) cell monolayers.

METHODS

Peptides were synthesized using a solid-phase method and were purified using semi-preparative HPLC. MDCK monolayers were used to evaluate the ability of cadherin peptides to modulate cadherin-cadherin interactions in the intercellular junctions. The increase in intercellular junction porosity was determined by the change in transepithelial electrical resistance (TEER) values and the paracellular transport of 14C-mannitol.

RESULTS

HAV- and ADT-peptides can lower the TEER value of MDCK cell monolayers and enhance the paracellular permeation of 14C-mannitol. HAV- and ADT-decapeptides can modulate the intercellular junctions when they are added from the basolateral side but not from the apical side; on the other hand. HAV- and ADT-hexapeptides increase the paracellular porosity of the monolayers when added from either side. Conjugation of HAV- and ADT-peptides using omega-aminocaproic acid can only work to modulate the paracellular porosity when ADT-peptide is at the N-terminus and HAV-peptide is at the C-terminus; because of its size, the conjugate can only modulate the intercellular junction when added from the basolateral side.

CONCLUSIONS

Peptides from the bulge and groove regions of the EC1 domain of E-cadherin can inhibit cadherin-cadherin interactions, resulting in the opening of the paracellular junctions. These peptides may be used to improve paracellular permeation of peptides and proteins. Furthermore, this work suggests that both groove and bulge regions of EC-domain are important for cadherin-cadherin interactions.

Zonula occludens toxin increases the permeability of molecular weight markers and chemotherapeutic agents across the bovine brain microvessel endothelial cells

The purpose of this study was to examine the ability of Zonula occludens toxin (Zot) to reversibly open tight junctions in bovine brain microvessel endothelial cells (BBMECs) to enhance drug delivery via the paracellular pathway. Transport across BBMEC monolayers was examined for molecular weight markers and chemotherapeutic agents ([(14)C]sucrose, [(14)C]inulin, [(3)H]propranolol, [(3)H]doxorubicin, and [(14)C]paclitaxel) with Zot (0.0-4.0 microg/mL). TEER of monolayers was measured to assess effect and reversibility of Zot. Cell viability of BBMEC in the presence of Zot was assessed by trypan blue exclusion staining. Apparent permeability (P(app)), enhancement ratio (R), and percent increase in transport determined were statistically compared by ANOVA. A significant increase (p < 0.05) in P(app) was observed for the transport of [(14)C]sucrose, [(14)C]inulin, [(3)H]doxorubicin, and [(14)C]paclitaxel at a 4.0 microg/mL concentration of Zot. A significant concentration-dependent decrease in TEER was observed on treatment with Zot with rapid reversal to baseline after removal. Zot (4 micro/ml) was found to be nontoxic to the BBMECs after 2 hours incubation. In conclusion, Zot increased paracellular transport across the BBMEC in a reversible, concentration-dependent manner. Modulation of paracellular transport with Zot may be used to increase the brain permeability of potent central nervous system-active drugs, including anticancer agents.

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.

E-Cadherin, beta -Catenin and cadmium carcinogenesis

Cadmium (Cd(2+)) is an important industrial and environmental pollutant that has been classified as a human carcinogen. Studies reported in the literature indicate that cadmium may play a role in both the initiation of cancer, by activating oncogenes, and in the progression of cancer, by increasing the metastatic potential of existing cancer cells. However, the mechanisms underlying these effects have yet to be elucidated. Recent studies from our laboratory have shown that cadmium can disrupt the tight junctions between many types of epithelial cells by interfering with the normal function of E-cadherin, a Ca(2+)-dependent cell adhesion molecule that plays a key role in epithelial cell-cell adhesion. This finding may be especially significant because a large volume of evidence indicates that the disruption of E-cadherin-mediated cell adhesion can trigger the beta-catenin-mediated activation of oncogenes in epithelial cells and increase the invasive potential of existing epithelial-derived cancers. The hypothesis that we are proposing is that the cadmium-induced disruption of E-cadherin dependent cell-cell junctions may represent a pivotal step in both the initiation of cancer by cadmium and in the tumor promoting actions of cadmium.

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.

Use of alveolar cell monolayers of varying electrical resistance to measure pulmonary peptide transport

The apparent permeability coefficient (P(app)) of two fluorescently tagged model hydrophilic peptides, acXASNH(2) and acXAS(GAS)(7)NH(2), and (14)C-mannitol across monolayers of cultured rat alveolar epithelial cells of varying transepithelial electrical resistance (TER) has been examined. In line with their design features, the peptides were not degraded under the conditions of the test. Furthermore, no concentration dependence of transport of the tripeptide acXASNH(2) was observed over the concentration range studied, nor was any directional transport seen for either of the model peptides, indicating that under the conditions of the test they were not substrates for any transporters or efflux pumps. From the hydrophilic nature of the peptides (as assessed by their log P), and their inverse dependence of transport with molecular weight and TER, it was assumed that the peptides were transported across the cell monolayer passively via the paracellular route. The observed P(app) for the transport of (14)C-mannitol and the peptides across rat alveolar epithelial cell monolayers were found to be inversely (though not linearly) related to the measured TER and could be well-modeled assuming the presence of two populations of "pores" in the cell monolayer, namely, cylindrical pores of diameter 1.5 nm and large pores of diameter 20 nm. The relative populations of the two types of pores varied with the TER of the monolayer, with the number of large pores decreasing with an increase in TER (and the number of small pores taken as fixed). These results suggest that if the cell monolayer is well characterized with respect to the passage of a range of probe molecules across monolayers of varying electrical resistance, it should be possible to predict the P(app) of any hydrophilic peptide or drug crossing the membrane by the paracellular route at any desired TER using a monolayer of any electrical resistance, above a minimum value.

Dodecylphosphocholine-mediated enhancement of paracellular permeability and cytotoxicity in Caco-2 cell monolayers

The intestinal epithelium is a significant barrier for oral absorption of hydrophilic drugs because they cannot easily traverse the lipid bilayer of the cell membrane and their passage through the intercellular space (paracellular transport) is restricted by the tight junctions. In this report we show that dodecylphosphocholine (DPC) can improve the paracellular permeability of hydrophilic compounds across Caco-2 cell monolayers by modulating the tight junctions. The results show that the alkyl chain as well as the zwitterionic head group of DPC are required for its activity. DPC appears to act by modulating the permeability of tight junctions as evidenced by the fact that treatment of Caco-2 cell monolayers by this agent results in a decreased transepithelial electrical resistance (TEER), increased permeability of paracellular markers (e. g., mannitol) with no change in the permeability of the transcellular marker testosterone, and redistribution of the tight junction-associated protein ZO-1. The effect of DPC on Caco-2 cells (e.g., decrease in TEER) is reversible, and is not caused by gross cytotoxicity (as indicated by the MTT test) or by nonspecific disruption of the cell membrane (as indicated by only slight nuclear staining due to the nonpermeable DNA-specific dye propidium iodide). We propose in the present study a parameter, potency index, that allows comparison of various enhancers of paracellular transport in relation to their cytotoxicity. The potency index is a ratio between the IC(50) value (concentration at which 50% inhibition of control mitochondrial dehydrogenase activity occurs in the MTT test) and the EC(50) value (concentration at which TEER drops to 50% of its control (untreated) value). By this parameter, DPC is significantly safer than the commonly used absorption enhancer palmitoyl carnitine (PC), which has the potency index of approximately 1 (i.e., no separation between effective and toxic concentration).

Structure-activity relationships for enhancement of paracellular permeability by 2-alkoxy-3-alkylamidopropylphosphocholines across Caco-2 cell monolayers

The oral route is the preferred route of delivery for a large number of drug molecules. However, the intestinal epithelium presents a formidable barrier for delivery of drugs into systemic circulation. Phospholipids are among compounds that enhance the absorption of drugs across the intestinal epithelium. In this paper, we describe structure-activity relationships for phospholipid derivatives as enhancers of paracellular permeability across Caco-2 cell monolayers. In a series of 2-alkoxy-3-alkylamidopropylphosphocholine derivatives, compounds with a long chain at C-3 (R3) and short chain at C-2 (R2) were potent in causing a decrease in transepithelial electrical resistance (TEER) and an increase in mannitol transport, but also showed significant cytotoxicity. Compounds with 9-11 carbons at C-3 and 6-10 carbons at C-2 provided good separation (up to 2.7-fold) between activity and cytotoxicity. Notably, a good correlation (r2 = 0.93) was observed between EC(50) (TEER) [concentration that caused a drop in TEER to 50% of its control (untreated) value] and EC10x (mannitol) [concentration that caused 10-fold increase in mannitol transport over the control (untreated) value], confirming that a decrease in TEER is associated with enhanced permeability of the hydrophilic compounds across Caco-2 cell monolayers. Compounds with medium to long carbon chains at C-2 and C-3, and the total carbons in the alkyl chains > 20, showed poor activity and no cytotoxicity.

Saturable transport of H2-antagonists ranitidine and famotidine across Caco-2 cell monolayers

The purpose of this study was to investigate the mechanism by which the H2-antagonists ranitidine and famotidine interacted with the paracellular space during their transport across Caco-2 cell monolayers. Transport experiments with ranitidine and famotidine across Caco-2 cell monolayers were performed to determine the apical-to-basolateral flux at various concentrations. Kinetic analysis of the transport data showed that ranitidine and famotidine were transported by both saturable and nonsaturable processes. Na+, K+-ATPase inhibitor ouabain and metabolic inhibitors sodium azide + 2-deoxy-D-glucose did not affect ranitidine transport, suggesting that the active transport was not involved. Famotidine and some other guanidine-containing compounds, e.g., guanethidine, Arg-Gly, L-arginine methyl ester, and L-argininamide, inhibited the transport of ranitidine, whereas other guanidine-containing compounds with an additional negative charge, e.g., L-arginine, did not. 2,4, 6-Triaminopyrimidine (TAP), an inhibitor of paracelluar cationic conductance, also inhibited the transport of both ranitidine and famotidine. On the basis of these results, it is proposed that the saturable transport of ranitidine and famotidine across Caco-2 cell monolayers appears to be via a facilitated diffusion process mediated by the paracellular anionic sites. This mechanism is consistent with the observation that ranitidine and famotidine caused a concentration-dependent increase in transepithelial electrical resistance (TEER) across Caco-2 cell monolayers, presumably by blocking the paracellular anionic sites and thus inhibiting the flux of cations (e.g., Na+).

Comparison of the effects of potential parenteral vehicles for poorly water soluble anticancer drugs (organic cosolvents and cyclodextrin solutions) on cultured endothelial cells (HUV-EC)

The effect of dilution of parenteral vehicles (organic cosolvent and 0.1 M cyclodextrin solutions) on cultured endothelial cells (HUV-EC) were compared in vitro. Cell morphology was observed by phase contrast light microscopy and cell viability by measuring 3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction or intracellular lactate dehydrogenase (LDH) activity and total protein. Disruption of the HUV-EC monolayer was observed at dilutions of 1 in 20 for the melphalan and PEP cosolvents, 1 in 100 for an investigational drug cosolvent, and 1 in 10 for 0.1 M dimethyl-beta-cyclodextrin. In comparison, 0.1 M SBE7M- and HP-beta-cyclodextrin caused only minor disruption at a 1 in 5 dilution. MTT reduction, intracellular LDH, and total protein were decreased following exposure to 1 in 10 dilution of the melphalan cosolvent. For other test solutions, intracellular LDH activity and total protein were measured, and reductions were observed following exposure to 1 in 10, 20, and 50 dilutions of the investigational drug cosolvent and 1 in 5 dilution of DM-beta-cyclodextrin (0.1 M). At a dilution of 1 in 10, no delayed toxicity was observed for cosolvents or cyclodextrin solutions. Hence, 0.1 M SBE7M- or HP-beta-cyclodextrin formulations may be less damaging to the venous endothelium at the site of injection than organic cosolvent formulations.

Characterization of furazolidone apical-related effects to human polarized intestinal cells

In studying the effects of furazolidone (FZ) on the human intestinal Caco-2 cell line grown on microporous membrane, we have previously demonstrated a higher toxicity when the compound was administered at the apical (AP) side than at the basolateral (BL) side. Moreover, we have also shown the production, in the intact cells, of a nitroanion radical from FZ by a cytochrome c P450 reductase. The aim of the present study was to investigate which specific cell structures and functions are involved in the observed domain-related toxicity. The relevance of alterations in integrity and selective properties of the intestinal barrier as first-pass site for ingested molecules is also discussed. We have confirmed that, as expected, the Caco-2 cells are protected from FZ injury by a specific inhibitor of the cytochrome c P450 reductase, and we have shown that this protection is more active on the apical side of the cells. In sublethal conditions, FZ causes increased permeability to 3H-mannitol and, to a different extent, to 3H-inulin. Again the effect is higher when the cells are apically exposed. We have thus examined the tight junctions morphology: a disruption of the apical perijunctional actin-bound cytoskeleton was detected by rhodamine-phalloidin staining and microtubule disorganization by antitubulin fluoresceinated antibodies. Again, the effect was more evident when the cells were apically treated with FZ. Preferential transport and accumulation of the compound by active transport mechanisms could be excluded, since transport of FZ was linear and no intracellular accumulation was detected either from the AP and or the BL sides. All together these results may suggest that the AP formation of the active metabolite and its possible reactivity with SH groups of perijunctional microfilaments could be responsible of the higher FZ apical toxicity. This study shows that polarized differentiated cells are very interesting in vitro models to investigate specific cellular domains as targets of toxic effects and to detect subtle changes that may be induced, in absence of cell death, in specialized epithelial layers.