Functional and cytometric examination of different human lung epithelial cell types as drug transport barriers

Interaction of Neisseria meningitidis carrier and disease isolates of MenB cc32 and MenW cc22 with epithelial cells of the nasopharyngeal barrier

Neisseria meningitidis (Nm, the meningococcus) is considered an asymptomatic colonizer of the upper respiratory tract and a transient member of its microbiome. It is assumed that the spread of N. meningitidis into the bloodstream occurs via transcytosis of the nasopharyngeal epithelial barrier without destroying the barrier layer. Here, we used Calu-3 respiratory epithelial cells that were grown under air-liquid-interface conditions to induce formation of pseudostratified layers and mucus production. The number of bacterial localizations in the outer mucus, as well as cellular adhesion, invasion and transmigration of different carrier and disease N. meningitidis isolates belonging to MenB:cc32 and MenW:cc22 lineages was assessed. In addition, the effect on barrier integrity and cytokine release was determined. Our findings showed that all strains tested resided primarily in the outer mucus layer after 24 h of infection (>80%). Nonetheless, both MenB:cc32 and MenW:cc22 carrier and disease isolates reached the surface of the epithelial cells and overcame the barrier. Interestingly, we observed a significant difference in the number of bacteria transmigrating the epithelial cell barrier, with the representative disease isolates being more efficient to transmigrate compared to carrier isolates. This could be attributed to the capacity of the disease isolates to invade, however could not be assigned to expression of the outer membrane protein Opc. Moreover, we found that the representative meningococcal isolates tested in this study did not damage the epithelial barrier, as shown by TEER measurement, FITC-dextran permeability assays, and expression of cell-junction components.

SARS-CoV-2 infection alters mitochondrial and cytoskeletal function in human respiratory epithelial cells mediated by expression of spike protein

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, SCV2), which has resulted in higher morbidity and mortality rate than other respiratory viral infections, such as Influenza A virus (IAV) infection. Investigating the molecular mechanisms of SCV2-host infection vs IAV is vital in exploring antiviral drug targets against SCV2. We assessed differential gene expression in human nasal cells upon SCV2 or IAV infection using RNA sequencing. Compared to IAV, we observed alterations in both metabolic and cytoskeletal pathways suggestive of epithelial remodeling in the SCV2-infected cells, reminiscent of pathways activated as a response to chronic injury. We found that spike protein interaction with the epithelium was sufficient to instigate these epithelial responses using a SCV2 spike pseudovirus. Specifically, we found downregulation of the mitochondrial markers SIRT3 and TOMM22. Moreover, SCV2 spike infection increased extracellular acidification and decreased oxygen consumption rate in the epithelium. In addition, we observed cytoskeletal rearrangements with a reduction in the actin-severing protein cofilin-1 and an increase in polymerized actin, indicating epithelial cytoskeletal rearrangements. This study revealed distinct epithelial responses to SCV2 infection, with early mitochondrial dysfunction in the host cells and evidence of cytoskeletal remodeling that could contribute to the worsened outcome in COVID-19 patients compared to IAV patients. These changes in cell structure and energetics could contribute to cellular resilience early during infection, allowing for prolonged cell survival and potentially paving the way for more chronic symptoms. IMPORTANCE COVID-19 has caused a global pandemic affecting millions of people worldwide, resulting in a higher mortality rate and concerns of more persistent symptoms compared to influenza A. To study this, we compare lung epithelial responses to both viruses. Interestingly, we found that in response to SARS-CoV-2 infection, the cellular energetics changed and there were cell structural rearrangements. These changes in cell structure could lead to prolonged epithelial cell survival, even in the face of not working well, potentially contributing to the development of chronic symptoms. In summary, these findings represent strategies utilized by the cell to survive the infection but result in a fundamental shift in the epithelial phenotype, with potential long-term consequences, which could set the stage for the development of chronic lung disease or long COVID-19.

The Cultivation Modality and Barrier Maturity Modulate the Toxicity of Industrial Zinc Oxide and Titanium Dioxide Nanoparticles on Nasal, Buccal, Bronchial, and Alveolar Mucosa Cell-Derived Barrier Models

As common industrial by-products, airborne engineered nanomaterials are considered important environmental toxins to monitor due to their potential health risks to humans and animals. The main uptake routes of airborne nanoparticles are nasal and/or oral inhalation, which are known to enable the transfer of nanomaterials into the bloodstream resulting in the rapid distribution throughout the human body. Consequently, mucosal barriers present in the nose, buccal, and lung have been identified and intensively studied as the key tissue barrier to nanoparticle translocation. Despite decades of research, surprisingly little is known about the differences among various mucosa tissue types to tolerate nanoparticle exposures. One limitation in comparing nanotoxicological data sets can be linked to a lack of harmonization and standardization of cell-based assays, where (a) different cultivation conditions such as an air-liquid interface or submerged cultures, (b) varying barrier maturity, and (c) diverse media substitutes have been used. The current comparative nanotoxicological study, therefore, aims at analyzing the toxic effects of nanomaterials on four human mucosa barrier models including nasal (RPMI2650), buccal (TR146), alveolar (A549), and bronchial (Calu-3) mucosal cell lines to better understand the modulating effects of tissue maturity, cultivation conditions, and tissue type using standard transwell cultivations at liquid-liquid and air-liquid interfaces. Overall, cell size, confluency, tight junction localization, and cell viability as well as barrier formation using 50% and 100% confluency was monitored using trans-epithelial-electrical resistance (TEER) measurements and resazurin-based Presto Blue assays of immature (e.g., 5 days) and mature (e.g., 22 days) cultures in the presence and absence of corticosteroids such as hydrocortisone. Results of our study show that cellular viability in response to increasing nanoparticle exposure scenarios is highly compound and cell-type specific (TR146 6 ± 0.7% at 2 mM ZnO (ZnO) vs. ~90% at 2 mM TiO2 (TiO2) for 24 h; Calu3 93.9 ± 4.21% at 2 mM ZnO vs. ~100% at 2 mM TiO2). Nanoparticle-induced cytotoxic effects under air-liquid cultivation conditions declined in RPMI2650, A549, TR146, and Calu-3 cells (~0.7 to ~0.2-fold), with increasing 50 to 100% barrier maturity under the influence of ZnO (2 mM). Cell viability in early and late mucosa barriers where hardly influenced by TiO2 as well as most cell types did not fall below 77% viability when added to Individual ALI cultures. Fully maturated bronchial mucosal cell barrier models cultivated under ALI conditions showed less tolerance to acute ZnO nanoparticle exposures (~50% remaining viability at 2 mM ZnO for 24 h) than the similarly treated but more robust nasal (~74%), buccal (~73%), and alveolar (~82%) cell-based models.

Variable disruption of epithelial monolayers by Neisseria meningitidis carriage isolates of the hypervirulent MenW cc11 and MenY cc23 lineages

Colonization of mucosal tissues by Neisseria meningitidis requires adhesion mediated by the type IV pilus and multiple outer-membrane proteins. Penetration of the mucosa and invasion of epithelial cells are thought to contribute to host persistence and invasive disease. Using Calu-3 cell monolayers grown at an air-liquid interface, we examined adhesion, invasion and monolayer disruption by carriage isolates of two clonal complexes of N. meningitidis. Carriage isolates of both the serogroup Y cc23 and the hypervirulent serogroup W cc11 lineages exhibited high levels of cellular adhesion, and a variable disruption phenotype across independent isolates. Inactivation of the gene encoding the main pilus sub-unit in multiple cc11 isolates abrogated both adhesive capacity and ability to disrupt epithelial monolayers. Contrastingly, inactivation of the phase-variable opa or nadA genes reduced adhesion and invasion, but not disruption of monolayer integrity. Adherence of tissue-disruptive meningococci correlated with loss of staining for the tight junction protein, occludin. Intriguingly, in a pilus-negative strain background, we observed compensatory ON switching of opa genes, which facilitated continued adhesion. We conclude that disruption of epithelial monolayers occurs in multiple meningococcal lineages but can vary during carriage and is intimately linked to pilus-mediated adhesion.

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

In vitro evaluation of drug delivery behavior for inhalable amorphous nanoparticle formulations in a human lung epithelial cell model

Respiratory tract infections caused by multidrug-resistant (MDR) Gram-negative bacteria such as Pseudomonas aeruginosa are serious burdens to public health, especially in cystic fibrosis patients. The combination of colistin, a cationic polypeptide antibiotic, and ivacaftor, a cystic fibrosis transmembrane regulator (CFTR) protein modulator, displays a synergistic antibacterial effect against P. aeruginosa. The primary aim of the present study is to investigate the transport, accumulation and toxicity of a novel nanoparticle formulation containing colistin and ivacaftor in lung epithelial Calu-3 cells. The cell viability results demonstrated that ivacaftor alone or in combination with colistin in the physical mixture showed significant toxicity at an ivacaftor concentration of 10 μg/mL or higher. However, the cellular toxicity was significantly reduced in the nanoparticle formulation. Ivacaftor transport into the cells reached a plateau rapidly as compared to colistin. Colistin transport across the Calu-3 cell monolayer was less than ivacaftor. A substantial amount (46-83%) of ivacaftor, independent of dose, was accumulated in the cell monolayer following transport from the apical into the basal chamber, whereas the intracellular accumulation of colistin was relatively low (2-15%). The nanoparticle formulation significantly reduced the toxicity of colistin and ivacaftor to Calu-3 cells by reducing the accumulation of both drugs in the cell and potential protective effects by bovine serum albumin (BSA), which could be a promising safer option for the treatment of respiratory infections caused by MDR P. aeruginosa.

[Intrapulmonary Pharmacokinetics and Drug Distribution Characteristics for the Treatment of Respiratory Diseases]

This study was designed to clarify the intrapulmonary pharmacokinetics and distribution characteristics of drugs in order to develop better therapies for respiratory diseases, including respiratory infections and pulmonary fibrosis. The distribution characteristics of three macrolide antimicrobial agents-clarithromycin, azithromycin, and telithromycin-in plasma, lung epithelial lining fluid (ELF), and alveolar macrophages (AMs), were examined for the optimization of antimicrobial therapy. The time course of the uptake of these agents in ELF and AMs, following oral administration to rats, resulted in markedly higher concentrations than that in plasma. The high concentration of the agents in AMs was due to their sustained distribution to ELF via multidrug resistance protein 1 and to high uptake by AMs themselves via active transport mechanisms and trapping and/or binding in acidic organelles. The intrapulmonary pharmacokinetics of aerosolized model compounds administered to animals with bleomycin-induced pulmonary fibrosis via aerosol formulations of model compounds (MicroSprayer) were then evaluated. The concentrations of these compounds in the plasma of pulmonary fibrotic rats were markedly higher than in that of control rats. The expression of epithelial tight junctions decreased in pulmonary fibrotic lesions. The accumulation of extracellular matrix inhibited the intrapulmonary distribution of aerosolized model compounds, indicating that aerosolized drugs are easily absorbed after leakage through damaged alveolar epithelia, but cannot become widely distributed in the lungs because of interruption by the extracellular matrix. This review provides useful findings for the development of therapies for respiratory infections and pulmonary fibrosis.

Evaluation of epithelial transport and oxidative stress protection of nanoengineered curcumin derivative-cyclodextrin formulation for ocular delivery

Ocular drug delivery has been a well-known route for the drug administration for the treatment of ocular diseases. However, numerous anatomical and physiological barriers prevailing in the eye itself create considerable challenges for achieving the necessitated therapeutic efficacy along with ocular bioavailability. However, recent advances in nanoengineered strategies hold definite promises in terms of devising improved ophthalmic medicines for the effective drug delivery to target the sites with enhanced ocular bioavailability. Curcumin, a hydrophobic polyphenol yellow colored compound, and its metabolic reduced product, tetrahydrocurcumin (THC), have been known for their beneficial pharmacological functions, such as anti-inflammatory or anti-oxidant activities at various tissue sites. However, the low aqueous solubility of these compounds results in their poor bioavailability, thereby limiting their widespread application. Therefore, in the present study, we investigated the changes in drug solubility by forming inclusion complexes with different derivatives of hydroxypropyl (HP)-cyclodextrins (CD). To this end, the spray drying technique was used for nanoengineering curcumin or THC-loaded formulations to improve the stability of formulations during the storage. The formulations were characterized in terms of physicochemical properties and cellular permeability. The results demonstrated that the encapsulation of curcumin (or THC) into the HP-CDs significantly increased the drug solubility and enhanced the corneal and retinal epithelial permeability. Curcumin or THC complexes in HP-CDs with improved bioavailability also induced anti-oxidant activity (SOD1, CAT1, and HMOX1) in higher levels in the ocular epithelial cells and showed oxidative protection effects in rabbit cornea tissues that will boost up their application in ocular medicine.

Murine alveolar epithelial cells and their lentivirus-mediated immortalisation

In this study, we describe the isolation and immortalisation of primary murine alveolar epithelial cells (mAEpC), as well as their epithelial differentiation and barrier properties when grown on Transwell® inserts. Like human alveolar epithelial cells (hAEpC), mAEpC transdifferentiate in vitro from an alveolar type II (ATII) phenotype to an ATI-like phenotype and exhibit features of the air-blood barrier, such as the establishment of a thin monolayer with functional tight junctions (TJs). This is demonstrated by the expression of TJ proteins (ZO-1 and occludin) and the development of high transepithelial electrical resistance (TEER), peaking at 1800Ω ·cm². Transport across the air-blood barrier, for general toxicity assessments or preclinical drug development, is typically studied in mice. The aim of this work was the generation of novel immortalised murine lung cell lines, to help meet Three Rs requirements in experimental testing and research. To achieve this goal, we lentivirally transduced mAEpC of two different mouse strains with a library of 33 proliferation-promoting genes. With this immortalisation approach, we obtained two murine alveolar epithelial lentivirus-immortalised (mAELVi) cell lines. Both showed similar TJ protein localisation, but exhibited less prominent barrier properties (TEERmax ~250Ω·cm²) when compared to their primary counterparts. While mAEpC demonstrated their suitability for use in the assessment of paracellular transport rates, mAELVi cells could potentially replace mice for the prediction of acute inhalation toxicity during early ADMET studies.