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Background: During inhalation, airborne particles such as particulate matter ≤ 2.5 μm (PM 2.5 ), can deposit and accumulate on the alveolar epithelial tissue. In vivo studies have shown that fractions of PM 2.5 can cross the alveolar epithelium to blood circulation, reaching secondary organs beyond the lungs. However, approaches to quantify the translocation of particles across the alveolar epithelium in vivo and in vitro are still not well established. In this study, methods to assess the translocation of standard diesel exhaust particles (DEPs) across permeable polyethylene terephthalate (PET) inserts at 0.4, 1, and 3 μm pore sizes were first optimized with transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-VIS), and lock-in thermography (LIT), which were then applied to study the translocation of DEPs across human alveolar epithelial type II (A549) cells. A549 cells that grew on the membrane (pore size: 3 μm) in inserts were exposed to DEPs at different concentrations from 0 to 80 µg.mL - 1 ( 0 to 44 µg.cm - 2 ) for 24 h. After exposure, the basal fraction was collected and then analyzed by combining qualitative (TEM) and quantitative (UV-VIS and LIT) techniques to assess the translocated fraction of the DEPs across the alveolar epithelium in vitro., Results: We could detect the translocated fraction of DEPs across the PET membranes with 3 μm pore sizes and without cells by TEM analysis, and determine the percentage of translocation at approximatively 37% by UV-VIS (LOD: 1.92 µg.mL - 1 ) and 75% by LIT (LOD: 0.20 µg.cm - 2 ). In the presence of cells, the percentage of DEPs translocation across the alveolar tissue was determined around 1% at 20 and 40 µg.mL - 1 (11 and 22 µg.cm - 2 ), and no particles were detected at higher and lower concentrations. Interestingly, simultaneous exposure of A549 cells to DEPs and EDTA can increase the translocation of DEPs in the basal fraction., Conclusion: We propose a combination of analytical techniques to assess the translocation of DEPs across lung tissues. Our results reveal a low percentage of translocation of DEPs across alveolar epithelial tissue in vitro and they correspond to in vivo findings. The combination approach can be applied to any traffic-generated particles, thus enabling us to understand their involvement in public health., (© 2024. The Author(s).)

Transepithelial electrical resistance (TEER) measures electrical resistance across epithelial tissue barriers involving confluent layer(s) of cells. TEER values act as a prerequisite for determining the barrier integrity of cells, which play a key role in evaluating the transport of drugs, materials or chemicals of interest across an epithelial barrier. The measurements can be performed non-invasively by measuring ohmic resistance across a defined area. Thus, the TEER values are reported in Ω·cm 2 . In vitro epithelial models are typically assembled on semi-permeable inserts providing two-chamber compartments, and the majority of the studies use inserts with polyethylene terephthalate (PET) membranes. Recently, new inserts with different membrane types and properties have been introduced. However, the TEER values presented so far did not allow a direct comparison. This study presents the characterization of selected epithelial tissues, i.e., lung, retina, and intestine, grown on an ultra-thin ceramic microporous permeable insert (SiMPLI) and PET membranes with different properties, i.e., thickness, material, and pore numbers. We verified the epithelial cell growth on both inserts via phase-contrast and confocal laser scanning microscope imaging. Barrier characteristics were assessed by TEER measurements and also by evaluating the permeability of fluorescein isothiocyanate through cell layers. The findings indicated that background TEER value calculations and the available surface area for cell growth must be thoroughly assessed when new inserts are introduced, as the values cannot be directly compared without re-calculations. Finally, we proposed electrical circuit models highlighting the contributors to TEER recordings on PET and SiMPLI insert membranes. This study paves the way for making the ohmic-based evaluation of epithelial tissues' permeability independent of the material and geometry of the insert membrane used for cell growth., Competing Interests: Declaration of Competing Interest Silvia Angeloni is the CEO - Founder of SiMPLInext SA. The authors declare that there are no conflicts of interest., (Copyright © 2023. Published by Elsevier B.V.)