Abstract

The study of epithelial barrier function is essential for fundamental understanding of disease processes, development of new therapeutic treatments, and investigation of compound safety. The gold standard barrier integrity measurement in epithelial models is the Trans Epithelial Electrical Resistance (TEER). The electrical properties of an epithelial layer are in a direct correlation to aspects such tight junctions, confluency, layer thickness and many morphological parameters. To address the lack of no commercially available solution for TEER on Organ-on-a-Chips, we developed a measurement apparatus to investigate epithelium cultured in a commercially available organ-on-a-chip platform. Up to 96 tubules cultured in a single OrganoPlate^® have been studied by monitoring the diffusion of fluorescent probes (e.g. FITC-dextran) out of such tubes over time and calculating the apparent permeability (P_app). Here we investigate the relationship between TEER values measured using the OrganoTEER and P_app values determined using fluorescence based barrier integrity assays. We demonstrate the dynamic range for our TEER measurement method on epithelial tubes (CACO-2) including the response to toxicant exposure in comparison with Papp.

The developed system makes use of an electrode interface compatible with the OrganoPlate 3-lane. Pairs are immersed in the wells connected to the inlet and outlet wells of each chip on the OrganoPlate. TEER values can be determined for up to 80 perfused tubules within 60 seconds. The instrument can be placed within an incubator to enable automated long term monitoring of TEER over the entire duration of an epithelial/endothelial study. Collagen I at 4mg/ml was layered in the gel compartment using Phaseguide technology. Caco2 tubules were formed  against collagen I and under rocker-based perfusion flow. After 5 days of culture, we exposed to Staurosporine at varying concentrations (10uM, 2.5uM, 625uM, 156nM, 39nM, 9.7nM and 0nM). To investigate the relation between TEER and barrier integrity, we measured TEER on all tubules. We subsequently perfused them with a fluorescently labelled 10kDa Dextran dye and recorded its diffusion into the ECM channel using live fluorescent imaging. The results are expressed as TEER (fold change from before exposure) and P_app (cm.s^-1) respectively. As a result of staurosporine toxicant effect the P_app starts to increase at 20h exposures to 625nM staurosporine and higher (2.15e-5 +-0.79e-5 cm.s ^-1  at 62nM), while TEER values was already decreasing relative to control at much lower dose and exposure times (relative change of 0.78+-0.09 at 156nM and 1 hour of exposure time, 0.38+-0.06 at 9.7nM and 20 h of exposure time). The increased sensitivity of this system is combined with the possibility to program label-free measurements throughout incubation without interruption of the experiment.

We demonstrated the implementation of TEER measurements on an Organ-on-a-Chip platform and compared it to live imaging based permeability measurements. Based on these results, we propose this system for the study of healthy and damaged models of 3D barrier tissues in a non-invasive way to provides a valuable tool for drug toxicity and transport studies in Organ-on-a-Chip models.