Efflux transporters and tight junction expression changes in human gastrointestinal cell lines cultured in defined medium vs serum supplemented medium

Rethinking of TEER measurement reporting for epithelial cells grown on permeable inserts

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·cm2. 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.

Proliferation and Differentiation of Intestinal Caco-2 Cells Are Maintained in Culture with Human Platelet Lysate Instead of Fetal Calf Serum

Cell lines are widely used as in vitro model systems and substitute for animal experiments. The frequently used Caco-2 cell line is considered to reflect characteristics of differentiated intestinal epithelium. However, the need to culture the cells with fetal calf serum (FCS) induces a high variability, risk of contamination and is ethically disputed. We tested the culture of Caco-2 cells with human platelet lysate (PL) instead of FCS. We compared cell viability and differentiation by measuring ATP levels, gene and protein expression of specific markers in total cell extracts, brush border membrane vesicles (BBM) and lipid rafts (LR). Cell viability was slightly enhanced in cells grown with PL compared to FCS. The cells differentiated to an intestinal phenotype like the cells cultured in FCS, as indicated by the similar gene expression levels of hexose and protein transport proteins and the structural protein VILLIN. BBM showed a comparable distribution of the intestinal hydrolases, indicating a maintained cell membrane polarity. The distribution of the marker protein FLOTILLIN-2 in LR was also similar. We conclude that PL is an exquisite and suitable replacement for FCS in the culture of Caco-2 cells that can eliminate many disadvantages incurred due to the use of FCS.