Techniques to measure BBB permeability in transwell models
The transwell insert sits in the well and has a semipermeable base that allows passage of liquid between the upper and lower reservoirs. (A) TEER measurements are taken across the endothelial cell monolayer using ‘chop stick’ electrodes. Electrical resistance increases when the BBB is more fully formed equating to a lower permeability. Tissue resistance is measured in Ω, and the normalised UAR of the BBB is measured in Ω cm2. (B) Permeability to compounds of known size can be used to assess the permeability of the BBB. Following the addition of a fluorescent or other tagged molecule to the upper chamber, the amount of the molecule appearing in the bottom chamber can be measured over time, enabling a calculation of permeability across the BBB to be calculated.