Lucifer Yellow (50 μM) was added as a control of barrier integrity (Papp < 17•10 -6 cm/s). To perform the assay, 500 µL of the compound in Ringer HEPES was added to the donor compartment and 1500 µL of Ringer HEPES was introduced into the acceptor compartment. The plates were incubated for 2 h at 37 ºC, and the solutions from both compartments were recovered and analysed. The samples were evaluated in triplicates. The amount of protein conjugates was quantified by fluorescence with Fluorescence Spectrophotometer F2500 HITACHI. The selected slit for excitation and emission was 5 nm and 10 nm, respectively. The voltage for the detector was 700 V. Apparent permeability was calculated with the following formula: