Fluorescein leakage test: a useful tool in ocular safety assessment

The fluorescein leakage test (FLT) provides information on the effects of xenobiotics on the impermeability (gate function) of epithelial cell monolayers, and their recovery after exposure. The aim of this study was to assess the validity of this test in the ocular safety assessment of surfactant-based products with various irritant potencies. Madin-Darby canine kidney cells were grown to confluency on microporous membranes and exposed for 15 min to increasing concentrations of test substances. Damage was evaluated by measuring the amount of Na-fluorescein that passed through the monolayer in 30 min, starting just after exposure. Recovery was assessed 4, 24, 48 and 72 hr later. For each sample and each time point, the amounts of test substance that produced 10% and 20% leakage (FL(10) and FL(20)) compared with a cell-free control were calculated. For the 43 samples, FL(20) values ranged from 0.65 to 1000 mg/ml. These values increased or decreased with time according to the substance. In particular, cell monolayers showed very different recoveries after exposure to anionic and cationic substances with similar initial FL(20) values. These in vitro data correlated well with historical Draize in vivo test data (Spearman's varrho > 0.90). The FLT is therefore useful as a complement to other in vitro methods for the ocular safety evaluation of cosmetics.