(95d) A Liposome Assay for Evaluating the Ocular Toxicity of Surfactants

The ocular toxicity of various compounds is often determined by the Draize eye test, which has been criticized in the past for its lack of reproducibility and the cruelty associated with harsh testing conditions for animals. We have developed a liposome based in vitro assay for estimating ocular toxicity. The release of calcein dye from liposomes induced by interactions with surfactants was studied and correlated to Draize eye scores. First, the liposome assay was conducted for various surfactants at identical concentrations and correlated to the Draize scores. Next, mechanistic and geometric considerations were used to determine the appropriate surfactant concentration that should be used in the liposome assay. Correlations between percentage dye released and the Draize scores were drastically improved after surfactant concentrations were chosen to be CMC/200, where CMC is the critical micelle concentration. With this choice of surfactant concentration, excellent correlations were obtained with Draize scores from three separate sources and four different ocular surfactant loadings (Pearson = 0.99, 0.82, 0.78, 0.74; Spearman = 0.94, 0.79, 0.79, 0.85). Subsequently, the ocular toxicities of six non-ionic surfactants, Brij 700, Brij 58, Brij 56, Brij 78, Brij 97, and Brij 98 were shown to be minimal based on the proposed correlations. The modified liposome assay developed here could be used in combination with other in vitro assays to obtain initial estimates for ocular toxicities, thereby minimizing the need for the Draize eye test.