Interlaboratory validation of the in vitro eye irritation tests for cosmetic ingredients. (8) Evaluation of cytotoxicity tests on SIRC cells.

Two common assays, the neutral red uptake assay (SIRC-NRU) and the crystal violet staining assay (SIRC-CVS), were evaluated as alternatives to the Draize eye irritation test (Draize test).The cytotoxicity of thirty-eight cosmetic ingredients as well as a physiological saline solution was determined on SIRC cells at five to seven laboratories. SIRC-NRU and SIRC-CVS were performed according to the common standard operating procedure (SOP). The 50% effective concentration (EC(50)) was determined for each ingredient. The EC(50) of SIRC-CVS was similar to that of SIRC-NRU, showing a strong correlation (r=0.995). The coefficient of variation (CV) of EC(50) which represents the interlaboratory reproducibility of SIRC-NRU was 32.1%, whereas that of SIRC-CVS was 32.8%. The logarithmically transformed EC(50) values showed a strong correlation with the maximal average Draize total score (MAS) (SIRC-NRU: r=-0.816 (n=30), SIRC-CVS: r=-0.805 (n=29)). Both methods could be applied to water-insoluble substances and dyes. However, strong acids, alkanolamines and alcohols had a tendency to deviate from the linear regression lines which were obtained from the in vivo and in vitro data for both methods in the present study. These results suggest that cytotoxicological testing on SIRC cells may provide an alternative method to the Draize test for cosmetic ingredients.