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 Dra ize eye irritation test (Draize test). The cytotoxicity of thirty-eight cos metic ingredients as well as a physiological saline solution was determined on SIRC cells at five to seven laboratories. SIRC-NRU and SIRC-CVS were pe rformed according to the common standard operating procedure (SOP). The 50% effective concentration (EC50) was deter mined for each ingredient. The EC 50 Of SIRC-CVS was similar to that of SIRC-NRU, showing a strong correlatio n (r = 0.995). The coefficient of variation (CV) of EC50 which represents t he interlaboratory reproducibility of SIRC-NRU was 32.1%, whereas that of S IRC-CVS was 32.8%. The logarithmically transformed EC50 values showed a str ong 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 regres sion 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. (C) 1999 Elsevier Science Ltd. All rights reserve d.