MEIC evaluation of acute systemic toxicity. II. In vitro results from 68 toxicity assays used to test the first 30 reference chemicals and a comparative cytotoxicity analysis

By Clemedson, C. - McFarlane-Abdulla, E. - Andersson, M. - Barile, F.A. - Calleja, M.C. - Chesne, C. - Clothier, R. - Cottin, M. - Curren, R. - Dierickx, P.

Results from tests of the first 30 MEIC reference chemicals in 68 different toxicity assays are presented as a prerequisite to subsequent in vitro/in vivo comparisons of acute toxicity data. A comparative cytotoxicity study was also carried out. Firstly, the variability of all of the results was analysed by using principal components analysis (PCA), analyses of variance (ANOVAs) and pairwise comparisons of means according to Tukey's method. The first PCA component described 80% of the variance of all of the cytotoxicity data. Tukey's ANOVA indicated a similar sensitivity for the assays, of approximately 80%. Secondly, the influence of five major methodological components on the general variability of the results was evaluated by linear regression and ANOVA linear contrast analyses. The findings were that: the toxicity of many chemicals increased with exposure time; in general, human cytotoxicity was predicted well by animal cytotoxicity tests; this prediction was poor for two chemicals; the prediction of human cytotoxicity by the ecotoxicological tests was only fairly good; one organotypic endpoint used, i.e. contractility of muscle cells, gave different results to those obtained according to viability/growth toxicity criteria; twelve comparisons of similar test systems involving different cell types (including highly differentiated cells) showed similar toxicities regardless of cell type; and nine out often comparisons of test systems with identical cell types and exposure times revealed similar toxicities, regardless of the viability or growth endpoint measurement used. Factors b, f and g must be the main causes of the remarkable similarity between the total results, while factors a, c, d and e, together with other minor factors that were not analysed, contributed to the 20% dissimilarity. The findings strongly support the basal cytotoxicity concept, and will facilitate future in vitro toxicity testing.