The Hen's Egg Test for Micronucleus-Induction (HETMN): Validation data set.

The classical in vitro genotoxicity test battery is known to be sensitive for indicating genotoxicity. However, a high rate of 'misleading positives' was reported when three assays were combined as required by several legislations. Despite the recent optimizations of the standard in vitro tests, two gaps could hardly be addressed with assays based on 2D monolayer cell cultures: the route of exposure and a relevant intrinsic metabolic capacity to transform pro-mutagens into reactive metabolites. Following these considerations, fertilized chicken eggs have been introduced into genotoxicity testing and were combined with a classical read-out parameter, the micronucleus frequency in circulating erythrocytes, to develop the hen's egg test for micronucleus induction (HET-MN). As a major advantage, the test mirrors the systemic availability of compounds after oral exposure by reflecting certain steps of ADME (Absorption, Distribution, Metabolism, Excretion) without being considered as an animal experiment. The assay is supposed to add to a toolbox of assays to follow up on positive findings from initial testing with classical in vitro assays. We here report on a validation exercise, in which more than 30 chemicals were tested double blinded in three laboratories. The specificity and sensitivity of the HET-MN were calculated to be 98% and 84%, respectively, corresponding to an overall accuracy of 91%. A detailed protocol, which includes a picture atlas detailing the cell and micronuclei analysis, is published in parallel (1).