Development of a method for assessing micronucleus induction in a 3D human skin model (EpiDerm)

To meet the requirements of the EU 7th Amendment to the Cosmetics Directive, manufacturers of cosmetics products will need to ascertain the safety of ingredients using non-animal methods. Starting in 2009, in vivo genotoxicity tests for cosmetics ingredients will not be allowed. Skin is a target area of interest for many cosmetic products because of its relatively high exposure. Therefore, it would be beneficial to have a non-animal, skin-based genotoxicity assay, especially one that utilized human skin in vitro. In this paper, we describe the development of a reproducible micronucleus assay that uses EpiDerm engineered human skin constructs (MatTek Corp., Ashland, MA). We describe methods for isolating single cells from the 3D skin model and for processing the cells for microscopic analysis of micronuclei (MN). In addition, since little was known about the kinetics of the dividing keratinocytes in the EpiDerm model, we evaluated whether cytochalasin B (Cyt-B) could be used to distinguish the population of dividing cells allowing the development of a micronucleus assay in binucleated cells. We found that the frequency of binucleated cells increased both with time and with increasing concentration of Cyt-B. After a 48-h exposure, 30-50% binucleated cells were reproducibly obtained. Finally, we evaluated micronucleus induction using the model genotoxicants mitomycin C (MMC) and vinblastine sulfate (VB). The background frequency of MN is very low and reproducible in this model, and statistically significant increases in the frequency of micronucleated cells were induced by both MMC and VB. These are initial steps in developing a routine "in vivo-like" assay for chromosomal damage in human tissue. It is hoped that other investigators utilize these methods to further the understanding of this potentially valuable new non-animal method.