Genotoxicity of nanosized TiO2 particles in human reconstructed full thickness skin models

Due to the widely use of nanomaterials in skin care products the examination of the potential risk to human health is of a great importance. Many studies have shown that through intact rodent skin nanomaterials do not penetrate. With the aim to reduce in vivo experiments 3D human reconstructed skin models might be used for absorption and effects monitoring of chemicals. We used human reconstructed full thickness skin models (hEFT) to check for potential genotoxic hazard of manufactured nanomaterials by using the comet assay. Our hypothesis was that a fraction of small nanoparticles in polydispersed materials as investigated by the NANOGENTOX consortium might penetrate stratum corneum layer and reach viable epidermal cells. In more than hundred 3D human reconstructed full thickness skin models all TiO2 nanomaterials (NM102 - NM105) investigated for DNA damage in different doses were negative at each dose level in the Comet Assay. In contrast the chemical control MMS consistently generated significant increases in DNA-damage parameters such as percent DNA in comet tail and tail moment at the 3-h incubation time. Indices of DNA damage decreased after prolongation of incubation times, showing that this viable skin model - consisting of stratum corneum, epidermis, and dermis – has DNA repair. We postulate that nanomaterials that agglomerate resulting in realistic nanoparticle sizes above 20 nm will not enter the viable fully differentiated human skin models and consequently would not exert genotoxic effects in this test system. Our results comply with the studies with pig (Monteiro- Riviere et al., 2011) and rodent skin (Adachi et al., 2010 and Kimura et al., 2012). It is proposed that investigations of skin penetration on 3D skin models will be continued investigating exposure scenarios towards certified stably monodispersed nanomaterials of defined realistic sizes between 1 nm and 20 nm when available.