[Safety studies of nanomaterials about intracellular distribution and genotoxicity]

Recently, nanomaterials (NMs) showing useful properties such as controlled release and tissue permeability have been developed for practical use as medicine and cosmetics. On the other hand, because NMs possess innovative properties, kinetics, and biological effects distinct from those of micro size bulk materials, the potential harmful effects of NMs on humans are raising concerns about their safety. Therefore, there is an urgent need for risk assessment of NMs. To achieve this, it is most important to analyze the relationship between physicochemical properties such as particle size and surface characteristics, cellular distribution and biological effects, allowing prediction and avoidance of risk in using NMs. However there is little information about association of nanomaterial properties with kinetics (exposure, absorption, distribution, and excretion). In this respect, we have not only collected hazard information on NMs but have also analyzed the linkage between silica particle size and their hazards. We have demonstrated that NM with a diameter of under 100 nm can penetrate the stratum corneum of mouse skin and are taken up by living cells such as keratinocytes and Langerhans cells. Additionally, NM taken up by cells entered the nucleus, indicating the risk of genotoxicity. In this review, we would like to discuss the relationship between particle size, intracellular distribution, and hazard effect.