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Data on the toxicological properties of zinc oxide nanoparticles (ZnO-NPs) is incomplete. ZnO-NPs may enter humans via inhalation or ingestion. The aim of the current study was to evaluate ZnO-NP-induced genotoxicity in three-dimensional (3D) mini organ cultures (MOCs) of human nasal mucosa following repeated exposure to ZnO-NP and regeneration. Nasal MOCs of 10 patients and ZnO-NPs were cultivated for one week and then characterized by electron microscopy. Nasal MOCs were partially covered by ciliated epithelium after one week of cultivation. ZnO-NPs were distributed to the cytoplasm and the nucleus. MOCs were exposed once, twice, or three times to 0.1 or 5 μg/ml of ZnO-NPs for 1 hr per exposure and were then evaluated for cytotoxicity and genotoxicity. MOCs were cultivated for 24 hr after the triple ZnO-NP exposure to allow for regeneration. ZnO-NP exposure did not result in significant cytotoxicity or apoptosis, as determined by trypan blue exclusion and caspase-3 activity, respectively. A significant increase in DNA damage was detected following repetitive exposure compared to single exposure to ZnO-NPs at 5 μg/ml, but not 0.1 μg/ml ZnO-NPs. At both concentrations of ZnO-NP, DNA fragmentation increased after 24 hr of regeneration. In contrast, DNA damage which was induced by the positive control, methyl methanesulfonate, was significantly reduced after 24-hr regeneration. Thus, our results suggest that repetitive exposure to low concentrations of ZnO-NPs results in persistent or ongoing DNA damage.

Industrial application of titanium dioxide nanoparticles (TiO(2) -NPs) as an additive in pharmaceutical and cosmetic products is increasing. However, the knowledge about the toxicity of this material is still incomplete and data concerning health and environmental safety and results of recent studies on TiO(2) nanotoxicology are inconsistent. The in vitro geno- and cytotoxicity of TiO(2) -NPs in the anatase crystal phase was evaluated in human peripheral blood lymphocytes from 10 male donors. Initially, transmission electron microscopy (TEM) was performed to describe particle morphology and size, the degree of particle aggregation, and the intracellular distribution. Cells were exposed to nanoparticles in increasing concentrations of 20, 50, 100, and 200 μg/ml for 24 hr. Cytotoxic effects were analyzed by trypan blue exclusion test and the single-cell microgel electrophoresis (comet) assay was applied to detect DNA double-strand breakage. TiO(2) -NPs were sphere shaped with a diameter of 15-30 nm. Despite dispersive pretreatment, a strong tendency to form aggregates was observed. Particles were detected in the cytoplasm of lymphocytes, but also a transfer into the nucleus was seen. The trypan blue exclusion test did not show any decrease in lymphocyte viability, and there was no evidence of genotoxicity in the comet assay for any of the tested concentrations. In conclusion, TiO(2) -NPs reached the cytoplasm as well as the nucleus and did not induce cyto- or genotoxic effects in human peripheral blood lymphocytes. Complement investigations on different human cell systems will be performed to estimate the biocompatibility of TiO(2) -NPs. Environ. Mol. Mutagen.