Aims: The rapidly growing industrial and medical use of nanomaterials, especially zinc oxide and titanium dioxide, has led to growing concerns about their toxicity. Accordingly, the intrinsic genotoxic and cytotoxic potential of these nanoparticles have been evaluated. Materials & methods: Using a HEp-2 cell line, cytotoxicity was tested along with mitochondrial activity and neutral red uptake assays. The genotoxic potential was determined using the Comet and the cytokinesis-blocked micronucleus assays. In addition, tyrosine phosphorylation events were investigated. Results & conclusion: We found concentration- and time-dependent cytotoxicity and an increase in DNA and cytogenetic damage with increasing nanoparticle concentrations. Mainly for zinc oxide, genotoxicity was clearly associated with an increase in tyrosine phosphorylation. Our results suggest that both types of nanoparticles can be genotoxic over a range of concentrations without being cytotoxic.

The present study has examined the effects of ZnO and TiO 2 nanoparticles (40Á70 nm range) in the presence and absence of UVA light in human sperm and human lymphocytes in the dark (D), after pre-irradiation with UV (PI) and simultaneous irradiation with UV (SI). For both ZnO and TiO 2 nanoparticles, the percentage reduction in head DNA was greater for PI and SI samples compared with samples treated in the dark. However with regard to photogenotoxicity, sperm exhibited no significant differences when the results for PI and SI and the dark were compared, except at the lowest concentration for SI samples in the case of ZnO and the lowest concentration for PI in the case of TiO 2 . However for lymphocytes, responses were statistically significant at the highest concentration for both PI and SI samples. Thus, these studies suggest that there are photogenotoxic events in these cells in the absence of overt toxicity.

Little is known of the effects of nanoparticles in human systems, let alone in diseased individuals and nanotechnology has preceded nanotoxicology. Therefore, the effects of titanium dioxide (TiO2) nanoparticles in peripheral blood lymphocytes from patients with respiratory diseases [lung cancer, chronic obstructive pulmonary disease (COPD) and asthma] were compared with those in healthy Individuals, to determine differences in sensitivity to nanochemical insult. The Comet assay was performed according to recommended guidelines. The micronucleus assay and ras oncoprotein detection were conducted according to published standard methods. The results showed statistically significant concentration-dependent genotoxic effects of TiO2 NPs in both respiratory patient and control groups in the Comet assay. The TiO2 NPs caused DNA damage in a concentration dependent manner in both groups (respiratory and healthy controls) with the exception of the lowest TiO2 concentration (10 μg/ml) which did not induce significant damage in healthy controls (n.s). When OTM data were used to compare the whole patient group and the control group, the patient group had more DNA damage (p > 0.001) with the exception of 10 μg/ml of TiO2 that caused less significant damage to patient lymphocytes (p < 0.05). Similarly, there was an increase in the pattern of cytogenetic damage measured in the MN assay without statistical significance except when compared to the negative control of healthy individuals. Furthermore, when modulation of ras p21 expression was investigated, regardless of TiO2 treatment, only lung cancer and COPD patients expressed measurable ras p21 levels. Results were achieved in the absence of cytotoxicity.

The micronucleus assay was conducted according to Fenech (2000). • Ras p21 oncoprotein level detection was performed according to Anderson et al (1998b).