Owing to the increasing development of nanotechnology, there is a need to assess how engineered nanomaterials can interact with living cells. The main purpose of the present study was to assess whether metal cobalt nanoparticles (CoNP 100-500 nm) are genotoxic compared to cobalt ions (Co(2+)). Uptake experiments were carried out by incubating peripheral blood leukocytes (PBLs) with (57)Co(2+) (added to stable Co(2+) 10(-2) M to obtain concentrations in the range of 10(-5) to 10(-4) M) or with (60)CoNP for 24 and 48 h. Whereas intracellular Co(2+) showed slight or no variations over the baseline levels, CoNP were taken up efficiently leading to intracellular CoNP concentrations of 485 +/- 106.1 and 970 +/- 99 fg per cell after 24 and 48 h, respectively. The genotoxicity end points considered in this study were the frequency of binucleated micronucleated (BNMN) cells and the percentage of tail DNA (% Tail DNA) fragmentation by means of the comet assay. Genotoxic effects were evaluated by incubating PBLs of three healthy donors with subtoxic concentrations (10(-5) to 8 x 10(-5)M) of Co(2+) in the form of cobalt chloride, CoNP and 'washed' CoNP, the latter to exclude any interference by Co(2+). On a group basis, Co(2+) induced a clear trend in the increase of the BNMN frequency, whereas CoNP showed only minor changes. Moreover, we observed a high variability among donors in the induction of micronuclei. The comet assay showed a statistically significant dose-related increase in % Tail DNA for CoNP (P < 0,001), whereas Co(2+) did not induce significant changes over control values. These findings suggest that nanosized Co can be internalized by human leukocytes and can interact with DNA leading to the observed genotoxic effects, which are, however, modulated both by donor's characteristics and/or by Co(2+) release.
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