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Complete transformation of ZnO and CuO nanoparticles in culture medium and lymphocyte cells during toxicity testing
Ivask, A., K. Scheckel, P. Kapruwan, V. Stone, H. Yin, N. Voelcker, AND E. Lombi. Complete transformation of ZnO and CuO nanoparticles in culture medium and lymphocyte cells during toxicity testing. Nanotoxicology. Taylor & Francis Group, London, Uk, 11(2):150-156, (2017). https://doi.org/10.1080/17435390.2017.1282049
Although a number of studies have discussed the transformation of nanoparticles during toxicity testing, the extent and nature of these transformations is relatively difficult to qualitatively assess let alone to quantify. One alternative method to assess nanoparticle transformation and speciation during toxicological testing is synchrotron radiation-based X-ray absorption near edge structure (XANES) spectroscopy. XANES is capable of providing relative quantitative information about elemental speciation without prior separation of particulates and ions. The aim of this study was to reveal the speciation of nanoparticulate ZnO and CuO before and during toxicological testing. Even though the number of publications on ZnO and CuO nanoparticles and their toxicity is significant, information on dissolution and transformation of those particles in the test conditions is usually insufficient and thus judgement on which factors are driving their toxic effects is difficult. In this study, we used synchrotron radiation-based XANES and resulting K-edge Zn and Cu spectra to assess the speciation of 30 and 80 nm ZnO nanoparticles and 15 nm CuO nanoparticles in human T-lymphocyte cells and in their exposure medium over a 24 h time period, which is standard for in vitro toxicological assays. The results indicated prompt transformation of the nanoparticles in the test medium. Furthermore, speciation profiles of ZnO and CuO inside the cells overlapped with soluble Zn and Cu, respectively, suggesting that cellular transformation and sequestration of nanoparticles and their ionic counterparts were similar. This finding is significant for interpretation of past and future toxicological results of ZnO and CuO nanoparticles. This information is of interest to Regional and Program Office decision makers, States, and local affected communities.
Here, we present evidence on complete transformation of ZnO and CuO nanoparticles, which are among the most heavily studied metal oxide particles, during 24 h in vitro toxicological testing with human T-lymphocytes. Synchrotron radiation-based X-ray absorption near edge structure (XANES) spectroscopy results revealed that Zn speciation profiles of 30 nm and 80 nm ZnO nanoparticles, and ZnSO4- exposed cells were almost identical with the prevailing species being Zn-cysteine. This suggests that ZnO nanoparticles are rapidly transformed during a standard in vitro toxicological assay, and are sequestered intracellularly, analogously to soluble Zn. Complete transformation of ZnO in the test conditions was further supported by almost identical Zn spectra in medium to which ZnO nanoparticles or ZnSO4 was added. Likewise, Cu XANES spectra for CuO and CuSO4-exposed cells and cell culture media were similar. These results together with our observation on similar toxicological profiles of ZnO and soluble Zn, and CuO and soluble Cu, underline the importance of dissolution and subsequent transformation of ZnO and CuO nanoparticles during toxicological testing and provide evidence that the nano-specific effect of ZnO and CuO nanoparticulates is negligible in this system. We strongly suggest to account for this aspect when interpreting the toxicological results of ZnO and CuO nanoparticles.