Release of metals and dissolution of mineral fibres in THP1 macrophagic cell-line systems exposed to chrysotile asbestos. A synchrotron-based study

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In chrysotile, the most commercialized asbestos species, Fe and other metals are worth considering in its potential toxicity (Gualtieri et al., 2019); in fact, large amounts of Fe (>1000 ppm) and trace metals (Cr, Ni, Co, Mn, etc.) are also intimately associated with the raw material. Since both Fe and trace metals are usually isomorphous substituent of Mg in octahedral sites, their release into the lung environment is strictly connected to that of Mg, when fibres are dissolved by the macrophage phagocytosis (Pollastri et al., 2015). Thus, trace elements are potentially involved in the production of reactive oxygen species (ROS), in addition to Fe (Bloise et al., 2016). In the frame of the PRIN 2017 3X8WA4 project, THP1-cells exposed to chrysotile fibres (from Balangero, Italy) showed the formation of aggregated structures of both fibrous and non-fibrous species, including Fe oxides and sulphides. These clusters have been extensively characterized by micro-Raman analysis but potential dissolution mechanism needs further investigation, looking at the spatial distribution of metals in the biological system and to the molecular structure of the existing species. To this extent, synchrotron-based X-ray imaging and spectroscopy represent an emerging and effective tool for investigating biological systems at the sub-cellular level, able to clarify metals mobilization mechanism, highlighting both their intracellular spatial distribution and the changes in their valence state induced by the fibres-cells interaction (Cammisuli et al., 2018). A combined approach with AFM and X-ray fluorescence (XRF) elemental mapping with a sub-micrometre resolution, performed respectively at the at the NanoInnovation lab and the TwinMic beamline of the Italian Elettra Synchrotron Facility in Trieste, has been applied on THP-1 cells after different exposure time to fibers (8 h, 24 h, 96 h). On the same samples, at the ID21 beamline (ESRF, Grenoble, France), micro-XANES at the Fe K-edge provided fundamental details about the chemical states of Fe and the potential transformations of Fe sulphides/oxides in the organic environment. Micro-XANES at the Cr Kedge elucidated the possible Cr toxicity, discriminating Cr(III) - from the asbestos fibres - and potential Cr(VI) - as intracellular toxic species. Results have been compared with those obtained with oxidative stress analysis, genotoxic and DNA damage investigations, cellular toxicity and viability tests. The whole study represents an important step forward in understanding the mechanisms of toxicity/pathogenicity of asbestos with particular emphasis on the role of iron Fe and other toxic metals released during the dissolution processes induced by phagocytosis.

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