Assessing the toxicity of metal ions and nanoparticles
NPs have revolutionised the functionalities of products and devices in nearly every sector of the economy. Their potential release into the environment during production, use and disposal requires careful consideration of risks and toxicity. The EU-funded NADETOX (Nanomics in vitro developmental toxicology) project focused on Co and gold (Au) NPs that are applied in cancer therapy. The use of a promising and attractive alternative in vitro testing method based on the 3Rs (Reduction, Refinement, Replacement of animal tests) approach was a pillar of the research programme. Scientists exploited FETAX (Frog Embryo Teratogenesis Assay-Xenopus), a well-established bioassay developed in the 1980s. FETAX is a powerful, flexible and cheap assay allowing the rapid (over a few days) evaluation of the effects of chemicals on the embryonic growth in Xenopus laevis. The team started by evaluating impurities in the metallic NPs that could confound interpretation of results, undermining scientific validity. Instrumental and Radiochemical Neutron Activation Analysis (INAA and RNAA, respectively) as well as ICPMS (Inductively coupled plasma mass spectrometry) analysis was carried out. The Co-NPs were found to have very low levels of elemental impurities in contrast to the Au-NPs. Only the Co-NPs were used in subsequent tests. Moreover, the staff carried out TEM (Transmission Electron Microscopy) analysis in order to evaluate potential effects of neutron irradiation on the structure of NPs. TEM suggested that neither the surface nor size of metal NPs were affected. Researchers then employed INAA, RNAA and ICPMS to study also the baseline elemental composition of Xenopus larvae. The uptake of CO2+ and Co-NPs was studied according to FETAX protocol. Co was taken up by embryos in both forms used. Moreover, Co was shown to bind DNA; this could affect gene expression, as suggested by preliminary DD-PCR (Differential Display-Polymerase Chain Reaction) experiments. NADETOX has added an important piece to the puzzle of whether or not metallic NPs commonly used in consumer products can have toxic effects. Further work should increase the safety of handling and manufacture of both NPs and the products that rely on them for improved function.
