Comprehensive Toxicity Assessment of PEGylated Magnetic Nanoparticles for in vivo applications.

Magnetic nanoparticles (MNPs) represent one of the greatest promises for the development of a new generation of diagnostic agents for magnetic resonance imaging, with improved specificity and safety. Indeed, during the last decade the number of studies published in this field has grown exponentially. However, the clinical translation achieved so far has been very limited. This situation is likely related to the fact that most studies are focused on the in vitro characterization of these new nanomaterials, and very few provide an exhaustive in vivo characterization, where key aspects, such as pharmacokinetics, bioavailability, and, most importantly, toxicity, are properly evaluated. In this work, we propose a protocol for the comprehensive assessment of the toxicity of MNPs, based on the use of zebrafish embryos as an intermediate screening step between cell culture assays and studies in rodents. MNPs with different cores, ferrite and manganese ferrite oxide, and sizes between 3 and 20 nm, were evaluated. Cell viability at a concentration of 50 μg/mL of PEGylated MNPs was above 90 % in all cases. However, the exposure of zebrafish embryos to manganese based MNPs at concentrations above 100 μg/mL showed a low survival rate (<50 %). In contrast, no mortality (survival rate ∼100 %) and normal hatching rate were obtained for the iron oxide MNPs. Based on these results, together with the physicochemical and magnetic properties (r2 = 153.6 mM-1·s-1), the PEGylated 20 nm cubic shape iron oxide MNPs were selected and tested in mice, showing very good MRI contrast and, as expected, absence of toxicity.