Toxicity Patterns of Clinically Relevant Metal Oxide Nanoparticles

Nanostructured drugs are being approved for clinical use, although there is a serious deficit of systematic studies of these materials. Data on toxicity of nanoparticles (NPs) can vary due to different methods of preparation, size, and shape. We investigated the toxicity against cultured human cells, the acute toxicity in mice, and the influence on conjugative transfer of antibiotic resistance genes of clinically relevant NPs such as TiO₂, ZrO₂, HfO₂, Ta₂O₅, Fe₃O₄, and AlOOH. NPs were synthesized as aqueous sols by the same method in aqueous solution, with almost identical size 2-10 nm. None of these NPs was cytotoxic at concentrations compatible with water solubility. Furthermore, TiO₂, HfO₂, Ta₂O₅, Fe₃O₄, and AlOOH were not toxic to mice after oral administration. However, ZrO₂ showed rather high toxicity, with LD₅₀ 2277.8 mg/kg. Experiments with plasmid transfer between bacteria demonstrated that AlOOH NPs were the most hazardous since this material promoted the emergence of resistance to antibiotics. Thus, although our metal oxide NPs are largely non-toxic, their properties may differ in specific biological situations.