The effect of static magnetic fields on the aggregation and cytotoxicity of magnetic nanoparticles

Biomedical applications of magnetic nanoparticles (MNP), including superparamagnetic nanoparticles, have expanded dramatically in recent years. Systematic and standardized cytotoxicity assessment to ensure the biosafety and biocompatibility of those applications is compulsory. We investigated whether exposure to static magnetic field (SMF) from e.g. magnetic resonance imaging (MRI) could affect the cytotoxicity of superparamagnetic iron oxide (SPIO) nanoparticles using mouse hepatocytes and ferucarbotran, a liver-selective MRI contrast agent as a model system. We show that while the SPIO satisfied the conventional cytotoxicity assessment, clinical doses combined with SMF exposure exerts synergistic adverse effects such as reduced cell viability, apoptosis, and cell cycle aberrations on hepatocytes in vitro and in vivo. Concomitant treatments with the SPIO and SMF generated SPIO aggregates, which demonstrated enhanced cellular uptake, was sufficient to induce the cytotoxicity without further SMF, emphasizing that the SPIO aggregates were the predominant source of the cytotoxicity. Interestingly, the apoptotic effect was dependent on levels of reactive oxygen species (ROS) and SPIO uptake while the reduced cell viability was independent of these factors. Moreover, long-term monitoring showed a significant increase in multinuclear giant cells in the cells concomitantly treated with the SPIO and SMF compared with the control. The results demonstrate that the SPIO produces unidentified cytotoxicity on liver in the presence of SMF and the SPIO aggregates predominantly exert the effect. Since aggregation of MNP in biological milieu in the presence of strong SMF is inevitable, a fundamentally different approach to surface fabrication is essential to increase the biocompatibility of MNP.