The cytotoxicity of polycationic iron oxide nanoparticles: Common endpoint assays and alternative approaches for improved understanding of cellular response mechanism

Successful particle synthesis and coating were characterised using FTIR, PCS, TEM and ICP. The particle size from TEM was 30 nm (？16.9 mV) which increased to 40 nm (+55.6 mV) upon coating with PEI and subsequently 50 nm (+31.2 mV) with PEG coating. Both particles showed excellent stability not only at neutral pH but also in acidic environment of pH 4.6 in the presence of sodium citrate. The higher surface charge MNP-PEI resulted in increased cytotoxic effect and ROS production on all cell lines compared with the MNP-PEI-PEG. In general the effect on the cell membrane integrity was observed only in SH-SY5Y and MCF-7 cells by MNP-PEI determined by LDH leakage and LPO production. AFM topography images showed consistently that both the highly charged MNP-PEI and the less charged MNP-PEI-PEG caused cell morphology changes possibly due to membrane disruption and cytoskeleton remodelling.Our findings indicate that common in vitro cell endpoint assays do not give detailed and complete information on cellular state and it is essential to explore novel approaches and carry out more in-depth studies to elucidate cellular response mechanism to magnetic nanoparticles.Recently magnetic nanoparticles have become the focus of scientific interest due to their vast biomedical applications [1-3]. The solution instability and toxicity of iron oxide nanoparticles have been extensively studied and overcome by complete coating of the particles using materials such as silica [4], polymers [5], inorganic metals [6], bioactive molecules [7] etc. After coating the MNP core the acute toxicity experienced is attributed to the physicochemical properties of the particle surface [8]. Such properties include hydrodynamic radius [9], surface charge [10] and inherent toxicity of the coating materials [11]. However, little is known of the mechanism of cellular interaction and the long term stability of these particles in physiological conditions [12]. Cellular fate is dependent on cellular responses t