Elsevier

Biomaterials

Volume 32, Issue 16, June 2011, Pages 3988-3999
Biomaterials

Long term in vivo biotransformation of iron oxide nanoparticles

https://doi.org/10.1016/j.biomaterials.2011.02.031Get rights and content

Abstract

The long term outcome of nanoparticles in the organism is one of the most important concerns raised by the development of nanotechnology and nanomedicine. Little is known on the way taken by cells to process and degrade nanoparticles over time. In this context, iron oxide superparamagnetic nanoparticles benefit from a privileged status, because they show a very good tolerance profile, allowing their clinical use for MRI diagnosis. It is generally assumed that the specialized metabolism which regulates iron in the organism can also handle iron oxide nanoparticles. However the biotransformation of iron oxide nanoparticles is still not elucidated. Here we propose a multiscale approach to study the fate of nanomagnets in the organism. Ferromagnetic resonance and SQUID magnetization measurements are used to quantify iron oxide nanoparticles and follow the evolution of their magnetic properties. A nanoscale structural analysis by electron microscopy complements the magnetic follow-up of nanoparticles injected to mice. We evidence the biotransformation of superparamagnetic maghemite nanoparticles into poorly-magnetic iron species probably stored into ferritin proteins over a period of three months. A putative mechanism is proposed for the biotransformation of iron-oxide nanoparticles.

Introduction

The long term outcome of nanoparticles (NPs) in the body is a major concern, which has been raised by the recent development of nanotechnology and nanomedicine. How nanomaterials interact with living constituents and are processed by the organism are justifiably the most-asked questions whenever an application of nanomaterials is proposed [1]. Safety issues are becoming prominent in the development of new nanodevices, especially in the biomedical field. Inorganic nanoparticles that exhibit unique optical or magnetic properties are of special interest for diagnosis and therapeutic applications exploiting their response to physical, remotely activated, stimuli [2], [3]. However, while tremendous advances have been made in the tuning of the chemical and physical hallmarks of NPs, their fate once injected in the organism is still not controlled. In particular, the transformations induced by cellular activity on inorganic nanoparticles are largely unknown yet.

Most studies carry out in vitro assessments of NPs toxicity using cellular models [1], [4], [5], [6]. They point out some critical parameters governing the biological response to nanomaterials, such as their size, composition, surface reactivity, architecture, stability with respect to the biological medium and intracellular distribution. However, such studies always require validation in vivo, where most of these parameters are no longer controlled. Hence reliable methods are eminently desirable to monitor the fate of inorganic nanoparticles directly in the organism.

One approach to assess the in vivo behaviour of inorganic nanoparticles is to rely on their most salient properties, their physical properties, which precisely make their interest for applications. For example, optical properties of plasmonic or luminescent nanoparticles can be exploited to study their biodistribution [7]. Similarly, magnetic properties of iron oxide NPs enable their follow-up by MRI, a particularly attractive non-invasive imaging technique, paving the way of many diagnostic applications [8]. However a quantitative relationship between the physical signal and the amount of nanoparticles is often compromised, because the physical properties may be impacted by the biological environment or by the peculiar organization adopted by nanomaterials when immerged in the blood flow or processed by cells [9]. It is particularly true for MRI which relies on the indirect effect of the magnetic field produced by nanoparticles on the dynamics of surrounding protons [10]. Therefore a reliable monitoring of nanoparticles should be based on their specific physical properties, independently of their environment.

Here we propose to refer on the superparamagnetic properties of nanomagnets to monitor their fate in vivo. We perform complementary techniques of nanomagnetism in order to specifically quantify iron oxide NPs based on their magnetic moment and to assess their degradation and biotransformation over time. The progressive modification and loss of their characteristic magnetic properties are interpreted as the signatures of the transformations operated by cells on nanoparticles. Because the degradation obviously occurs at a nanometer scale, the magnetic follow-up is here complemented by a nanoscale structural characterization of the intracellular outcome of nanoparticles. Our multiscale approach, to evaluate biologically-induced changes of the nanoparticle state, applies here to iron oxide NPs used as MRI contrast agent. Although iron-based NPs have never shown acute or sub-acute toxicities, the way they are handled by the iron metabolism is still not elucidated [11], [12], [13], [14]. The present results are thus directly relevant to current safety considerations in clinical diagnostic and therapeutic uses of nanomagnets.

Section snippets

Design of the study

In this study, we aimed to assess the biodistribution and outcome of P904 nanoparticles (Guerbet SA) administrated intravenously to mice. P904 nanoparticles consist in 8 nm superparamagnetic cores of maghemite coated by hydrophilic derivatives of glucose. These nanoparticles are currently developed by Guerbet SA, as a contrast agent for non-invasive imaging of inflammation by MRI. The diagnosis and therapeutic follow-up of various pathologies involving inflammatory processes, such as

Specific quantification of superparamagnetic nanoparticles by ferromagnetic resonance

We first evaluate Ferromagnetic Resonance as a quantitative method to monitor iron oxide nanoparticles in tissues. Ferromagnetic Resonance (FMR) is a spectroscopic method to probe the dynamics of magnetization of unpaired electrons collectively coupled in a ferro- or ferrimagnetic lattice. For single domain NPs, resonance arises from the precessional motion of their global magnetic moment, which experiences the external magnetic field B0, plus the internal local fields due to anisotropy energy

Discussion

FMR and SQUID measurements were demonstrated here as accurate techniques to quantify magnetic nanoparticles in biological samples and characterize the evolution of their superparamagnetic properties in the organism. These methods, based on nanomagnetism, can specifically detect ferrimagnetic nanocrystals, which exhibit a peculiar magnetic behaviour according to their size, magnetization and magnetic anisotropy. The high sensitivity of FMR measurements allows a quantification of

Conclusion

A multiscale approach was used here to delineate the way taken by cells in vivo to process and degrade iron oxide nanoparticles over time. The three-month magnetic follow-up of nanoparticles, using ferromagnetic resonance and SQUID measurements, gave evidence of the degradation of magnetic nanocrystals through a loss of their peculiar superparamagnetic properties. At the organism level, we observed the relocation of iron species from the liver to the spleen. The nanoscale investigation using

Acknowledgement

We acknowledge Guerbet for providing us with the nanoparticles. We are grateful to Anne d’Encausse, Eric Lancelot, Sébastien Ballet, Emmanuelle Canet-Soulas, Martin Devaud and Christian Ricolleau for fruitful discussions and to Achraf Al Faraj, Sylvie Manin and Thomas Decaen for technical assistance. This work has been supported by the ANR (Agence Nationale de la Recherche) TecSan “Inflam” and by the European project Magnifyco (Contract NMP4-SL-2009-228622).

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