Although magnetic nanoparticles are increasingly used in cell imaging and tissue bioengineering, their long-term fate in stem cells remains unknown. Researchers from CNRS, Sorbonne University, and Paris Diderot and Paris 13 universities have shown significant degradation of these nanoparticles, followed in some cases by “re-magnetizing” cells. This phenomenon is the sign of a biosynthesis of new magnetic nanoparticles from iron released into the intracellular medium by the degradation of the first nanoparticles. Posted in PNAS on February 11, 2019, this work could explain the presence of a “natural” magnetism in human cells, and help us to consider new tools for nanomedicine, thanks to this magnetism produced by the cells themselves.
Magnetic nanoparticles are at the heart of today’s nanomedicine: they serve as diagnostic imaging agents, thermal anticancer agents, drug targeting agents and tissue engineering agents. The question of their fate in cells, after they had accomplished their therapeutic mission, was not well understood.
To follow the path of these nanoparticles in cells, researchers from the Matière et Systèmes Complexes Laboratory (CNRS / Université Paris Diderot) and the Vascular Translational Research Laboratory (INSERM / Université Paris Diderot / Université Paris 13), in collaboration with scientists de la Sorbonne The University has developed an original approach to nanomagnetism in living organisms: first, it incorporated magnetic nanoparticles in vitro into human stem cells. They then let them differentiate and develop for a month, observe them long-term in the intracellular environment, and follow their transformations.
By following the “magnetic imprint” of these nanoparticles in cells, the researchers showed that they were first destroyed (cell magnetization drops) and released iron into the intracellular environment. Then, this “free” iron was stored in non-magnetic form in ferritin, the protein responsible for iron storage, or served as the basis for the biosynthesis of new magnetic nanoparticles within the cell.
This phenomenon is known to occur in some bacteria, but such biosynthesis has never been demonstrated in mammalian cells. This could explain the presence of magnetic crystals in humans, seen in cells of various organs, including the brain. What is more, this storage of iron in magnetic form could also be a way for the cell to “detoxify” itself in the long term to counter excess iron. From the point of view of nanomedicine, this biosynthesis opens a new path towards the possibility of purely biological magnetic labeling in cells.