Biosynthesis of magnetic nanoparticles from nano-degradation products revealed in human stem cells

Significance
Naturally occurring magnetic nanoparticles have been detected in human cells; however, their origin and role remain unknown. In the present paper, the observation of long-term transformations of man-made magnetic nanoparticles internalized in human stem cells displays a mechanism regarding their assimilation. Indeed, the nanoparticles are first degraded by the stem cells, and then new magnetic nanoparticles are synthesized in situ from the released iron. This “remagnetization” phenomenon is observed under specific pathways only, involves the ferritin protein, and seems linked to a detoxification mechanism in case of iron excess. It also brings a direct experimental proof that magnetic nanoparticles can be synthesized by human cells.