Differential internalization of superparamagnetic iron oxide nanoparticles in different types of cells

Superparamagnetic iron oxide nanoparticles (SPION) have attracted great attention for nanomedical applications, but the mechanisms underlying the transmembrane transport of SPION in variant cells has not been fully defined. The present study investigated the internalization of SPION in three cell models with different phagocytic capacity using transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) analyses. The EDS study aimed to further confirm if the suspected internalized particles were iron-containing SPION. SPION could be taken up quickly by macrophage-like cell line RAW264.7 (with strong phagocytic capacity) and slowly by the 3T3-L1 cells (with weak phagocytic capacity), but not by red blood cells (with no phagocytic capacity). The internalized SPION were mainly found in the cytoplasmic vesicles, with no localization in the endoplasmic reticulum, mitochondria and nucleus. We conclude that the internalization of SPION in the three types of mammalian cells was mediated by phagocytosis, not by direct membrane penetration.