Size and surface properties of silica micro/nanoparticles are critical in modulating endocytosis-mediated cellular responses in murine RAW-Blue macrophages and N18 neuroblastoma cells

The purpose of this study was to examine the molecular mechanisms by which silica micro/nanoparticles (SiPs) with different sizes and surface functional groups cause cytotoxicity in the murine RAW-Blue macrophages and N18 neuroblastoma cells. The possibility that these materials may act via macropinocytosis, clathrin-mediated endocytosis (CME), or caveolae-mediated endocytosis (CvME) was focused. Three types of SiPs, 3 μm-plain (3 μm diameter particles without surface modification), 50 nm-plain (50 nm diameter particles without surface modification) and 50 nm-NH2 (50 nm diameter particles with an amine functional group as surface modification) were tested. Cytotoxicity in the presence of 50 nm-plain in RAW-Blue macrophages was seen but N18 neuroblastoma cells did not exhibit evident cytotoxicity in the presence of 50 nm-plain at the 24-hr time point. In the presence of 50 nm-plain, cell proliferation was significantly inhibited and cell death was significantly induced in RAW-Blue macrophages. These macrophages incorporated particles of 50 nm-plain and 50 nm-NH2 via the CME and macropinocytosis pathways. When the macrophages were treated with 50 nm-plain plus chlorpromazine, a CME inhibitor, the NF-κB-inducible secreted embryonic alkaline phosphatase (SEAP) activity significantly decreased compared to the control. When the macrophages were treated with 50 nm-plain plus imipramine, a macropinocytosis inhibitor, cell death significantly decreased compared to the control. Collectively, these results demonstrate that the size and surface properties of SiPs are critical in modulating endocytosis-mediated cellular responses including cytotoxicity and regulation of the SEAP activity; thus enhancing the safe and effective design of SiPs and a reliable standard for biomedical applications.