Cytotoxicity of silica micro/nano particles with amine surface modifications to 6-3 murine microglial cell line

Silica nanoparticles (SiNPs) are widely used in biomedical applications, yet their neurotoxicity and underlying mechanisms remain vaguely understood. Microglia, the resident immune cells of the brain, play a central role in responding to exogenous particles, making them an important target for nanoparticle safety assessment. Here, we investigated the uptake and cytotoxicity of silica particles with distinct sizes and surface properties, including 3 μm-plain, 50 nm-plain, and 50 nm-NH₂, using 6-3 microglial cells derived from mouse neonates. All particle types were internalized, but only 50 nm-plain SiNPs induced severe cytotoxicity, killing approximately 80% of cells. Mechanistically, these nanoparticles entered microglia mainly through clathrin-mediated endocytosis, which triggered lysosomal swelling, lysosomal membrane permeabilization (LMP), and cathepsin-dependent cell death. In contrast, 3 μm-plain particles were incorporated via phagocytosis without overt toxicity, and 50 nm-NH₂ particles maintained viability comparable to untreated controls, with no detectable cytotoxicity. Notably, inhibition of clathrin-mediated endocytosis or cathepsin activity significantly attenuated cell death, underscoring lysosomal dysfunction as a pivotal event in SiNP-induced microglial toxicity. These findings identify lysosomal membrane destabilization as a key mechanism of SiNP-induced microglial cytotoxicity and suggest that amino surface modification may represent a useful strategy for designing safer neurocompatible SiNPs. Our results provide critical insights into nanoparticle-microglia interactions, with implications for the safe design of silica-based nanomaterials for targeted delivery of therapeutic drugs into the brain.