Abstract
Silver nanoparticles (AgNPs) are increasingly used in combination with biomaterials, such as bone grafts, to provide antimicrobial properties. Our research focused on the cytotoxic and intracellular uptake mechanism of AgNPs on osteogenic cells, and the affected gene expression of osteoblasts exposed to AgNPs. Osteoblast cells were found to be relatively resistant to AgNP exposure, compared to osteoclasts, with a higher IC50 and fewer adverse morphological features. AgNPs were endocytosed within lysosomes, which resulted in the secondary internal formation of curved AgO nano-chains assemblies within the cytosol. Furthermore, osteoblasts demonstrated an oxidative stress response, with autophagic cell death mechanisms, as indicated from qRT2-PCR analysis, with sustained upregulation of the protective gene Heme Oxygenase 1 reaching 86-fold by 48 hours (10 μg/mL). The internalization and fate of AgNPs in osteogenic cells, and the resulting impact on gene expression over time provide further understanding of the nanotoxicity mechanism of AgNPs.
AgNPs in osteogenic cells are processed via endocytosis from the cell membrane into lysosomes which degrade and aggregate the AgNPs (1). The degraded NPs form secondary nanoparticle assemblies that are templated by the lysosomal structures into discrete chains (2), and which are visible when osmium tetroxide staining is not used during initial sample preparation. The toxic effects of the intracellular AgNPs/Ag+ and reactive oxygen species were mediated at non-lethal concentrations by increased expression of HMOX1 (3). At lethal AgNP concentrations, the HMOX1 gene acted as a gateway gene (4) to further genomic responses involved in ROS mitigation, and inflammatory responses (5). [Display omitted]