Silver Nanoparticles Induce a Size-dependent Neurotoxicity to SH-SY5Y Neuroblastoma Cells via Ferritinophagy-mediated Oxidative Stress

Silver nanoparticles (AgNPs) are widely used in a variety of consumer products because of their antibacterial and antifungal characteristics, but little is known about their toxicity to the brain. In this study, we investigated AgNP-induced neurotoxicity using the human neuroblastoma cancer (SH-SY5Y) cell line. After a 24 h treatment of AgNPs with two primary sizes (5 and 50 nm labeled as Ag-5 and Ag-50, respectively), a series of toxicological endpoints including cell viability, expression of proteins and genes in amyloid precursor protein (APP) amyloid hydrolysis process and ferritinophagy signaling pathways, oxidative stress, intracellular iron levels, and molecular regulators of iron metabolism were evaluated. Our results showed that both Ag-5 and Ag-50 induced notable neurotoxic effects on SH-SY5Y cells indicated by cell proliferation inhibition, increased BACE1 protein expression, and decreased APP and ADAM10 gene expression. Activation of nuclear receptor coactivator 4-mediated ferritinophagy and blockade of autophagic flux were induced by AgNPs, accompanied by intracellular iron accumulation and overexpression of divalent metal-ion transporter-1 and ferroportin1 in SH-SY5Y cells. In addition, AgNPs significantly decreased glutathione peroxidase 4 protein expression but increased malondialdehyde concentration, suggesting that AgNP-induced iron accumulation may trigger oxidative stress by disruption of the intracellular oxidant and antioxidant systems. In addition, compared with Ag-50, Ag-5 with higher cellular uptake efficiency caused more detrimental effects on SH-SY5Y cells. In conclusion, our findings demonstrated a size-dependent neurotoxicity in SH-SY5Y cells by AgNPs via ferritinophagy-mediated oxidative stress.