Neurotoxicity of four frequently used nanoparticles: a systematic review to reveal the missing data.

Systemic exposure to nanoparticles (NPs) adversely affects different organs, including the nervous system. We systematically extracted data from publication on PubMed and Embase database up to the year 2020, and analyzed in vitro and in vivo neurotoxicity of 4 of the most well studied NPs (silver NPs, carbon-based NPs, iron NPs and silica NPs). A relatively good correlation was observed between in vitro and in vivo effects, including genotoxicity, oxidative stress, apoptosis and pro-inflammatory effects. However, crucial knowledge gap exists in current understanding of the underlying mechanisms. Some of the critical knowledge gaps and research needs identified in relation to neurotoxicity of nanoparticles include (1) lack of physio-chemical characteristics of NPs used, (2) cellular/tissue uptake of NP, (3) NP translocation across the blood-brain barrier (BBB), (4) Effect of exposure routes.