Investigating the Cytotoxic and Neurotoxic Effects of Selected Nanoparticles on RAW 264.7 Macrophages and Acetylcholinesterase Activity In Vitro

The increased production and utilization of nanoparticles (NPs) in consumer products have raised concerns about their potential impact on the environment at national and international levels as they move through different trophic levels. Previous research has shown that they possess the ability to infiltrate cellular and subcellular structures, potentially interfering with important physiological processes and leading to toxicity. Studies have also indicated that nanoparticle toxicity varies significantly with changes in physicochemical properties, even among nanoparticles with identical chemical compositions. Because of this variable toxicity potential, it has become imperative to study the toxicity of these materials on vital physiological systems on a case-by-case basis, particularly before their widespread utilization in consumer products. This study evaluated the cytotoxic effects of selected nanoparticles (i.e. AgNPs, TiO₂NPs, CD NPs, CD-Amine), with a particular emphasis on their toxicity to macrophages. The study involved exposing the immune-representative RAW 264.7 cell line to various concentrations of NPs, both with and without the presence of lipopolysaccharide (LPS). Results showed that silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO₂NPs) had an adverse impact on cell viability under both conditions. The unmodified carbon dot nanoparticles only had a moderate impact on viability. However, toxicity increased significantly when carbon dot NPs were modified with amine groups, surpassing that of metal-based NPs (i.e., AgNPs and TiO₂NPs), highlighting the critical role of surface charge in influencing cytotoxicity. Concurrently, the study also comprehensively assessed the potential neurotoxicity of these nanoparticles by measuring their modulatory potential on acetylcholinesterase (AChE) activity using Ellman's reagent. Findings indicated that both AgNPs and amine-modified carbon dots (CD-Amine) significantly inhibited AChE activity, while TiO₂NPs and CDNPs had no impact on AChE activity. Interestingly, this inhibition was not dependent on whether the nanoparticles were metal- or carbon-based, or the size of the nanoparticles, suggesting that the interaction between nanoparticles and enzymes is likely influenced by the chemistry of the enzyme and the nanoparticles themselves. This study seeks to contribute valuable insights into the diverse biological interactions of nanoparticles, informing risk assessments and the development of safer nanomaterials for various applications.