Cells cannot clear certain nanoparticles (NPs) according to recent research published by Adolphe Merkle Institute (AMI) researchers in the journal ACS Nano. These NPs are considered persistent, and their concentration levels are chiefly reduced through cell division.

Engineered NPs made of gold (Au NPs), silica (SiO₂ NPs), or super paramagnetic iron oxide (SPIONs) are already in use for various medical applications, including imaging, cancer irradiation therapy, as well as carriers for drug delivery. These NPs can be administered into the bloodstream by injection, ingestion, or inhalation, and transported to targeted sites. However, what happens to these NPs after reaching their target in cells and tissues is still somewhat unclear.

While some of these NPs are cleared by the body’s digestive and filtration systems, what happens to others ingested by macrophages, the white blood cells that hoover up anything reaching their surface, is not well known. Once absorbed, the NPs are transported in vesicles to lysosomes, a digestive organelle.  The AMI study investigated what happens to model NPs made of SiO₂ and Au after reaching the lysosomal organelle. The results showed that none of the particles used by the researchers were released by the macrophages.

Previous research had suggested that cell division (mitosis) could help reducing the load of accumulated NPs. The AMI study shows now that distribution of NPs after mitosis is however not shared equally. This could also have a knock-on effect in biomedical applications.

“The impact of this phenomenon on NPs used by nanomedical applications such as cancer research and therapy needs to be investigated further,” says AMI Professor Barbara Rothen-Rutishauser. “Because of the variations in NP load, these potentially significant differences must be considered when conducting experiments with dividing cells, such as for cancer cells.”

Reference: Bourquin, J.; Septiadi, D.; Vanhecke, D.; Balog, S.; Steinmetz, L.; Spuch-Calvar, M.; Taladriz-Blanco, P.; Petri-Fink, A.; Rothen-Rutishauser, B. Reduction of Nanoparticle Load in Cells by Mitosis but Not Exocytosis, ACS Nano, 2019, 13 (7), 7759