Impact of titanium dioxide particle size on macrophage production of intracellular reactive oxygen species

Objectives: The aim of this study was to investigate the response of THP-1 monocyte-derived macrophages following exposure to titanium dioxide nanoparticles (TiO₂ NPs) and microparticles (TiO₂ MPs) in an in vitro system. Design: THP-1 monocytes were maintained in RPMI medium and transformed into M0 macrophages using Phorbol 12-myristate 13-acetate (PMA). TiO₂ particle size characterization was performed using scanning electron microscopy (SEM) and dynamic light scattering (DLS) technology. A viability study using an XTT assay was performed by treating THP-1-derived macrophages with TiO₂ NPs (<100 nm) and TiO₂ MPs (<5 μm) at concentrations ranging from 100, 50, 25, 12.5, 6.25 and 3.125 μg/mL. Macrophages were then treated with three different concentrations of NPs and MPs (5, 20 or 100 μg/mL) for 24 h, and ROS production and TiO₂ particle cellular uptake were measured using ROS assays and flow cytometry, respectively. Results: There was no significant change in the viability of THP-1 monocytes after treatment with TiO₂ NPs and MPs. The uptake of both particles was confirmed and showed an increase in ROS generation, and the MPs produced more ROS than NPs. The increase in ROS generation with NPs was concentration-dependent. Conclusion: Uptake of TiO₂ NPs and MPs in macrophages at subcytotoxic levels generate ROS in a size- and dose-dependent manner.