Shape and surface properties of titanate nanomaterials influence differential cellular uptake behavior and biological responses in THP-1 cells

We investigated cellular uptake behavior and biological responses of spherical and fibrous titanate nanomaterials in human monocyte THP-1 cells. Two titanate nanofibers (TiNFs), namely TF-1 and TF-2, were synthesized from anatase TiO2 nanoparticles (TNPs) via hydrothermal treatment. The synthesized TiNFs and TNPs were thoroughly characterized for their size, crystallinity, surface area and surface pH. TF-1 (∼2 µm in length) was amorphous with an acidic surface, while TF-2 (∼7 µm in length) was brookite with a basic surface. The results demonstrated that none of these titanate nanomaterials resulted in significant cytotoxicity, even at the highest doses tested (50 µg/ml), consistent with an absence of ROS generation and lack of change of mitochondrial membrane potential. While no cytotoxic effect was found in the titanate nanomaterials, TF-2 tended to decrease the proliferation of THP-1 cells. Furthermore, TF-2 resulted in an inflammatory cytokine response, as evidenced by dramatic induction of IL-8 and TNF-α release in TF2 but not TF-1 nor TNPs. These results suggest that shape of titanate nanomaterials plays an important role in cellular internalization, while surface pH may play a prominent role in inflammatory response in THP-1 cells.