Increased Level of α2,6-Sialylated Glycans on HaCaT Cells Induced by Titanium Dioxide Nanoparticles under UV Radiation

As one of the most widely used nanomaterials, the safety of nano-TiO2 for human beings has raised concern in recent years. Sialylation is an important glycosylation modification that plays a critical role in signal transduction, apoptosis, and tumor metastasis. The aim of this work was to investigate the cytotoxicity and phototoxicity of nano-TiO2 with different crystalline phases for human skin keratinocytes (HaCaT cells) under ultraviolet (UV) irradiation and detect sialic acid alterations. The results showed that the mixture of crystalline P25 had the highest cytotoxicity and phototoxicity, followed by pure anatase A25, whereas pure rutile R25 had the lowest cytotoxicity and phototoxicity. A25 and R25 had no effects on the expression of sialic acids on HaCaT cells. However, HaCaT cells treated with P25 and UV showed an increased level of alterations in alpha 2,6-linked sialic acids, which was related to the level of reactive oxygen species (ROS) generated by nano-TiO2 and UV. The abundance of alpha 2,6-linked sialic acids increased as ROS production increased, and vice versa. Antioxidant vitamin C (VC) reversed the abnormal expression of alpha 2,6-linked sialic acids caused by nano-TiO2 and protected cells by eliminating ROS. These findings indicate that nano-TiO2 can alter the sialylation status of HaCaT cells under UV irradiation in a process mediated by ROS.