Nano titanium dioxide photocatalytic protein tyrosine nitration: A potential hazard of TiO2 on skin

Protein tyrosine nitration is a prevalent post-translational modification which occurs as a result of oxidative and nitrative stress, it may be directly involved in the onset and/or progression of diseases. Considering the existence of nano titanium dioxide (TiO2) in environment and sunscreen products along with the high content of nitrite in sweat, the UV-exposed skin may be a significant target for the photosensitized damage. In this paper, tyrosine nitration of bovine serum albumin (BSA) was initiated in the UV-irradiated reaction mixture containing 0.2–3.0 mg/ml of three commercially nano TiO2 products and 0.25–1.0 mM NO2-. It was found that anatase TiO2 and Degussa P25 TiO2 showed prominent photocatalytic activity on promoting the formation of protein tyrosine nitration, and the optimum condition for the reaction was around physiological pH. Meanwhile, the photocatalytic effect of rutile on protein tyrosine nitration was subtle. The potential physiological significance of nano TiO2-photocatalytic protein nitration was also demonstrated in mouse skin homogenate. Although the relationship between photocatalytic protein tyrosine nitration and chronic cutaneous diseases needs further study, the toxicity of nano TiO2 to the skin disease should be paid more attention in the production and utilization process.