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

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Abstract

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.

Section snippets

Materials and methods

Materials. Three nano titanium dioxide (TiO2) powders in the forms of anatase, rutile (Zhejiang Hongsheng Material Technology Co., Ltd.) and Degussa P25 (P25, anatase/rutile, Degussa company, Germany), were commercially available and used without further treatment (Table 1). Bovine serum albumin (BSA) and rabbit polyclonal antibody against 3-nitrotyrosine were purchased from Sigma. All solvents and other reagents were the highest purity commercially available. High voltage mercury lamp (a

TiO2/NO2--photocatalytic protein tyrosine nitration

As shown in Fig. 1A and B, protein tyrosine nitration was generated in the UV-irradiated reaction mixture containing 0.5 mg/ml BSA, 1.67 mg/ml TiO2 and 1 mM NO2-, which was detected by spectrophotometer (Fig. 1A) and Western blotting (Fig. 1B), respectively. There was no 3-nitrotyrosine formation from the treatment with TiO2 or NO2- alone, which demonstrated that TiO2 and NO2- were both essential for the photo-nitration. The production of 3-nitrotyrosine increased with prolonging the irradiation

Acknowledgments

This research was supported by the National Basic Research Program (973 Program) of China (No. 2006CB705606), the National Natural Science Foundation of China (No. 30670481), the Program for New Century Excellent Talents in University (No. NCET-05-0649), and E-Institutes of Shanghai Municipal Education Commission (No. E-04010).

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These authors contributed equally to this work.

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