Zeolite Encapsulation Decreases TiO 2 ‐photosensitized ROS Generation in Cultured Human Skin Fibroblasts †

ABSTRACT Sunscreens protect skin against sunburn. However, studies have demonstrated that UV‐irradiated sunscreen components such as titanium dioxide (TiO 2 ) promote the photogeneration of reactive oxygen species (ROS). Because encapsulation of TiO 2 within zeolites alters its photocatalytic activity, supra‐molecular composites based on NaY zeolite hosts containing TiO 2 guests were prepared, and the effects on ROS formation in cells under UVA‐irradiation evaluated. DCFH‐DA (2′,7′‐dichlorofluorescein diacetate) was used as a profluorescent probe to monitor intracellular ROS. The detection of in‐tracellular 2′,7′‐dichlorofluorescein (DCF) fluorescence by confocal microscopy revealed that DCFH‐DA was taken up, hydrolyzed and oxidized by yeast cells and cultured human skin fibroblasts within 20 and 6 min, respectively. Higher DCF fluorescence was observed in fibroblasts following UVA irra‐diation in the absence but not in the presence of the radical nitroxide, TEMPOL (4‐hydroxy‐2,2,6,6‐tetramethylpipery‐dine‐1‐oxyl), which exhibits superoxide dismutase‐mimetic and catalase‐mimetic activity. UVA‐induced fluorescence increased by ‐50% in the presence of 32‐nm anatase TiO 2 particles and decreased by essentially an equal amount in the presence of TiO 2 encapsulated within NaY zeolites (TiO 2 @NaY). Addition of the uncomplexed NaY host also decreased (by ∼30%) the amount of UVA‐induced fluorescence but, un‐expectedly, the combination of the free guest and host (TiO 2 @NaY) caused a doubling of the fluorescence. Protection of cells against TiO 2 ‐induced intracellular ROS by encapsulation suggests that supramolecular species may be beneficial in photoprotection of the skin. In contrast, the potentiation of TiO 2 ‐induced ROS by uncomplexed NaY points to a critical role for formulation when free TiO 2 is used as a sun screen ingredient.