Cytotoxicity of benzophenone-3, an organic ultraviolet filter, caused by increased intracellular Zn2+ levels in rat thymocytes.

Benzophenone-3 (BP-3) is often used as an ultraviolet (UV) light filter in sunscreen products. Although BP-3 protects the human skin and hair from damage caused by excessive UV radiation, it is reported to exhibit toxic effects in human. However, the cytotoxicity of BP-3 on various cells is still not well understood. In the present study, the cytotoxicity of BP-3 against rat thymocytes was evaluated using a flow cytometric technique with fluorescent probes. Cell mortality increased significantly after 3 h of exposure to 300 µM BP-3, whereas the mean intensity of 5-chloromethylfluorescein diacetate (5-CMF) fluorescence and cellular content of non-protein thiols decreased significantly. However, the membrane potential of thymocytes was not change by BP-3 treatment. Moreover, intracellular Zn2+ levels increased significantly in a concentration-dependent manner in response to 30 µM BP-3 or higher. The BP-3-induced changes in intracellular Zn2+ levels and non-protein thiol content increased the vulnerability of thymocytes to oxidative stress. We concluded that BP-3-induced cytotoxicity may be caused by oxidative stress associated with an increase in intracellular Zn2+ levels.