Protective Effects of Titanium Dioxide-based Emulsion after Short-term and Long-term Infrared-A Ray Irradiation on Skin Cells

To accurately evaluate the protective effects of titanium dioxide-based emulsion from infrared-A rays (IRA) irradiation in daily life, we assessed the harmful effects of natural level of IRA irradiation on human skin cells. Using a well-defined solar IRA simulator, short-term (less than seven days) IRA irradiation on fibroblasts at 34°C elicited an increase in the matrix metalloproteinase-1 (MMP1) mRNA level and decrease in the collagen type-1 α-1 (COL1A1) mRNA level. While short-term IRA exposure showed negligible effects on cell proliferation at 34°C, long-term (24 days) IRA irradiation significantly decreased the proliferation of fibroblasts at the same temperature. However, in the presence of heat stress at 43°C, short-term IRA exposure also elicited severe damage including reduction in cell proliferation and procollagen type 1 C-terminal peptide (PIP) level. In addition, formulated titanium dioxide-based emulsion (IRA protective cream; IRC) with an infrared-A protection factor value of ten could successfully protect cells from damage by short-term and long-term IRA exposures. In this study, we demonstrated that IRC reduces mild and severe damages elicited by natural level of IRA irradiation mimicking system after short-term and long-term exposures.