INTRODUCTION: Photo‐activated titanium dioxide (TiO2) has been shown to catalyze the production of reactive oxygen species (ROS) acting against bacteria. Our group reported that exposure to infrared radiation (IR) was able to activate nanofibrillar TiO2 and induce cell death of Escherichia coli. However, elevated oxidative stress might trigger inflammation causing damage in surrounding tissue. It is important to investigate the inflammatory responses, since we proposed the therapeutic application of IR‐activated TiO2 in protection from infection.
METHODS: 1. Inflammatory responses were detected by measuring proinflammatory gene expression. Briefly, human cell line A375 was treated with TiO2 nanofibers exposed by IR‐laser up to 30s. Cells were harvested at 3 and 6 hours, mRNA was isolated, and IL‐8 gene expression as an indicator of inflammatory response was measured by real‐time PCR. 2. To detect if oxidative stress was upregulated after IR/TiO2 treatment, 2',7'‐dichlorofluorescein diacetate (DCFH‐DA)‐DCF method was utilized. DCFH‐DA can be transferred to fluorescent DCF, which is proportional to the level of hydrogen peroxide in cells. 3. Cell death was visualized by microscopy, and live cells were stained using crystal violet.
RESULTS: IL‐8 expression level was not induced by IR/TiO2 treatment at both 3 and 6 hour‐time point. Hydrogen oxidative content in cell culture was undetectable. In addition, we did not observe cell death after 24 hours of treatment.
DISCUSSION: Our data suggested that IR/TiO2 treatment did not induced acute inflammatory responses, oxidative stress, and cell death indicating that the amount of ROS generated by this photocatalytic process was not toxic to human cells but sufficient to perform antibacterial effect. In addition, ROS might degrade more rapidly because of the presence of antioxidant enzymes inside the cells. Further investigation using human blood cells and primary mouse cells is in progress.