754 Near-infrared light 790-1000 nm causes photoaging in vivo and in vitro

      Objective: Near-infrared radiation (NIR), which is a composition of sunlight with a 700-2000 nm wavelength, is associated with skin aging such as wrinkles and slacks. On the other hand, NIR irradiation is effective for the improvement of skin photo damage. In the present study, we examined the effect of NIR on the skin in vivo and in vitro using a NIR irradiation apparatus that controls wave length and irradiation dose. Methods: The NIR irradiation apparatus has a halogen flash lamp where the light is white similar to sunlight (790-1700 nm). The skin of hamsters or mice was irradiated every other day for 1.75-7 min with NIR (190 mW/cm2). After fixing skin tissues at 1, 3, and 5 days post-irradiation, hematoxylin-eosin and immunohistochemical staining and the measurement of intracutaneous temperature were performed. The expression of reactive oxygen species (ROS) and inflammatory cytokines was analyzed in NIR-irradiated human epidermal keratinocytes (HEK). Results: NIR irradiation with 780-1700 nm caused epidermal thickness, sebaceous hyperplasia, and the augmentation of matrix metalloproteinase 1 (MMP-1) expression in the auricle skin of the hamsters. In addition, the intracutaneous temperature was increased up to 47 oC. Furthermore, the increase of ROS and TNF-α production was detectable in the NIR-irradiated HEK. However, neither said histological alteration nor the increase of MMP-1, intracutaneous temperature, ROS, and TNF-α was detectable in a filter-selected NIR (>1000 nm) irradiated skin and HEK. Conclusion: These results provide novel evidence that NIR with 790-1000 nm wavelength causes photoaging actions such as epidermal thickness, sebaceous hyperplasia, and the augmentation of MMP and TNF-α production in epidermis in vivo, which are closely associated with an increase in intracutaneous temperature and ROS levels.