Abstract:

Liu Yale*, Ge Qin, Li Zhangjun, Geng Songmei, Xiao Shengxiang, Yao Cuiping, Zhang Zhenxi, Zeng Weihui. *Department of Dermatology, Second Affiliated Hospital of Xi′an Jiaotong University, Xi′an 710004, China Corresponding author: Zeng Weihui, Email: zengwh88@163.com 【Abstract】 Objective To investigate the protective effect of gold nanoparticles against skin photoaging through photothermal effects in female ICR mice, and to explore its possible mechanisms. Methods A total of 32 healthy female ICR mice were randomly and equally divided into four groups: normal control group receiving no treatment, model group receiving ultraviolet radiation alone, red laser group irradiated with red laser followed by ultraviolet radiation, gold nanoparticle group pretreated with gold nanoparticle solution under occlusion with a black plastic film for 30 minutes followed by red laser and ultraviolet radiation. Ultraviolet radiation was conducted thrice a week for 14 weeks, and the hairs in an area sized about 16 cm2 on the back of mice were shaved before each radiation in the model group, red laser group and gold nanoparticle group. At the end of experiment, the skin appearance of mice was observed by naked eyes and dermoscopy. Then, all the mice were sacrificed and skin samples were resected from the tested areas on the back. Haematoxylin-eosin （HE） and Masson′s staining was performed to observe the changes of skin structure and collagen fibers, and the image analysis software ImageJ was used to calculate the area fraction （AA%） occupied by collagen fibers. The DCFH-DA probe was utilized to determine the level of reactive oxygen species （ROS）, and enzyme-linked immunosorbent assay （ELISA） was performed to measure the expression of matrix metalloproteinase-13 （MMP-13） in skin samples. Statistical analysis was carried out by one-way analysis of variance （ANOVA） for intergroup comparisons followed by the least significant difference （LSD）-t test for multiple pair-wise comparisons. The simple linear regression analysis was performed to assess the relationship between ROS levels and MMP-13 expression. Results After ultraviolet radiation, a series of characteristic photoaging changes were observed in the skin of mice in the model group, such as squamation, brown-yellowish discoloration, coarsening, thickening, appearance of deep wrinkles and lack of flexibility. Dermoscopy also showed skin coarseness, crusting and brown spots with breakage of and hemorrhage from capillaries in the model group. Compared with the normal control group, the model group showed significant increases in epidermal thickness （81.32 ± 7.09 vs. 38.42 ± 13.64 μm, P < 0.05）, dermal thickness （352.75 ± 40.08 vs. 188.50 ± 27.83 μm, P < 0.05）, ROS levels （5 124 152.80 ± 754 119.22 vs. 3 502 085.29 ± 135 089.06 fluorescence intensity of DCF per milligram of protein, P < 0.05） and MMP-13 expression （3 895.42 ± 136.06 vs. 2 414.73 ± 105.96 g/L, P < 0.05）, but a significant decrease in the area fraction occupied by collagen fibers （31.94% ± 8.56% vs. 48.63% ± 11.32%, P < 0.05） with an elevation in abnormal elastic materials. Both skin appearance and histological changes improved obviously in the gold nanoparticle group compared with the model group. The skin was significantly thinner in the gold nanoparticle group （epidermal thickness: 48.70 ± 13.35 μm; dermal thickness: 253.74 ± 36.28 μm, P < 0.05） than in the model group. Moreover, the gold nanoparticle group showed a significant elevation in the area fraction occupied by collagen fibers （41.54% ± 12.10%, P < 0.05）, but a significant reduction in ROS levels （3 516 963.35 ± 67 436.36 fluorescence intensity of DCF per milligram of protein, P < 0.05） and MMP-13 expression levels （2558.25 ± 102.72 g/L, P < 0.05） compared with the model group. There were no significant differences between the gold nanoparticle group and normal control group in epidermal thickness, ROS levels or MMP-13 expression （all P > 0.05）. The simple linear regression analysis showed that ROS levels were positively correlated with MMP-13 expression （r = 0.864, P = 0.018）. Conclusion The photothermal effects of gold nanoparticles can protect ICR mice from skin photoaging to a certain degree, likely by down-regulating the generation of ROS and expression of the downstream factor MMP-13.