Abstract: Xu Yuting, Wang Peiru, Han Jiatong, Wang Xiuli Shanghai Skin Disease Clinical College of Anhui Medical University, Shanghai 200443, China （Xu YT）; Institute of Photomedicine, Tongji University School of Medicine, Shanghai Skin Disease Hospital, Shanghai 200443, China （Wang PR, Han JT, Wang XL） Corresponding author: Wang Xiuli, Email: wangxiuli20150315@163.com 【Abstract】 Objective To evaluate the protective effect of dietary n-3 polyunsaturated fatty acids （PUFA） on ultraviolet-induced acute skin photodamage in SKH-1 hairless mice, and to explore its mechanism. Methods Totally, 50 SKH-1 hairless mice were equally divided into 5 groups to be fed with forages with the ratios of n-3 PUFA to fatty acid being 0, 12.5%, 25%, 50% and 100% respectively （control group, 12.5%, 25%, 50% and 100% n-3 PUFA groups）. On day 8 after feeding, the back of mice in the 5 groups were irradiated by a solar ultraviolet simulator at 2 minimum erythema doses （MED） to establish an acute photodamage model. After 24 hours, cutaneous reactions on the back of mice were observed by naked eyes and dermoscopy, and skin biopsy specimens were subjected to hematoxylin and eosin （HE） staining for observing the epidermal structure, intercellular edema, inflammatory cell infiltration and photodamaged cells. Immunohistochemical staining was performed to determine the of inflammatory cytokines including interleukin-1 beta （IL-1β）, IL-6 and tumor necrosis factor alpha （TNF-α）, and enzyme-linked immunosorbent assay（ELISA） to measure the protein of the above 3 inflammatory cytokines in the tissue homogenate. Results Compared with the control group and 12.5% n-3 PUFA group, the 25%, 50% and 100% n-3 PUFA groups all showed a milder degree of acute skin photodamage, epidermis thickening, intercellular edema, and inflammatory cell infiltration. The number of photodamaged cells per high-power field （× 100） was significantly higher in the control group and 12.5% n-3 PUFA group （17.50 ± 4.93, 14.25 ± 1.71, respectively） than in the 25%, 50% and 100% n-3 PUFA groups （6.50 ± 1.73, 4.75 ± 2.06, 4.50 ± 1.73, respectively; F = 19.1, P < 0.001）. Immunohistochemical results showed that IL-1β, IL-6 and TNF-α were expressed to different extents in the epidermis and dermis among the 5 groups at 24 hours after ultraviolet radiation. Compared with the control group and 12.5% n-3 PUFA group, the 25%, 50% and 100% n-3 PUFA groups showed significantly lower of the above 3 inflammatory cytokines （P < 0.001）. ELISA revealed that the levels of IL-1β, IL-6 and TNF-α in the skin tissues of the mice were significantly lower in the 25%, 50% and 100% n-3 PUFA groups than in the control group and 12.5% n-3 PUFA group （P < 0.05）. Conclusions When the ratio of n-3 PUFA to fatty acid reaches more than 25%, dietary n-3 PUFA has protective effects against ultraviolet-induced acute photodamage,. Moreover, the higher the content of n-3 PUFA is, the stronger the protective effect is. It is suggested that n-3 PUFA may inhibit the inflammatory reaction through the arachidonic acid pathway.

Key words: n-3polyunsaturated fatty acids, ultraviolet, acute ultraviolet injury