To investigate the effect of n-3 polyunsaturated fatty acid (n-3 PUFA) on preventing skin photoaging.

Eight-month-old C57B1/6 female mice were divided into two groups, n-3 PUFA group and control group. In the n-3 PUFA group, 100 μL of fish oil rich in n-3 PUFA eicosapentaenoic acid [18% eicosapentaenoic acid (EPA) and 12% decosahexaenoic acid (DHA)] was fed daily, and the backs of the mice were depilated after 1 month of feeding, and then the mice were subjected to ultraviolet B (70 mJ/cm²) irradiation treatment, minimum erythema dose, 3 times a week and each time for 20 s, for 1 month. The control group only irradiated and did not feed n-3 PUFA. At the end of the experiment, the back skin changes of the two groups of mice were observed, including grayscale of skin melanin deposition and the width of the skin; the expression of the melanocyte inducing transcription factor (MITF) mRNA was verified by reverse transcription-polymerase chain reaction. Tissues of the back skin of mice were fixed with paraffin, and then sectioned with sirius red. The thickness of skin tissue was calculated and the collagen content was measured. The expression of inflammatory macrophage related factors monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-α was measured by reverse transcription-polymerase chain reaction. And the expression of collagen Ⅰ, collagen Ⅲ, extracellular matrix metalloproteinase (MMP)-2, MMP-9. Data comparisons were performed using Student′s t-test.

The grayscale of skin melanin deposition of n-3 PUFA group was 0.87±0.39, which was significantly lower than that of the control group (2.25±0.45), the difference was statistically significant (t=2.28, P<0.05). The expression of MITF mRNA in the n-3 PUFA group was 0.89±0.02, which was also significantly lower than that in the control group (1.00±0.03), the difference was statistically significant (t=2.33, P<0.05). After examination, the skin texture of the control group was more confusing than the n-3 PUFA group; the width of the n-3 PUFA group was 9.65±0.68, and the width of the control group was 14.30±0.73, the difference between the two groups was statistically significant (t=4.65, P<0.05). Observed by sirius red staining, the skin thickness of the n-3 PUFA group was (218.40±20.40) μm, which was significantly higher than that of the control group [(131.60±15.99) μm], the difference was statistically significant (t=3.35, P<0.05). The collagen content of n-3 PUFA group [(13.90±0.99) mg/g] was higher than that of the control group [(10.45±0.44) mg/g], the difference was statistically significant (t=3.18, P<0.05); The expression of collagen Ⅰ in the n-3 PUFA group was 1.29±0.09, which was higher than that in the control group (0.98±0.09), the difference was statistically significant (t=2.19, P<0.05), but there was no statistically significant difference in the expression of collagen Ⅲ in the two groups (t=1.01, P=0.32). The expression of inflammatory macrophage-associated factors MCP-1 and TNF-α in the n-3 PUFA group were 0.74±0.06 and 0.67±0.06, which were lower than those of the control group 1.00±0.09, 1.00±0.06, the differences between the two groups were statistically significant (t=2.25, 3.51; with P values below 0.05); the expression levels of MMP-2 and MMP-9 in n-3 PUFA group were 0.58±0.04, 0.74±0.05, which were louer than those of the control group (1.00±0.06, 1.00±0.05), the differences were statistically significant between the two groups (t=5.09, 3.24, with P values below 0.05).

n-3 PUFA ameliorated photoaging through increasing collagen synthesis, decreasing macrophage infiltration and MMPs expression levels, it has potential clinical application value.