WU Yuxuan, LIU Changshu, LIU Jianguo, LI Kexin, LIU Dasong, ZHOU Peng
Overexposure to UV irradiation could increase reactive oxygen species that exceeds the defense capacity of endogenous antioxidant enzyme systems, and accumulate peroxidation products, resulting in an imbalance of the body's redox homeostasis. Further activation of related signaling pathways triggers collagen degradation and skin inflammation, ultimately leading to skin photoaging. It is manifested as a series of skin damage such as redness, dryness, lack of elasticity, and deepening of wrinkles. With the continuous improvement of aesthetic standards, the need to prevent and delay skin aging caused by UV irradiation is increasing. At present, improving antioxidant capacity is an important way to protect skin from UV irradiation-induced oxidative damage. Pomegranate extract is rich in polyphenols such as punicalagin and ellagic acid. Haematococcus pluvialis is one of the best raw materials for the production of astaxanthin. Acerola cherry can provide a variety of vitamins, especially vitamin C. As a fat-soluble antioxidant, vitamin E is often used with the water-soluble vitamin C. The above four substances are potential raw materials for antiphotoaging due to their antioxidant properties. The results of cell and biochemistry experiments in vitro often cannot be correlated to the antioxidant effect in vivo. The results from different experiments in vivo could not be compared directly to determine the difference in antioxidant effect and mechanism of different antioxidants on skin. Effects of pomegranate extract, H. pluvialis, acerola cherry extract and acerola cherry extract+vitamin E on skin antioxidant activity in mice was studied. Sixty male BALB/c nude mice were randomly divided into six groups: control, model, and four antioxidant groups, and an UVA+UVB irradiation-induced skin photoaging model was established. The model treatment lasted for two weeks, three times a week, and each time the UV irradiation dose was 5 600 mJ/cm2. The UVA and UVB irradiation intensity was 1.44 mW /cm2 and 0.14 mW/cm2, respectively. During the modeling period, the four antioxidant groups were given daily gavage of 292 mg/kg bw pomegranate extract, 103 mg/kg bw H. pluvialis, 556 mg/kg bw acerola cherry extract and 556 mg/kg bw acerola cherry extract+2.66 mg/kg bw vitamin E. The control and model groups were given an equal volume of normal saline. Oxidative stress indicators, including reactive oxygen species, malondialdehyde, protein carbonyl, antioxidant enzymes including superoxide dismutase, glutathione peroxidase and catalase, collagen degradation metabolism indicators including metalloproteinase-1, 9 and 12, and inflammatory indexes including IL-6 and TNF-α, were determined by the kit. The mRNA relative expression levels of nuclear factor erythroid 2 related factor 2/antioxidant response element (Nrf2/ARE) redox pathway related factors, such as Nrf2, heme oxygenase-1 (HO-1) and nicotinamide adenine dinucleotide phosphatequinone oxidoreductase1, were determined by reverse transcription-PCR (RT-PCR) method. The value of a*, moisture content and elasticity were also measured. The resulting data were used to comprehensively analyze the effects of different antioxidants on skin antioxidation and antiphotoaging. The results showed that compared with the control group, the model group treatment significantly increased the contents of reactive oxygen species, protein carbonyl, IL-6 and TNF-α, up-regulated the expression of matrix metalloproteinase-1, 9 and 12, increased the a* value of skin, and significantly down-regulated the expression of glutathione peroxidase, catalase, and nicotinamide adenine dinucleotide phosphatequinone oxidoreductase1. It suggested that UV irradiation could disrupt the redox balance, stimulate the degradation of extracellular matrices such as collagen and elastin, trigger skin inflammation, and affect skin phenotype. Different antioxidants or their combination had an improvement effect on skin, and the effect of H. pluvialis and acerola cherry+vitamin E was better. First, compared with the model group, H. pluvialis and acerola cherry+vitamin E significantly reduced the contents of reactive oxygen species and protein carbonyl, and up-regulated the expression of glutathione peroxidase, indicating that the redox homeostasis could be maintained by promoting the expression of antioxidant enzymes and alleviating the degree of oxidative stress, thereby protecting the skin from oxidative damage caused by UV irradiation. Second, H. pluvialis and acerola cherry+vitamin E significantly down-regulated the expression of matrix metalloproteinase-1 and 12, thus maintaining the collagen and elastin stability, the skin′s tensile and elastic structure, and the integrity of tissue morphology. Furthermore, H. pluvialis and acerola cherry+vitamin E significantly reduced the contents of IL-6 and the a* value of skin, suggesting that it could alleviate skin inflammation, reduce skin redness, and have an improvement effect on skin appearance. In conclusion, H. pluvialis and acerola cherry+vitamin E inhibit the expression of matrix metalloproteinases and the secretion of inflammatory factors by maintaining the redox balance, i.e., regulating the relationship between antioxidant defense, collagen metabolism and inflammation to recover skin damage caused by UV irradiation and delay photoaging. It is expected to provide a reference for the selection of raw materials and for the development of products with skin improvement effects. This research mainly compared the skin antioxidant effect of a single natural antioxidant or the combination of antioxidants. In the follow-up research, it is suggested to combine with other skin active ingredients such as peptides to check if there is any synergy effect on skin heath. In addition, the products of each antioxidant after digestion and absorption in the body and its skin care mechanism can be further studied.
