Abstract
When exposed to ultraviolet radiation, the human skin produces profuse reactive oxygen species (ROS), which in turn activate a variety of biological responses. Mounting ROS levels activate tyrosinase by mobilizing α-melanocyte-stimulating hormone in the epidermis and finally stimulates the melanocytes to produce melanin. Meanwhile, the Keap1-Nrf2/ARE pathway, which removes ROS, is activated at increased ROS levels, and antioxidant compounds facilitates the dissociation of Nrf2. In this study, we explored the possible suppressing effects of antioxidant compounds and tyrosine inhibitors on melanin formation and the promotory effects of these compounds on ROS scavenging. The antioxidant activity of glabridin (GLA), resveratrol (RES), oxyresveratrol (OXYR), and phenylethylresorcinol (PR) were investigated via the stable free radical 2,2-diphenyl-1-picrylhydrazyl method. The inhibitory effects of the four compounds and their mixtures on tyrosinase were evaluated. l-Tyrosine or 3-(3,4-dihydroxyphenyl)-l-alanine (l-DOPA) was used as a substrate. The results showed that all mixtures did not exhibit synergistic effects with the l-tyrosine as a substrate, suggesting that l-tyrosine is not suitable as a substrate. However, the mixtures of “GLA:RES,” “GLA:OXYR,” “OXYR:RES,” and “PR:RES” demonstrated synergistic effects (CI < 0.9, p < 0.05), whereas “GLA:RES” and “PR:OXYR” indicated an additive effect (0.9 ditive1, p < 0.05). Furthermore, we used a molecular docking strategy to study the interactions of the four compounds with tyrosinase and l-DOPA. The molecular docking result is consistent with that of the experiment. Finally, we selected RES + OXYR and used PIG1 cells to verify whether OXYR synergistically promotes RES activity on tyrosinase. The two agents had a synergistic inhibitory effect on tyrosinase activity. These results provided a novel synergistic strategy for antioxidants and tyrosinase inhibitors, and this strategy is useful in skin injury treatment.
Highlights
The human skin is constantly exposed to ultraviolet radiation (UVR), which is an induction factor of reactive oxygen species (ROS)
Our results indicated that the capability of the compounds for free radical scavenging are ranked as follows: OXYR > PR > RES > GLA
Pigmentation is a local color darkening shown on the skin surface, such as melasma and senile plaques. It is caused by UVA ray exposure, which leads to inflammatory reactions, changing the microenvironment of melanocytes in the skin
Summary
The human skin is constantly exposed to ultraviolet radiation (UVR), which is an induction factor of reactive oxygen species (ROS). Nrf regulates several phase II detoxification and antioxidant genes involved in cellular defenses against oxidative stress [4,5]. Skin pigmentation is another mechanism for the prevention of damage due to UVR. Tyrosinase (EC 1.14.18.1) is a copper-containing enzyme, widely distributed in fungi, plants, and animals [8]. It catalyzes the pigmentation of skin and is directly related with pigmentation disorders in mammals [9,10]. It is a key target for the discovery and screening of novel inhibitors because of its central role in melanogenesis
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