Abstract
The abnormal regulation of melanin synthesis leads to a wide range of pigmentary disorders. Although various melanin biosynthesis inhibitors have been developed, their efficacy and long-term safety needs to be further improved, and thus the goal of this study is to develop promising natural compound inhibitors of melanin biosynthesis. Here, we obtained aglycone flavonoid extract through the microwave-assisted hydrolysis of glycoside extract from Korean mistletoe in acidic condition. The aglycone extract inhibited tyrosinase activity more efficiently with better antioxidant activity than glycoside extract in vitro. The microwave-assisted aglycone extract of mistletoe was further analyzed for in vivo activity, and the results showed the aglycone extract inhibited both early melanocyte development and melanin synthesis more efficiently in zebrafish embryo in a dose-dependent manner. Our in vivo toxicity assay quantitatively measured cell death in zebrafish embryos and showed that the microwave-assisted aglycone extract of mistletoe had no significant effect on cell death (p < 0.001), indicating that aglycone extract is more biocompatible than glycoside extract. Furthermore, our in vitro and in vivo analyses successfully identified and characterized velutin, an aglycone of a homoflavoyadorinin B glycoside, as a major inhibitory component in the microwave-assisted mistletoe extract. Ultimately, this study showed that the novel natural compound inhibitor velutin, which was generated through microwave-assisted extraction from mistletoe, improved the efficacy of melanin biosynthesis inhibition with little toxicity.
Highlights
Melanin is a natural pigment that is synthesized in melanocytes through a multistep process, and it is involved in the determination of skin and hair color [1,2]
We identified velutin as a major natural compound inhibitor from the extract and further characterized its effect on melanin biosynthesis inhibition
In order to assess the potential improvement of natural compound inhibitors in Korean mistletoe, crude ethanol extract of mistletoe was first prepared and further processed through microwave-assisted hydrolysis
Summary
Melanin is a natural pigment that is synthesized in melanocytes through a multistep process, and it is involved in the determination of skin and hair color [1,2]. Melanin synthesis is regulated by multistep catalytic reactions of enzymes such as tyrosinase, tyrosine hydroxylase isoform I, phenylalanine hydroxylase, tyrosinase-related protein 1, and tyrosinase-related protein. Tyrosinase is a copper-containing enzyme that plays a key role in the rate-limiting step of melanin synthesis by the hydroxylation of L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). Tyrosinase is a target enzyme for the development of functional cosmetic agents and therapeutics against pigmentary disorders. Certain molecules obtained through chemical synthesis and natural resources, such as hydroquinone, azelaic acid, arbutin, and kojic acid, have been reported to prevent skin pigmentation by inhibiting tyrosinase activity [4,6]. Due to the cytotoxicity, low efficacy, and low stability of the existing substances, there is still a need for natural substances with improved efficacy and safety
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