Abstract
Calycosin, a bioactive isoflavonoid isolated from root extracts of Astragalus membranaceus, has been reported to inhibit melanogenesis, the mechanism of which remains undefined. In this study, we interrogated the mechanistic basis by which calycosin inhibits melanin production in two model systems, i.e., B16F10 melanoma cells and zebrafish embryos. Calycosin was effective in protecting B16F10 cells from α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis and tyrosinase activity. This anti-melanogenic effect was accompanied by decreased expression levels of microphthalmia-associated transcription factor (MITF), a key protein controlling melanin synthesis, and its target genes tyrosinase and tyrosinase-related protein-2 (TRP-2) in calycosin-treated cells. Mechanistically, we obtained the first evidence that calycosin-mediated MITF downregulation was attributable to its ability to block signaling pathways mediated by cAMP response element-binding protein (CREB) and p38 MAP kinase. The protein kinase A (PKA) inhibitor H-89 and p38 inhibitor SB203580 validated the premise that calycosin inhibits melanin synthesis and tyrosinase activity by regulating the PKA/CREB and p38 MAPK signaling pathways. Moreover, the in vivo anti-melanogenic efficacy of calycosin was manifested by its ability to suppress body pigmentation and tyrosinase activity in zebrafish embryos. Together, these data suggested the translational potential of calycosin to be developed as skin-lightening cosmeceuticals.
Highlights
The past decade has witnessed a growing interest in identifying natural anti-melanogenic or skin-lightening agents from medicinal herbs based on safety considerations [1,2]
To interrogate the role of individual melanogenic mediators by which calycosin inhibited melanin synthesis, we examined the effects of calycosin versus Arbutin on the protein expression of five key mediators, including Melanocortin 1 receptor (MC1R), microphthalmiaassociated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2), in α-melanocyte-stimulating hormone (α-MSH)-treated B16F10 cells
To explore the underlying mechanisms by which calycosin inhibited MITF expression and downstream melanogenesis-related factors, we investigated whether calycosin affected protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP) response elementbinding protein (CREB), p38 Mitogen-activated protein kinases (MAPK), and Jun N-terminal kinase (JNK) signaling pathways in α-MSH-treated B16F10 cells by Western blot analysis
Summary
The past decade has witnessed a growing interest in identifying natural anti-melanogenic or skin-lightening agents from medicinal herbs based on safety considerations [1,2]. These efforts have led to the characterization of a series of natural products, including carotenoids and polyphenols, concerning their abilities to suppress melanogenesis by blocking melanin production [2,3,4]. Tyrosinase, the essential and rate-limiting enzyme in melanogenesis, catalyzes the hydroxylation of L-tyrosine to 3,4-dihydroxyphenylalanine (DOPA) and the oxidation of DOPA to DOPAquinone [9], which acts as the substrate for the synthesis of eumelanin. DOPAquinone reacts with cysteine to form cysteinyl DOPAs, which are further oxidized and polymerized to produce yellow-to-red soluble pheomelanin [10]
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