Oxyresveratrol from mulberry (Morus alba L.) ameliorates post-inflammatory hyperpigmentation in vitro by anti-melanogenesis, inhibiting melanosome transfer, and providing photoprotection

• OXY has the ability to support the amelioration of post-inflammatory hyperpigmentation mechanisms. • OXY was purified from mulberry extract, a traditional Chinese medicine. • OXY effectively inhibited melanin synthesis in human melanocytes. • OXY significantly inhibited melanosome transfer to keratinocytes. • OXY can repair the barrier function and provide photoprotective properties in a UVB-induced keratinocyte damage model. Mulberry ( Morus alba L.) twigs are a traditional Chinese medicine and edible agricultural by-product. Oxyresveratrol (OXY) is one of the natural resorcinol-type polyphenols obtained from mulberry twigs with anti-melanogenesis effects. This study aimed to investigate the ameliorative effects and mechanisms of OXY on post-inflammatory hyperpigmentation (PIH) in vitro . The results of DPPH radical scavenging and tyrosinase inhibition assays showed that OXY exhibited potent antioxidant and tyrosinase inhibitory activities. In human melanocytes, OXY significantly down-regulated protein expression related to melanin synthesis and transport. A molecular docking study suggested that OXY could inhibit these GTPases (RAB27A, RAC1, and CDC42) activities in melanosome transfer processes. Furthermore, OXY significantly reduced inflammatory factor secretion, promoted human β-defensin production, and up-regulated the expression of barrier proteins in UVB-induced human keratinocytes. This research indicated that the OXY from mulberry twigs has potential applications in ameliorating PIH through its antioxidant, anti-melanogenic, melanosome transport inhibition, anti-inflammatory, and photoprotective properties.