(+)-Usnic Acid as a Promising Candidate for a Safe and Stable Topical Photoprotective Agent

• Published in: Molecules (Basel, Switzerland) Switzerland), 2021-08, Vol.26 (17), p.5224
• Main Authors: Galanty, Agnieszka, Popiół, Justyna, Paczkowska-Walendowska, Magdalena, Studzińska-Sroka, Elżbieta, Paśko, Paweł, Cielecka-Piontek, Judyta, Pękala, Elżbieta, Podolak, Irma
• Format: Article
• Language: English
• Subjects: Acids; Acrylates - chemistry; Benzofurans - chemistry; Benzofurans - pharmacology; Cosmetics; Enantiomers; Fibroblasts - drug effects; Fibroblasts - radiation effects; Handedness; Humans; Keratinocytes; Keratinocytes - drug effects; Keratinocytes - radiation effects; Lichens; Melanocytes; Melanocytes - drug effects; Melanocytes - radiation effects; normal skin cells; Octocrylene; Permeability; photoprotection; Radiation-Protective Agents - chemistry; Radiation-Protective Agents - pharmacology; Skin; Skin - drug effects; Sunscreen; Ultraviolet filters; Ultraviolet radiation; Ultraviolet Rays; Usnic acid
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules26175224

The study aimed to examine whether usnic acid-a lichen compound with UV-absorbing properties-can be considered as a prospective photoprotective agent in cosmetic products. Moreover, a comparison of two usnic acid enantiomers was performed to preselect the more effective compound. To meet this aim, an in vitro model was created, comprising the determination of skin-penetrating properties via skin-PAMPA assay, safety assessment to normal human skin cells (keratinocytes, melanocytes, fibroblasts), and examination of photostability and photoprotective properties. Both enantiomers revealed comparable good skin-penetrating properties. Left-handed usnic acid was slightly more toxic to keratinocytes (IC 80.82 and 40.12 µg/mL, after 48 and 72 h, respectively) than its right-handed counterpart. The latter enantiomer, in a cosmetic formulation, was characterized by good photoprotective properties and photostability, comparable to the UV filter octocrylene. Perhaps most interestingly, (+)-usnic acid combined with octocrylene in one formulation revealed enhanced photoprotection and photostability. Thus, the strategy can be considered for the potential use of (+)-usnic acid as a UV filter in cosmetic products. Moreover, the proposed model may be useful for the evaluation of candidates for UV filters.