Safety and Efficacy of Dextran-Rosmarinic Acid Conjugates as Innovative Polymeric Antioxidants in Skin Whitening: What Is the Evidence?

Background: Melanins are high molecular weight pigments responsible for the mammalianskin and hair colour and play a key role in skin protection from UV radiation; however, theiroverproduction and excessive accumulation lead to pigmentation problems including melasma,freckles, uneven colouring, and age spots. Therefore, the modulation of melanin synthesis representsa critical issue in medicine and cosmetology. In the present study, an innovative polymeric antioxidantto be used as skin whitening agent is developed by the conjugation of dextran with rosmarinic acid.

Methods: Dextran-rosmarinic acid conjugates (DEX-RA) were synthesized in a one-pot methodstarting from Origanum vulgare aqueous leaf extract and dextran. The total polyphenol content andthe antioxidant activity were assessed by Folin-Ciocalteau assay and 2,2-diphenyl-1-picrylhydrazylradical (DPPH) and bleaching tests, respectively. The efficacy of DEX-RA was evaluated by inhibitionof tyrosinase activity, in vitro diffusion and stability studies and in vivo studies. The biocompatibilityof the conjugates was investigated by 3-[4,5-Dimethylthiaoly]-2,5-diphenyltetrazoliumbromide(MTT) and EPISKIN™ model.

Results: Efficacy and safety studies confirmed the antioxidant andtyrosinase inhibitory activities and the biocompatibility of the synthesized conjugates.

Conclusion:The polymeric conjugates, comparing to the free antioxidant, show a long-lasting efficacy combinedto an enhanced stability resulting in an improved performance of the cosmetic formulations preparedusing this innovative whitening agent as a bioactive ingredient.