From soil to cosmetic industry: Validation of a new cosmetic ingredient extracted from chestnut shells

Sustainability arises as a challenge in the last decades and the cosmetic field is not an exception. The search for new cosmetic active principles extracted from food byproducts through eco-innovative technologies has emerged as a novel concept. However, the European Regulation is very restrictive and different assays should be performed to guarantee the products' efficacy and safety. Considering a multidisciplinary approach, this paper aims to compare chestnut shells extracts prepared by three different green techniques - Subcritical Water Extraction (SWE), Ultrasound-Assisted Extraction (UAE) and Supercritical Fluids Extraction (SFE) - regarding antimicrobial activity, hyaluronidase and elastase inhibitory activities, in-vitro cytotoxicity on dermal cells (HaCaT and HFF-1) and skin permeation (using Franz cells coupled to human skin). The best extract was tested on skin and ocular 3D models and through an in-vivo patch test to evaluate its irritancy and safety. The results demonstrated the antimicrobial properties of the extracts (particularly against Staphylococcus aureus) as well as the capacity to inhibit the hyaluronidase (IC50 = 0.76-54.36 mg/mL) and elastase (33.56-82.70% at 0.4 mg/mL) activities. Regarding in-vitro cell assays, UAE and SWE extracts revealed the best outcomes. Between 0.1 and 100 mu g/mL, none of the extracts conducted to a decrease of cell viability in both cell lines (HaCaT and HFF-1). The ex-vivo assay proved that SWE extract led to a higher polyphenol's permeation (1061.6 mu g/g dw), being selected for further assays. Ellagic acid was the major polyphenol that permeated the human skin (732.1-847.0 mu g/g dw). The 3D skin and ocular models evidenced absence of irritation by SWE extract, without decreasing cell viability and releasing IL-1 alpha. Finally, an in-vivo patch test confirmed the absence of irritation in humans based on the acute irritation index of 0.50 achieved 24 h after the patch removal. To the best of our knowledge, this is the first study that validated by in-vitro and in-vivo assays, and in accordance with the European Regulation 1223/2009, a new cosmetic ingredient extracted from chestnut shells.