Development and characterization of a new cosmetic formulation enriched with optimized Thanaka bark extract (H. crenulata)

Thanaka is a Burmese plant typical of traditional medicine, used for topical application. Coumarins give this plant beneficial properties for the skin, like antioxidant and anti-inflammatory capacities, as well as anti-acne and anti-age activities. This work aimed to develop a novel cosmetic formulation containing Thanaka extract by evaluating and comparing the chemical and biological properties of extracts obtained through Soxhlet (SE) and ultrasound-assisted extraction (UAE) using different solvents, in order to select the most effective extract for cosmetic applications. All the extracts were assessed regarding antioxidant capacity using spectrophotometric assays and total phenol content by Folin-Ciocalteu's assay. The extract samples named as 4UAE, 2UAE, 2SE, and 4SE with a higher antioxidant capacity, were then assessed for anti-collagenase activity and quantification of marmesin using High-Performance Liquid Chromatography coupled with Diode Array Detection (HPLC-DAD). With a value of 480.77 μg/g Dry Weight (DW), extract 2SE was found to have the highest marmesin content among the samples tested. The two extracts (2SE and 4UAE) with the highest antioxidant capacity were then in vitro tested on Human Gingival Fibroblasts (HGFs) for a biological evaluation of cell viability (MTT Assay), morphological analysis, gene expression of Matrix Metalloproteinase 9 (MMP9) and Collagen 1 (Col1), antioxidant capacity, and Prostaglandin E2 (PGE2) secretion. The in vitro results positively characterize Thanaka extracts, confirming their anti-collagenase activity and demonstrating their capability to stimulate Col1 synthesis, thus promoting extracellular matrix (ECM) deposition. A sample extracted using the SE method with ethanol at 70° was used to formulate a face cosmetic cream that was then further characterized in terms of density, pH, physicochemical, and microbial stability. The formulation's efficacy and safety were evaluated on 20 healthy volunteers after 30 days of daily use of the cosmetic cream. The local compatibility test, Trans Epidermal Water Loss (TEWL), deep and surface hydration, and skin elasticity were assessed. After the daily use of the face cream enriched with Thanaka extract, a decrease in the evaporation rate value was observed. After 30 days, image skin analyses with Antera 3D were also acquired to evaluate wrinkles and fine lines, redness (hemoglobin), color (melanin), and pores. Skin analysis demonstrated that the regular use of cosmetic face cream substantially improved overall skin health, showing a decreasing trend for the evaluated parameter from time 0 (t0) to day 30(t2). The inclusion of the selected promising extract in a topical cosmetic formulation confirmed an unquestionable anti-age activity, providing a valid basis for further research and dermatological uses of Thanaka bark.