Wound-Healing Effects of Birch Bark and Propolis Extracts on Epidermolysis Bullosa Keratinocytes

Epidermolysis bullosa (EB) is a group of genetic diseases characterized by skin fragility. Although therapeutic options aim to accelerate wound-healing, improvement is needed; therefore, birch bark and propolis were investigated due to their beneficial biological properties. A representative ethanolic extract was analyzed by reversed-phase high-performance liquid chromatography with diode array detection (RP-HPLC-DAD) for chemical profiling of the raw materials. A hydrophobic natural deep eutectic solvent (HNaDES) for birch bark extraction, as well as a hydrogel and a bigel enriched with propolis and birch bark extract, were prepared and characterized by Fourier transform infrared (FT-IR) spectroscopy. Cytotoxicity and wound-healing potential were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and scratch assays in six human keratinocyte cell lines: two from healthy individuals, two from recessive dystrophic ΕΒ patients (RDEB), and two from laminin-332-deficient junctional EB patients (JEB). RP-HPLC-DAD revealed the presence of phenolic compounds (e.g., chrysin, pinocembrin, pinobanksin) and pentacyclic triterpenes (e.g., betulin and betulinic acid), characteristic of propolis and birch bark, respectively. FT-IR confirmed HNaDES formation and indicated physical interactions within the gels. All systems exhibited no cytotoxicity at 1 μg/mL and increased cell vitality. Moreover, in keratinocytes derived from JEB patients, hydrogel improved wound- healing significantly at 24 h, whereas bigel showed significant improvement at 8 h. The developed systems could be promising topical treatments.