Volatile Natural Deep Eutectic Solvents (VNADESs) for Extraction of Shikonin Derivatives from Echium vulgare Roots and Evaluation of Biological Activity

Background: Shikonins are natural naphthoquinones that exhibit a range of biological activities. They are typically extracted using nonpolar solvents; however, green extraction approaches remain underexplored. Methods: Phytochemical profiling of E. vulgare root extracts was performed using HPLC-ESI-QTOF-MS/MS and quantitative analysis using HPLC-PDA. Shikonin extraction was performed using VNADESs based on thymol, camphor, menthol and benzyl alcohol. The feasibility of removing the VNADES from the extracts via freeze-drying was assessed. The cytotoxic, antioxidant, anti-inflammatory and antimicrobial activities of the hexane extract and the selected VNADES-based extract (TBa 2:8) were compared. Results: Eight shikonin derivatives were identified in the extracts. VNADES extracts contained comparable amounts of shikonin to hexane extracts; however, freeze-drying resulted in significant shikonin content loss. TBa 2:8 extract exhibited noticeably lower cytotoxicity than the hexane extract while its antioxidant potential depended on the assay applied. In contrast to the hexane extract, TBa 2:8 demonstrated the ability to reduce intracellular ROS and NO levels. However, the hexane extract exhibited stronger antimicrobial activity. Conclusions: VNADES systems enable efficient extraction of shikonin derivatives with performance comparable to hexane. Although the resulting extracts exhibit multidirectional biological activity, it remains challenging to remove the VNADESs effectively without losing the shikonins.