Identities and Spatial Distribution of Active Antioxidative Components in Ligustrum lucidum Ait. Leaves

Despite that the leaves of Ligustrum lucidum Ait. (LLA) have been used in traditional Chinese medicine for more than 2000 years, their medicinal potential remains underexplored compared with the fruits of this plant species. Therefore, the aims of this study were to investigate the antioxidative activities of different solvent fractions of LLA leaf extract and to identify the active components and their spatial distribution within the leaf tissue. Among all solvent fractions tested, the ethyl acetate and n-butanol fractions showed the strongest antioxidative activities in the 1,1-diphenyl-2-picrylhydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid, and fluorescence recovery after photobleaching assays. In total, 19 and 21 compounds were identified in the ethyl acetate and n-butanol fractions, respectively, with flavonoids, iridoids, and triterpenes being predominant. Analysis using desorption electrospray ionization-post-photoionization-mass spectrometry imaging identified 20 compounds that were mainly distributed in the leaf epidermis and mesophyll. These findings provide a comprehensive reference resource that will aid our understanding of the medicinal value of LLA leaves and lay the scientific foundation for their further development and use as a source of natural antioxidants.