In Vitro and In Silico Antioxidant Activity of Lemon-scented Gum (Eucalyptus citriodora Hook.) Cultivated in North Sumatra

Eucalyptus citriodora Hook, also known as lemon-scented gum is a perennial plant that has been cultivated in North Sumatra for its essential oils and is being developed as a source medicinal compounds due to its bioactivities. While this plant has been extensively utilized for practical purposes in North Sumatra, empirical evidence regarding its antioxidant activity remains undisclosed, thereby piquing the interest of natural product chemists. To investigate the potential antioxidant activity of crude bioactive extracts from E. citriodora leaves, both in vitro and in silico studies were conducted. Crude extract was obtained by maceration of simplicia in methanol, followed by solvent-solvent extraction using hexane, and ethyl acetate. Antioxidant activity was determined using DPPH radical scavenging activity (in vitro). An in silico study was done using four protein targets namely; lipoxygenase, cytochrome P450 family 2 subfamily C member 9 (CYP2C9), NADPH-oxidase, and xanthine oxidase with curcumin and gallic acid as standard compounds. The highest yield was obtained from the hexane extract (54.3 g), followed by the methanol (42.5 g) and ethyl acetate extracts (11.6 g). The ethyl acetate extract of E. citriodora leaves showed the highest antioxidant activity (IC50 = 44.78 µg/mL), followed by the methanol (IC50 = 65.13 µg/mL), and hexane extracts (IC50 = 140.45 µg/mL). The best docking score expressed as high binding free energy was obtained on xanthine oxidase (∆G = -6.7 kcal/mol) which was higher than the standard compound, gallic acid (∆G = -6.5 kcal/mol). The high content of methyl gallate in the leaves of E. citriodora implies its prospect to be formulated into herbal drugs for the treatment hyperuricemia in the future.