Unveiling the antioxidant potential of Curcuma amada Roxb. leaf essential oil : An in silico and in vitro investigation of major constituents

Elevated levels of human peroxiredoxin 5 (Prdx5), a cytoprotective antioxidant enzyme protects cellular compartments from oxidative damage induced by peroxides. In recent years, essential oils are regarded a viable source of non-toxic antioxidant substances with a higher safety profile. Curcuma species have been shown to inhibit lipid peroxidation levels and enhance antioxidant enzyme activities. Thus, the present study was designed to screen potential antioxidant agents from C. amada leaf essential oil (CALEO) to interact and support the Prdx5 enzyme activity using in vitro and computational approaches. The essential oil obtained from was chemically characterised using GC-MS. The analysis identified 36 constituents with camphor (17.51 %), spathulenol (12.00 %) and curdione (10.27 %) as the major constituents of CALEO. Moreover, the antioxidant effects of the oil were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS ) free radical scavenging assays, in which it demonstrated high DPPH (IC50 = 6.91 ± 0.04 μg/mL) and ABTS (IC50 = 5.86 ± 0.06 μg/mL) radical scavenging effects as compared to positive control. Subsequently, molecular docking analysis wascarried out between the key compounds of CALEO and Prdx5 protein. Amongst all, β caryophyllene, germacrone and ar -turmerone exhibited strong binding affinity (< -5.8 kcal/mol) against Prdx5 as compared to ascorbic acid (-5.3 kcal/mol). Furthermore, molecular dynamicsparameters such as RMSD (root mean square deviation), RMSF (root mean square fluctuation), Rg (radius of gyration), solvent accessible surface area (SASA), secondary structure and intermolecular H-bond plotted for the top scoring docked molecules indicated stability andminimal fluctuations over a 100 ns simulation period. Molecular mechanics poisson-boltzmann surface area (MM/PBSA) analysis revealed that Vander Waals interactions were the major contributor for stabilizing the complexes. Additionally, chemical absorption distributionmetabolism- excretion-toxicity (ADMET) analysis was conducted that revealed favourable pharmacokinetic and toxicity profiles for the lead compounds. Density functional theory (DFT) analysis was performed to investigate global reactivity parameters including MEP (molecular electrostatic potential), ELF (electron localization function), LOL (local orbital locator) and NCI-RDG (non-covalent interactions-reduced density gradient) for β-caryophyllene, germacrone, ar-turmerone and ascorbic acid. Ar-turmerone and germacrone displayed a small energy gap and higher reactivity compared to ascorbic acid. These findings suggest that germacrone and ar-turmerone may serve as promising novel antioxidant agents.