Determination of antioxidant, antimicrobial, anticholinesterase, antityrosinase, antidiabetic and antiglaucoma activities of essential oils from three different Thymus species and their chemical characterization by GC-MS analysis

Abstract

The present study aims to perform a comprehensive chemical characterization of the essential oils of Thymus pubescens var. pubescens (TPEO), Thymus leucotrichus var. leucotrichus (TLEO), and the endemic Thymus canoviridis (TCEO) using GC-MS, besides evaluating the potential antidiabetic, anticholinesterase, antimicrobial, antioxidant, antiglocouma, and antityrosinase activities of these essential oils. The antioxidant activity was assessed using various bioassays including DPPH, ABTS, DMPD, FRAP, CUPRAC, and Fe3+ reducing assays. The IC50 values of TPEO, TLEO, and TCEO for α-glycosidase were 28.32, 28.79, and 57.57 μg/mL, respectively. For tyrosinase, the IC50 values were 359.9, 270.87, and 597.43 μg/mL, respectively. The IC50 values for acetylcholinesterase were calculated as 44.15, 36.75, and 34.99 μg/mL, respectively, while for carbonic anhydrase, the IC50 values were 21.70, 24.75, and 24.45 μg/mL, respectively. The quantitiy of total phenolics present in TPEO, TLEO, and TCEO were determined to be 10.50, 34.50, and 32.50 μg GAE/mg essential oil, respectively. The TPEO, TLEO, and TCEO exhibited distinct antioxidant activities on DPPH, ABTS, and DMPD. TPEO showed antimicrobial activity against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Acinetobacter baumannii bacterias. TLEO exhibited effective antimicrobial activity against S. aureus; The last of these TCEO demonstrated notable antimicrobial activity towards S. aureus, Enterococcus faecalis, E. coli, K. pneumoniae, Pseudomonas aeruginosa, P. mirabilis, A. baumannii. Additionaly, GC-MS revealed that the major components are TPEO (pulegone 29.01%, piperitenone 17.17%), TLEO (germacrene D 9.59%), and TCEO (carvacrol 52.87%). The essential oils possessed a range of biological activities, including antioxidant, antidiabetic, anticholinesterase, antityrosinase, antiglocouma and antimicrobial activities.