A comparative study of the essential oil extracts of Centaurea alexanderina different parts: GC-MS analysis, antimicrobial, antioxidant, and anti-hyperglycemic activities.

Abstract

Background: Natural products have been a cornerstone in the field of drug discovery for centuries, they have provided numerous therapeutic agents that have significantly impacted modern medicine. Centaurea alexanderina is a canescent herb that is native to Egypt and Libya and reported in Egyptian folk medicine as an anti-hyperglycemic, antioxidant, and antimicrobial herb. It is an understudied species, thusly, the target of this contribution was to perform a comparative study of the influence of plant part variation on its chemical and pharmacological characteristics. In this context, essential oil extracts from different parts of C. alexanderina (flowers, stems, leaves, and roots) have been analyzed chemically and tested for their antioxidant, antimicrobial, and anti-hyperglycemic activities.

Methods: The essential oil extracts from different parts of C. alexanderina have been prepared and their chemical compositions have been analyzed using GC-MS technique. Antimicrobial activities of different essential oil extracts were evaluated via the agar cup diffusion method. DPPH radical scavenging and FRAP assays were used for determination of the antioxidant capacity. Anti-hyperglycemic activities of the four essential oil extracts under study were investigated via α-glucosidase inhibition assay. A computational study has been performed using molecular docking of the identified compounds in the most active essential oil extracts (leaves and roots) against α-glucosidase enzyme using PDB entry 5NN8.

Results: A GC-MS analysis of the four essential oil extracts revealed high levels of non-terpenoid hydrocarbons in three essential oil extracts (flower, stems, and leaves) and alcohols in roots essential oil extract, followed by fatty acids in flowers, diterpenoids in stems, steroids in leaves, and fatty acid esters in roots. Roots and stems essential oil extracts exhibited selective activity against Pseudomonas aeruginosa (P. aeruginosa), whereas leaves essential oil extract showed activity against both Salmonella enterica (S. enterica) and Escherichia coli (E. coli). Essential oil extracts of different parts of the plant exhibited DPPH free radical scavenging activity with IC₅₀ values of 128, 134, 152, and 163 μM for flowers, roots, stems, and leaves essential oil extracts; respectively, while in FRAP assay, the results showed different pattern; flowers revealed the highest activity followed by leaves, roots, and stems (107.50 ± 3.64, 125.80 ± 4.2, 139.4 ± 5.27, and 155.59 ± 5.27 ug/mL, respectively). In vitro evaluation of anti-hyperglycemic activity via inhibition of α-glucosidase enzyme assay unveiled leaves and roots essential oil extracts as the most inhibitors with IC₅₀ values of 349 and 369 μg/mL; respectively. The molecular docking study of detected metabolites in the most active essential oil extracts against human α-glucosidase enzyme (PDB: 5NN8) revealed moderate to high binding affinities (-4.6 to -7.3 kcal/mol for leaves and -4.4 to -7.9 kcal/mol for roots essential oil metabolites).

Conclusion: Current research demonstrated the variations in chemical composition and biological activities of essential oil extracts from different parts of Centaurea alexanderina and reported anti-hyperglycemic, antioxidant, and antimicrobial potentials of the different essential oil extracts.