Bioactive Properties and Chemical Compositions of Essential Oils From Three Nepeta L. Species, Two Endemic, Grown in Türkiye

Nepeta is one of the largest genera in the Lamiaceae family. The aim of this study is to evaluate (DPPH• and ABTS+ scavenging tests), antidiabetic (α-amylase and α-glucosidase enzymes inhibition), and anticholinesterase (acetylcholinesterase and butyrylcholinesterase enzymes inhibition) activities of methanolic, aqueous extracts and essential oils obtained from flowering aerial parts of N. cilicia Boiss. ex Benth., N. isaurica Boiss. & Heldr. ex Benth., and N. sulfuriflora P.H.Davis. Furthermore, essential oils extracted from these plants were analysed for their chemical composition by GC–MS/MS. Also, anatomy and morphology of these plants were evaluated. Total phenolic and tannin contents were analysed. The major compounds identified in the essential oils of Nepeta species were as follows: caryophyllene oxide (24.8%) and phytol (17.7%) in N. cilicia, α-cadinol (13.6%) and ledol (8.0%) in N. isaurica, and 1,8-cineole (70.4%) in N. sulfuriflora. The plants are perennial, and they have unicellular to multicellular non-glandular and multicellular glandular trichomes. In antidiabetic assays, N. cilicia methanolic extract showed the highest α-amylase inhibition (31.66%), while N. isaurica essential oil had the strongest α-glucosidase inhibition (14.25%). For anticholinesterase activity, N. sulfuriflora essential oil was most effective against acetylcholinesterase (8.63%), and N. isaurica MeOH extract had the highest butyrylcholinesterase inhibition (13.24%). It was determined that especially methanolic extracts had higher % inhibition value on ·+ABTS and DPPH•. When a comparison was made in terms of total phenol and total tannin content, it was observed that N. sulfuriflora species was one step ahead. In conclusion, the study revealed that the three Nepeta species—N. cilicia, N. isaurica, and N. sulfuriflora—possess significant bioactive properties, particularly in their antioxidant, antidiabetic, and anticholinesterase activities.