Exploring the therapeutic potential and phenolic composition of two Turkish ethnomedicinal plants – Ajuga orientalis L. and Arnebia densiflora (Nordm.) Ledeb

Abstract

Ajuga orientalis L. and Arnebia densiflora (Nordm.) Ledeb. are plants traditionally used in Turkish ethnomedicine to manage common ailments. Nonetheless, there is currently a dearth of investigations geared towards highlighting the inhibitory properties of A. orientalis and A. densiflora against key carbohydrate hydrolyzing enzymes (α-amylase and α-glucosidase), tyrosinase, and cholinesterases (acetylcholinesterase and butyrylcholinesterase) involved in diabetes, post inflammatory hyperpigmentation, and neurodegenerative diseases, respectively. We aimed to shed light on the antioxidant potential and various enzymatic inhibitory properties of tested methanolic extracts of these plants. In vitro antioxidant activity, DNA protective effects, antimicrobial activity (against 8 bacteria, 10 fungal strains and 1 yeast), as well as phenolic compounds determination and HPLC (high performance liquid chromatography) analysis were performed. 17 phenolic components were quantified in tested extracts. Major phenolic compounds present in A. orientalis extract were chlorogenic acid, benzoic acid, and luteolin. A. densiflora extract revealed the presence of gallic acid, rutin, rosmarinic acid, quercetin, luteolin, and apigenin. A. densiflora showed a stronger antioxidant capacity, higher total phenolic (33.72 mg GAE/g), and total flavonoid contents (55.93 mgRE/g), as well as protection of DNA against hydroxyl radical compared to A. orientalis extract. The tested extracts showed similar antimicrobial activity with low effect against the bacterial and fungal strains. The tested extracts showed a slightly higher potential to inhibit tyrosinase activity, while inhibition of the activity of the other examined enzymes by the extracts was weak. The observed biological activities and presence of bioactive phytochemicals can open new perspectives to develop novel dietetic supplements.