Exploring the Pharmacological Potential of Onosma riedliana: Phenolic Compounds and Their Biological Activities.

Onosma riedliana Binzet & Orcan, a traditionally used plant species, has been explored for its therapeutic potential in this study. The work presented here is the first report on the phenolic profile and biological activity of this species. Three extracts of varying polarity were prepared, with the methanolic extract containing the highest phenolic content (97.62 ± 0.20 mgGAE/g). Key phenolic compounds identified included pinoresinol, hesperidin, 4-hydroxybenzoic acid, and p-coumaric acid. The methanolic extract exhibited exceptional antioxidant properties, rivaling Trolox as a positive control, primarily attributed to hesperidin and luteolin. Moreover, the ethyl acetate extract demonstrated remarkable inhibition of cholinesterase and tyrosinase enzymes, while the methanolic extract displayed potent activity against carbohydrate hydrolytic enzymes, α-amylase and α-glucosidase. Again, phenolic compounds were shown to be responsible for the inhibition of cholinesterases and tyrosinase, but not for α-amylase and α-glucosidase. These findings underscore Onosma riedliana's potential for incorporation into diverse pharmaceutical formulations, given its multifaceted bioactivity.

Phytochemical Composition, Antioxidant, and Enzyme Inhibition Activities of Methanolic Extracts of Two Endemic Onosma Species.

Onosma species have been used as a dye for hundreds of years due to their dark red pigments. These species have also been used by mankind in the treatment of various diseases since ancient times. This work analyzed the phytochemical composition in methanol extract of two endemic Onosma species (O. lycaonica and O. papillosa). Methanolic extract of these species varied in the content of flavonoids and phenolics. The flavonoids were found higher in O. papillosa [32.9 ± 0.3 mg QEs (quercetin equivalent)/g extracts] while the phenolics were higher in O. lycaonica [43.5 ± 1.5 mg GAEs (gallic acid equivalent)/g extracts]. ESI-MS/MS (electrospray ionization-mass spectrometry) revealed the presence of 25 compounds in O. lycaonica and 24 compounds in O. papillosa. The former was richer than the latter for apigenin, luteolin, eriodictyol, pinoresinol, apigenin 7-glucoside, rosmarinic acid, luteolin 7-glucoside, ferulic acid, vanillin, caffeic acid, 4-hydroxybenzoic acid, (+)-catechin3,4-dihydroxyphenylacetic acid. The O. papillosa exhibited low EC50 (1.90 ± 0.07 mg/mL) which indicated its strong phosphomolybdenum scavenging activity as compared to O. lycaonica. However, the O. lycaonica showed low IC50 or EC50 for 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+), cupric reducing antioxidant power (CUPRAC), ferric reducing antioxidant power (FRAP) and ferrous ion chelating activity, as compared to O. papillosa. The results proved the presence of potent antioxidant compounds in O. lycaonica. Further, the plant extracts significantly varied for enzyme inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), but the plant extracts did not significantly differ for inhibition of α-glucosidase, α-amylase, and tyrosinase. Onosma species deserve further research towards developing novel drugs to treat oxidative diseases.