Onosma aucheriana, O. frutescens, and O. sericea: Phytochemical profiling and biological activity

It is known that Onosma species are frequently used in the treatment of various ailments such as bronchitis, strangury, leucoderma, abdominal pain and fever. The aim of this study was to investigate the antioxidant, tyrosinase and alpha-amylase inhibitory activities of the MeOH extracts obtained from the aerial parts of Onosma aucheriana DC., O. frutescens Lam., and O. sericea Willd. Total phenolic/flavonoid and liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analyzes were also performed to determine the chemical composition of the extracts. In antioxidant activity tests, except for ferrous ion chelating, the activity of O. frutescens was found to be significantly higher than the others. The antioxidant activity of this species in 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), cupric reducing antioxidant capacity (CUPRAC), ferric reducing antioxidant power (FRAP), and phosphomolybdenum tests were found to be 1.14, 1.04, 0.53, 0.35 and 1.18 mg/mL, respectively. The ferrous ion chelating assays resulted in the superiority of O. aucheriana [the half maximal inhibitory concentration (IC50): 2.57 mg/ mL] . In tyrosinase and alpha-amylase inhibitory activity tests, it was found that the activity potentials of O. aucheriana and O. sericea extracts were quite close to each other. Tyrosinase and a-amylase inhibitory activity of O. aucheriana were determined as 2.19 and 2.51 mg/mL. Additionally, the IC50, values of O. sericea on the same enzymes were measured as 2.28 and 2.50 mg/mL. As a result of the spectrophotometric analysis, when compared with the others, it was understood that O. frutescens and O. sericea extracts were richer in phenolics and flavonoids, respectively. Chromatographic analyzes have shown that the extracts contain high amounts of rosmarinic acid, apigenin 7-glucoside, luteolin 7-glucoside, hesperidin, hyperoside, ferulic acid, vanillic acid, caffeic acid and 4-hydroxybenzoic acid.