Onosma demirizii: Chemical composition, antioxidant and enzyme inhibitory activity

Abstract

The primary objectives of the present work were to determine the chemical composition, antioxidant potential and enzyme inhibitory activity of three extracts derived from Onosma demirizii (Boraginaceae), including methanol, water and ethyl acetate, and to chemically characterize the phytochemicals underlying this activity. A rapid, reproducible, simple, and sensitive method, which had been previously validated, was employed to identify 31 phenolics based on liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The conducted analysis of LC-ESI-MS/MS indicated that the methanol extract of O. demirizii was the richest in terms of both flavonoids and phenolics (42.75 mg GAEs/g extract and 59.90 mg QEs/g extract, respectively). The compounds with greatest abundance in methanol extract were hesperidin (177957 mg/g extract), chlorogenic acid (31815 mg/g extract), hyperoside (10199 mg/g extract), rosmarinic acid (8857 mg/g extract) and pinoresinol (2502 mg/g extract). Moreover, methanol extract exhibited the greatest activity in all antioxidant assays except for ferrous ion-chelating assay. The EC50/IC50 values of the extract in CUPRAC and FRAP reducing power, phosphomolybdenum, DPPH and ABTS radical scavenging assays were determined to be 0.85, 1.47, 0.47, 1.78, and 1.67 mg/mL, respectively. However, the ferrous ion-chelating assay was superior for water extract (1.07 mg/mL). Contrary to the results obtained from the assays of antioxidant activity, ethyl acetate extract was observed to be effective in enzymatic inhibition tests. The extract exhibited the highest activity against AChE and BChE (IC50 values 1.04 and 1.47 mg/mL, respectively). These extracts and compounds can be useful for the management of human diseases that are linked to oxidative stress.