Plant Foods for Human Nutrition (Dordrecht, Netherlands) · 6 authors, 4 centres
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This first report on Onosma riedliana reveals that its methanolic extract is rich in phenolic compounds (97.62 mg GAE/g) and exhibits potent antioxidant activity, while the ethyl acetate extract shows strong inhibition of cholinesterases and tyrosinase. The findings suggest O. riedliana is a promising source of natural bioactive compounds for pharmaceutical applications, particularly in neurodegenerative and skin disorders.
**Background:** The Onosma genus, comprising about 150 species, has a long history of traditional use for treating bronchitis, abdominal pain, fever, and skin burns. These plants are known to accumulate high levels of phenolic compounds, which are major carriers of therapeutic properties. Onosma riedliana, initially described by Binzet and Orcan, remains relatively unexplored. This study is the first to investigate the phenolic profiles, antioxidant properties, and enzyme inhibitory activities of three extracts (ethyl acetate, methanol, water) derived from O. riedliana.
**Methods:** The plant material was extracted using three solvents of varying polarity. Total phenolic and flavonoid contents were determined spectrophotometrically. Detailed phenolic composition was analyzed using LC-MS/MS. Antioxidant activity was assessed via six assays: phosphomolybdenum, CUPRAC, FRAP, DPPH, ABTS, and ferrous ion chelating. Enzyme inhibitory activities were evaluated against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), tyrosinase, α-amylase, and α-glucosidase. Relative antioxidant capacity indices (RACI) were calculated. Pearson correlation matrices were used to relate phenolic compounds to biological activities.
**Key Results:** The methanolic extract had the highest total phenolic content (97.62 ± 0.20 mg GAE/g) and flavonoid content (54.98 ± 0.05 mg RE/g). LC-MS/MS identified pinoresinol as the predominant compound in both ethyl acetate (2992.0 ± 38.9 μg/g) and methanolic (73628.2 ± 1256.9 μg/g) extracts. Hesperidin was the main flavonoid in the methanolic extract (32455.3 ± 27.7 μg/g). The methanolic extract showed the strongest antioxidant activity across all six assays, with IC50 values of 0.55 mg/mL (phosphomolybdenum), 0.27 mg/mL (CUPRAC), 0.20 mg/mL (FRAP), 0.30 mg/mL (DPPH), 0.34 mg/mL (ABTS), and 0.95 mg/mL (ferrous ion chelating). Its RACI value was 1.23, higher than other Onosma species. For enzyme inhibition, the ethyl acetate extract had the lowest IC50 values for AChE (1.43 mg/mL), BChE (5.39 mg/mL), α-amylase (1.75 mg/mL), and α-glucosidase (2.38 mg/mL). The methanolic extract showed the best tyrosinase inhibition (IC50 1.84 mg/mL, 57.16 mg KA/g). Correlation analyses indicated that flavonoids (luteolin, hesperidin, quercetin, kaempferol, apigenin) were primarily responsible for antioxidant and cholinesterase/tyrosinase inhibitory activities.
**Clinical Implications:** The high antioxidant capacity and enzyme inhibitory activities of O. riedliana extracts suggest potential applications in managing oxidative stress-related degenerative diseases (cardiovascular, inflammatory, cataracts, cancer) and neurodegenerative conditions (via cholinesterase inhibition). The tyrosinase inhibitory activity indicates possible use in skin disorder treatments. The methanolic extract's efficacy against α-amylase and α-glucosidase points to potential antidiabetic applications. These findings support the traditional use of Onosma species and highlight O. riedliana as a valuable source of natural bioactive compounds for pharmaceutical development.