Tsai_2024_Antioxidants.(Basel)_14_

Rhamnus formosana is a creeping evergreen shrub endemic to Taiwan. In traditional medicine, Rhamnaceae plants are used as herbal remedies for conditions such as itching, difficulty urinating, and constipation. This study explores the inhibitory effects of various solvent extracts and bioactive components of R. formosana on alpha-glucosidase, tyrosinase, acetylcholinesterase (AChE), and antioxidant activity. The 100 degreesC water extract exhibited strong antioxidant activity in DPPH, ABTS, superoxide, and FRAP assays. The methanol extract demonstrated the highest alpha-glucosidase inhibitory effect, while the ethanol extract displayed potent AChE inhibition and the acetone extract showed the most potential tyrosinase inhibitory activity among the extracts. Five main biocomponents were isolated and evaluated for their bioactivities. Among them, kaempferol (1) and quercetin (2) exhibited notable antioxidant activity in DPPH and ABTS assays. Particularly, kaempferol (1) performed the best alpha-glucosidase inhibitory effect, physcion (5) showed the strongest AChE inhibition, and quercetin (2) demonstrated the most potential for tyrosinase inhibitory activity. Further molecular docking studies revealed that there may be stronger binding mechanisms between bioactive components and target enzymes (including alpha-glucosidase, acetylcholinesterase, and tyrosinase) than the positive control. These findings suggest that bioactive extracts and compounds from the stems of R. formosana may have potential as natural antioxidant, anti-alpha-glucosidase, anti-AChE, and anti-tyrosinase drug candidates or dietary supplements for the management of oxidative stress-related conditions, including hyperglycemia, pigmentation disorders, and neurodegenerative diseases.