Investigation of Enzyme Inhibitory Activities, Antioxidant Activities, and Chemical Properties of Leaves Using LC-QTOF-MS and RP-HPLC.

Since the leaves of some species are used in traditional folk medicine for diabetes, this study investigated the in vitro antidiabetic effect (α-glucosidase and α-amylase) of leaves. Additionally, the current study investigated the antihypercholesterolemic (cholesterol esterase), antiobesity (pancreatic lipase), and antioxidant activities (i.e., total antioxidant capacity, DPPH (2,2-Diphenyl-1-picrylhydrazyl) radical scavenging activity, metal chelating activity, and ferric-reducing antioxidant power) of leaves. The aqueous-alcoholic leaf extract inhibited α-amylase, α-glucosidase, and pancreatic lipase with the half-maximal inhibitory concentration values of 7.74 ± 0.72, 11.08 ± 3.96, and 168.43 ± 26.10 µg/mL, respectively. It was determined that the crude extract had high DPPH radical scavenging activity, ferric-reducing power, and moderate metal chelating activity. The ethyl acetate (EtOAc) subextract obtained by the liquid-liquid fractionation of the crude extract showed potent α-amylase and α-glucosidase inhibitory activities. The EtOAc subextract (5.794 ± 0.027 g/100 g subextract) was standardized by reversed-phase high-performance liquid chromatography based on β-pentagalloyl glucose, which showed inhibitory effects on both amylase and glucosidase enzymes. Fifteen compounds, seven of which are organic acid derivatives and eight of which are flavonoids, were identified by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) analysis in the crude extract of leaves. Seven of the fifteen phenolic compounds detected in the crude extract by LC-QTOF-MS have both glucosidase and amylase inhibitory effects. As a result, leaves can be a potential source for compounds with high antioxidant effects that show inhibitory effects on enzymes involved in carbohydrate digestion in the prevention and treatment of diabetes or can be evaluated as a standardized extract.