Inhibitory effects of n-hexane fraction from hydro-methanolic (2:3) extract on α-amylase and α-glucosidase activities of sepal of Salmalia malabarica: An approach through in vitro study

Alpha-Amylase and Alpha-Glucosidase Enzyme Inhibition and Antioxidant Potential of 3-Oxolupenal and Katononic Acid Isolated from Nuxia oppositifolia

Nuxia oppositifolia is traditionally used in diabetes treatment in many Arabian countries; however, scientific evidence is lacking. Hence, the present study explored the antidiabetic and antioxidant activities of the plant extracts and their purified compounds. The methanolic crude extract of N. oppositifolia was partitioned using a two-solvent system. The n-hexane fraction was purified by silica gel column chromatography to yield several compounds including katononic acid and 3-oxolupenal. Antidiabetic activities were assessed by α-amylase and α-glucosidase enzyme inhibition. Antioxidant capacities were examined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) scavenging assays. Further, the interaction between enzymes (α-amylase and α-glucosidase) and ligands (3-oxolupenal and katononic acid) was followed by fluorescence quenching and molecular docking studies. 3-oxolupenal and katononic acid showed IC₅₀ values of 46.2 μg/mL (101.6 µM) and 52.4 μg/mL (119.3 µM), respectively against the amylase inhibition. 3-oxolupenal (62.3 µg/mL or 141.9 μM) exhibited more potent inhibition against α-glucosidases compared to katononic acid (88.6 µg/mL or 194.8 μM). In terms of antioxidant activity, the relatively polar crude extract and n-butanol fraction showed the greatest DPPH and ABTS scavenging activity. However, the antioxidant activities of the purified compounds were in the low to moderate range. Molecular docking studies confirmed that 3-oxolupenal and katononic acid interacted strongly with the active site residues of both α-amylase and α-glucosidase. Fluorescence quenching results also suggest that 3-oxolupenal and katononic acid have a good affinity towards both α-amylase and α-glucosidase enzymes. This study provides preliminary data for the plant's use in the treatment of type 2 diabetes mellitus.

α-Glucosidase Inhibitory Activity of Phenolic Rich Extracts Obtained from the Seeds of Melastoma saigonense (Kuntze) Merr

The aim of this study was to perform a phytochemical analysis of Melastoma saigonense seed extracts and to determine their α-glucosidase inhibitory activity. The extracts from seeds of M. saigonense indicated that the total phenolic content was in the range between 233.46 and 967.22 mg GAE/g DE, whereas the flavonoids content was in the range between 359.96 and 850.84 mg QE/g DE. The present study of antidiabetic inhibitory activity by in vitro α-glucosidase revealed that the crude extracts using ethyl acetate (EA), butanol (BU) and final aqueous residue extracts (AQ) exhibited a strong α-glucosidase inhibitory effect (IC50 4.42-11.95 μg/mL). The ethyl acetate and butanol extracts of seeds of Melastoma saigonense (Kuntze) Merr. were further fractionated by silica gel column chromatography into four fractions (EAF1−EAF4) and five fractions (BUF1−BUF5), respectively and their bioactivities were investigated. The nine fractions exhibited significant α-glucosidase inhibitory activity (p < 0.05) with an IC50 between 3.42-34.77 μg/mL which is less than the IC50 for standard acarbose (IC50 = 507.26 μg/mL). Among all the fractions, BUF1 and EAF1 exhibited high inhibitory activity against α-glucosidase with BUF1 showing the highest inhibitory activity (IC50 = 3.42 μg/mL). The dominant phenolic acids were sinapic, gallic, ferrulic, syringic, gallic and caffeic acids and the prominent flavonoids were myricetin and quercetin. These findings suggest that the seeds of M. saigonense have potential as a source of antidiabetic agent (s).