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Background: Plant-phenolics and flavonoids, including gallic acid, quercetin and rutin, are considered as safe inhibitors for α-glucosidase. This study aimed to compare antioxidant and α-glucosidase inhibitory activities of gallic acid (GA), quercetin (QUE) and rutin (RUT).Materials and Methods: Pure compounds of GA, QUE, and RUT were used. Their antioxidant and inhibitory activity on α-glucosidase were investigated spectroscopically, including their kinetic analysis and interaction mechanism by docking simulation.Results: All the tested compounds (GA, QUE, and RUT) showed good antioxidant activity better than the standards ascorbic acid (AA) and butylated hydroxytoluene (BHT), with QUE showing the highest antioxidant activity based on 2,2-diphenyl1-picrylhydrazyl (DPPH) radical scavenging activity. Based on their reducing properties, the activities of the compounds follow the following order: AA > GA > BHT > QUE > RUT. Both GA and RUT induced a competitive type of inhibition, with activities stronger than acarbose (IC50 = 823 μg/mL), whereas QUE inhibited in a mixed type manner. The IC50 of GA, QUE, and RUT were 220.12, 65.52, and 224.55 μg/mL respectively. The results obtained from molecular docking indicate that all compounds have affinity in the active site pocket of α-glucosidase, with the hydrogen bond being the major force involved in each compound binding to the enzyme.Conclusion: In conclusion, QUE has better antioxidant and α-glucosidase inhibitory activity than GA and RUT. This work provides insights into the interactions between GA, QUE, and RUT and α-glucosidase.Keywords: docking, gallic acid, α-glucosidase, rutin, quercetin

Premna serratifolia, commonly known as Arogo in Tentena-Sulawesi, is a popular vegetable. As a promising herbal tea and food ingredient, further investigation is required to find the best knowledge for medicinal use of P. serratifolia leaves. This research investigated the antioxidant activity of the ethanol (EEPS) and water (WEPS) extracts of P. serratifolia leaves, based on their scavenging activities on DPPH radicals and their reducing capacities (CuPRAC, total antioxidant/phosphomolybdenum, and ferric thiocyanate reducing power assays). The DNA-protecting effect by EEPS was tested using pBR322 plasmid DNA against •OH radical-induced damage. The inhibition potentials of both extracts against several enzymes related to metabolic diseases (α-glucosidase, α-amylase, xanthine oxidase, and protease) were evaluated. The phytochemical analysis was conducted by an LC-QTOF-MS/MS technique. EEPS proved to be a better antioxidant and had higher phenolic content compared to WEPS. EEPS demonstrated a protective effect on DNA with recovery percentage linearly correlated with EEPS concentrations. Strong inhibition on α-glucosidase and α-amylase was observed for EEPS; however, EEPS and WEPS showed weak inhibitions on xanthine oxidase and protease. LC-QTOF-MS/MS analysis identified seven main components in EEPS, namely scroside E, forsythoside A and forsythoside B, lavandulifolioside, diosmin, nobilin D, campneoside I, and isoacteoside. These components may be responsible for the observed enzymes inhibitions and antioxidant properties. Premna serratifolia leaves can be an appropriate choice for the development of nutraceutical and drug preparations.

BACKGROUND: The leaf and fruit of Psidium guajava L. are potential for neutraceutical beverage especially for antidiabetic drink. The aims of this study were to determine the antidiabetic activity of aqueous extract of leaf (LE) and fruit (FE) from P. guajava.METHODS: Both extracts were investigated for their inhibitory effect on α-glucosidase activity in vitro. Their antioxidant activities were measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging, ferrous ion chelating, reducing power and phosphomolybdate methods.RESULTS: The IC50 of LE, FEandacarbose as a positive control were 5.67, 428.00 and 823.99 μg/mL, respectively. The enzyme kinetic analysis indicated that LE inhibited α-glucosidase in a competitive inhibition type, similar to that of acarbose. Both extracts showed antioxidant activities, with LE showed stronger activities than FE in all methods. In DPPH method, IC50 of LE and FE were 74.77 and 843.84 μg/mL respectively, compared to 53.24 and 21.36 μg/mL for reference antioxidants butylated hydroxytoluene (BHT) and ascorbic acid (AA), respectively. In ferrous ion chelating activity, the IC50 were 147.07 and 2105.05 μg/mL for LE and FE, whereas ethylenediaminetetraacetic acid (EDTA) as a control sample was 66.50 μg/mL. In reducing power and phosphomolybdate methods, at different concentrations, the activities of LE, FE, and standard compounds showed the following order: AA > BHT > LE > FE.CONCLUSION: LE from P. guajava exhibited excellent inhibitory activity against α-glucosidase. In addition, LE had better antioxidant acivities than FE. This study can recommend the aqueous extract from P. guajava as a promising candidate for neutraceutical drink for prediabetic and diabetic patients.KEYWORDS: antioxidant, aqueous extract, α-glucosidase inhibition, guava, Psidium guajava L.

Introduction: Leaves of Premna serratifolia L. (local name: arogo) is well known as food ingredient for fish/meat-based soup in Tentena, Indonesia. Evaluation of its bioactivities is needed. Objective: This study aimed to evaluate the α-glucosidase inhibitory and antioxidant activities of infusion and decoction of P. serratifolia leaves. Methods: The leaf samples were prepared by infusion and decoction and analysed for their α-glucosidase inhibitory and antioxidant activities, as well as total phenolic contents and LC-MS profiles. Results: The total phenolic content of the decoction was higher than the infusion. The UV spectra of both infusion and decoction showed peak at 325 nm and shoulder at 285 nm. Their LC-MS yielded one dominant component at 132 (100) m/z fragment, which was tentatively identified as caffeic acid. Both infusion and decoction extracts exhibited strong α-glucosidase inhibition with IC 50 of 4.27 and 0.046 µg GAE/ml, respectively. The IC 50 for DPPH scavenging activity of the infusion and decoction were similar; 6.82 and 7.28 μg GAE/ml, respectively. But the IC 50 of the infusion and decoction for ferrous ion chelating activities were different; 161.66 and 28.34 μg GAE/ ml, respectively. The α-glucosidase inhibitory and antioxidant activities were related to the phenolic content. Conclusion: The study concludes that both infusion and decoction of arogo leaves have antidiabetic effect and potential antioxidant activity. The decoction of the leaves may increase its antidiabetic capacity.