title: Screening for potential α-glucosidase and α-amylase inhibitory constituents from selected Vietnamese plants used to treat type 2 diabetes.
abstract: BACKGROUND
  The 18 plant species investigated in this study have been used as herbal antidiabetic remedies in Vietnamese traditional medicines. This study aimed to evaluate their ability to inhibit α-glucosidase and α-amylase, two key enzymes involved in serum glucose regulation.
  
  
  METHODS
  Chloroform, ethanol and water extracts of 18 plants were screened for α-glucosidase and α-amylase inhibitory activity. Analytical-scale HPLC was subsequently used to investigate the most active extracts, where samples with low level of tannins were identified and fractionated into 96-well microplates, followed by α-glucosidase and α-amylase assessment of each well. High-resolution α-glucosidase and α-amylase inhibition profiles constructed from these assays allowed identification of HPLC peaks correlated with α-glucosidase and α-amylase inhibitory activity. The active constituents were subsequently isolated using preparative-scale HPLC and their structure was elucidated by HR-ESIMS and NMR.
  
  
  RESULTS
  Ethanol extracts of Nepenthes mirabilis, Phyllanthus urinaria, and Kandelia candel significantly inhibited α-glucosidase with IC50 values of 32.7±6.3, 39.7±9.7, and 35.4±13.9μg/mL, respectively. Water extracts of N. mirabilis, Phyllanthus amarus, P. urinaria, Lagerstroemia speciosa, Syzygium cumini, Rhizophora mucronata, and K. candel showed IC50 values of 3.3±0.8, 34.9±1.5, 14.6±4.6, 5.4±0.5, 20.9±1.8, 3.3±0.6, and 4.0±0.8μg/mL, respectively. In the α-amylase inhibition assay, ethanol extracts of K. candel and Ficus racemosa showed IC50 of 7.6±0.9 and 46.7±23.6μg/mL, respectively. Showing low tannin constituents as seen from HPLC profiles, P. amarus and P. urinaria water extracts and F. racemosa ethanol extract were subjected to microfractionation. Only high-resolution α-glucosidase inhibition profiles of P. amarus and P. urinaria water extracts showed several active compounds, which were isolated and identified as corilagin (1), repandusinic acid A (2), and mallotinin (3). IC50 of these compounds were 1.70±0.03, 6.10±0.10, and 3.76±0.15μM, respectively. Kinetics analysis revealed that 1 displayed a mixed type mode of inhibition with Ki and Ki' values of 2.37±0.90 and 2.61±0.61μM, respectively, whereas 2 and 3 competitively inhibited α-glucosidase with Ki values of 4.01±0.47 and 0.65±0.11μM, respectively.
  
  
  CONCLUSIONS
  Corilagin (1), repandusinic acid A (2), and mallotinin (3) were potent α-glucosidase inhibitors contributing significantly to the inhibitory effect observed for the water extracts of P. amarus and P. urinaria.
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Binh T D
authors.initials: BTD
authors.lastname: Trinh
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Dan
authors.initials: D
authors.lastname: Staerk
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark. Electronic address: anna.jager@sund.ku.dk.
authors.forename: Anna K
authors.initials: AK
authors.lastname: Jäger
mesh_terms: D001578:Benzopyrans / Q000737:chemistry / Q000494:pharmacology; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy*; D005947:Glucose / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D005960:Glucosides / Q000737:chemistry / Q000494:pharmacology; D065089:Glycoside Hydrolase Inhibitors / Q000494:pharmacology*; D006801:Humans; D047348:Hydrolyzable Tannins / Q000737:chemistry / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000737:chemistry / Q000494:pharmacology; D008519:Medicine, Traditional; D015394:Molecular Structure; D010936:Plant Extracts / Q000008:administration & dosage / Q000627:therapeutic use*; D010946:Plants, Medicinal / Q000737:chemistry*; D014744:Vietnam; D000516:alpha-Amylases / Q000037:antagonists & inhibitors*; D000520:alpha-Glucosidases / Q000378:metabolism*
chemical_list: D001578:Benzopyrans; D005960:Glucosides; D065089:Glycoside Hydrolase Inhibitors; D047348:Hydrolyzable Tannins; D007004:Hypoglycemic Agents; D010936:Plant Extracts; C079484:repandusinic acid A; C049096:corilagin; D000516:alpha-Amylases; D000520:alpha-Glucosidases; D005947:Glucose
keywords: High-resolution inhibition profile; Phyllanthus; Type 2 diabetes; Vietnamese plants; α-amylase; α-glucosidase