Planta Med 2015; 81 - PW_100
DOI: 10.1055/s-0035-1565724

Inhibitory potential of 40 medicinal plant extracts from Madagascar against enzymes linked to type 2 diabetes

MN Beidokhti 1, D Staerk 1, AK Jåger 1, ES Lobbens 2, P Rasoavaivo 3
  • 1Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
  • 2Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
  • 3Institut Malgache de Recherches Appliques, University of Antananarivo, Madagascar

Worldwide, type 2 diabetes affects 246 million people. Management of blood glucose by inhibition of carbohydrate-hydrolyzing enzymes is important to avoid diabetic complications. The aim of this study was to assess whether inhibition of α-glucosidase [1] and α-amylase [2] by ethanol extracts of 40 Madagascarian plants is the scientific rationale behind their traditional anti-diabetic use.

The ethanolic extracts were generally inactive against pancreatic α-amylase, and only bark extracts of Psidium guajava and Vangueria madagascariensis showed good activity with IC50 of 10.6 and 11.6 µg/mL, respectively. Several extracts showed strong inhibition of yeast α-glucosidase. Psidium guajava bark and leaf extracts showed IC50 of 0.5 and 1.0 µg/mL, respectively. Bark extract of Antidesma madagascariensis showed IC50 of 1.7 µg/mL, whereas bark extract of Vangueria madagascariensis and leaf extract of Rhizophora sp. showed an IC50 of 1.8 µg/mL.

All extracts with IC50 below 12.6 µg/mL were investigated for their content of tannins, known to give false-positive results in enzyme-based in vitro assays due to their non-specific enzyme binding. All active extracts had large amounts of tannins in the HPLC chromatogram, except aerial parts of Euphorbia hirta and leaves of Artocarpus heterophylla, Ravenala madagascariensis and Zanthoxylum tsihanimposa, which contained only low levels of tannins. These four species were subjected to high-resolution α-glucosidase bioactivity profiling [2], in order to determine whether they contained specific enzyme inhibitors. It was, however, found that the α-glucosidase inhibitory profile correlated fully with the elution profile of the tannins.

In conclusion, the 40 plant species traditionally used on Madagascar to treat diabetes do not hold promise as specific inhibitors of the carbohydrate-hydrolyzing enzymes α-amylase and α-glucosidase.

References:

[1]Schmidt JS et al. Food Chem 2012; 135: 1692 – 99

[2] Okutan L et al. J Agric Food Chem 2014; 62: 11465 – 71