Potent α-amylase inhibitory activity of Indian Ayurvedic medicinal plants

Background: Indian medicinal plants used in the Ayurvedic traditional system to treat diabetes are a valuable source of novel anti-diabetic agents. Pancreatic alpha-amylase inhibitors offer an effective strategy to lower the levels of post-prandial hyperglycemia via control of starch breakdown. In this study, seventeen Indian medicinal plants with known hypoglycemic properties were subjected to sequential solvent extraction and tested for alpha-amylase inhibition, in order to assess and evaluate their inhibitory potential on PPA (porcine pancreatic alpha-amylase). Preliminary phytochemical analysis of the lead extracts was performed in order to determine the probable constituents. Methods: Analysis of the 126 extracts, obtained from 17 plants (Aloe vera (L.) Burm. f., Adansonia digitata L., Allium sativum L., Casia fistula L., Catharanthus roseus (L.) G. Don., Cinnamomum verum Persl., Coccinia grandis (L.) Voigt., Linum usitatisumum L., Mangifera indica L., Morus alba L., Nerium oleander L., Ocimum tenuiflorum L., Piper nigrum L., Terminalia chebula Retz., Tinospora cordifolia (Willd.) Miers., Trigonella foenum-graceum L., Zingiber officinale Rosc.) for PPA inhibition was initially performed qualitatively by starch-iodine colour assay. The lead extracts were further quantified with respect to PPA inhibition using the chromogenic DNSA (3, 5-dinitrosalicylic acid) method. Phytochemical constituents of the extracts exhibiting >= 50% inhibition were analysed qualitatively as well as by GC-MS (Gas chromatography-Mass spectrometry). Results: Of the 126 extracts obtained from 17 plants, 17 extracts exhibited PPA inhibitory potential to varying degrees (10%-60.5%) while 4 extracts showed low inhibition (< 10%). However, strong porcine pancreatic amylase inhibitory activity (> 50%) was obtained with 3 isopropanol extracts. All these 3 extracts exhibited concentration dependent inhibition with IC50 values, viz., seeds of Linum usitatisumum (540 mu gml(-1)), leaves of Morus alba (1440 mu gml(-1)) and Ocimum tenuiflorum (8.9 mu gml(-1)). Acarbose as the standard inhibitor exhibited an IC50 (half maximal inhibitory concentration) value of 10.2 mu gml(-1). Phytochemical analysis revealed the presence of alkaloids, tannins, cardiac glycosides, flavonoids, saponins and steroids with the major phytoconstituents being identified by GC-MS. Conclusions: This study endorses the use of these plants for further studies to determine their potential for type 2 diabetes management. Results suggests that extracts of Linum usitatisumum, Morus alba and Ocimum tenuiflorum act effectively as PPA inhibitors leading to a reduction in starch hydrolysis and hence eventually to lowered glucose levels.