Evaluation of traditional Indian antidiabetic medicinal plants for human pancreatic amylase inhibitory effect in vitro

Abstract

Pancreatic α-amylase inhibitors offer an effective strategy to lower the levels of post prandial hyperglycemia via control of starch breakdown. Eleven Ayurvedic Indian medicinal plants with known hypoglycemic properties were subjected to sequential solvent extraction and tested for α-amylase inhibition, in order to assess and evaluate their inhibitory potential on pancreatic α-amylase. Analysis of 91 extracts, showed that 10 exhibited strong Human Pancreatic Amylase (HPA) inhibitory potential. Of these, 6 extracts showed concentration dependent inhibition with IC(50) values, namely, cold and hot water extracts from Ficus bengalensis bark (4.4 and 125 μgmL(-1)), Syzygium cumini seeds (42.1 and 4.1 μgmL(-1)), isopropanol extracts of Cinnamomum verum leaves (1.0 μgmL(-1)) and Curcuma longa rhizome (0.16 μgmL(-1)). The other 4 extracts exhibited concentration independent inhibition, namely, methanol extract of Bixa orellana leaves (49 μgmL(-1)), isopropanol extract from Murraya koenigii leaves (127 μgmL(-1)), acetone extracts from C. longa rhizome (7.4 μgmL(-1)) and Tribulus terrestris seeds (511 μgmL(-1)). Thus, the probable mechanism of action of the above fractions is due to their inhibitory action on HPA, thereby reducing the rate of starch hydrolysis leading to lowered glucose levels. Phytochemical analysis revealed the presence of alkaloids, proteins, tannins, cardiac glycosides, flavonoids, saponins and steroids as probable inhibitory compounds.

Figure 1

The percent relative enzyme activity (RA %) of porcine pancreatic α-amylase (PPA) on inhibition with different extracts. (a) Cold-water extracts (CWE). (b) Hot-water extracts (HWE). (c) Methanol extracts (ME). (d) Isopropanol extracts (IP). (e) Acetone extracts (AE) of the listed plants. Pure porcine pancreatic α-amylase serves as control. The data is indicated as the mean ± SEM; (n = 3). The students F-test was used and the bars with different asterisks (***, **, *) show significant difference with respect to control (P <  .05).

Figure 2

IC₅₀ values of the extracts exhibiting ≥50% inhibition on Porcine pancreatic α-amylase and Human pancreatic α-amylase enzyme activity. The data is calculated as the mean ± SEM; (n = 3). The students F-test was used and the bars with different asterisks (***, **, *) show significant difference with respect to control (P  <  .05). Acarbose is taken as the standard α-amylase inhibitor.

Figure 3

Human Pancreatic α-amylase inhibition (%) of different extracts at varying concentrations. The data is indicated as the mean ± SEM; (n = 3). (P <  .05).

Figure 4

Lineweaver-Burk Plot of extracts exhibiting concentration independent inhibition on Human pancreatic α-amylase enzyme activity. The data is indicated as the mean ± SEM; (n = 3); (P <  .05).

Figure 5

Pancreatic α-amylase inhibition by Indian medicinal plant extracts as a potential antidiabetes mechanism. Double bar marks (∖ ∖) indicate inhibition of amylase activity leading to a reduction of maltose, oligosaccharide and glucose concentration. ME: Methanol extract; AE: Acetone extract; IPE: Isopropanol extract; CWE: Cold-water extract; HWE: Hot-water extract.