Diosgenin from <i>Dioscorea bulbifera</i>: Novel Hit for Treatment of Type II Diabetes Mellitus with Inhibitory Activity against α-Amylase and α-Glucosidase

<div><p>Diabetes mellitus is a multifactorial metabolic disease characterized by post-prandial hyperglycemia (PPHG). α-amylase and α-glucosidase inhibitors aim to explore novel therapeutic agents. Herein we report the promises of <i>Dioscorea bulbifera</i> and its bioactive principle, diosgenin as novel α-amylase and α-glucosidase inhibitor. Among petroleum ether, ethyl acetate, methanol and 70% ethanol (v/v) extracts of bulbs of <i>D. bulbifera</i>, ethyl acetate extract showed highest inhibition upto 72.06 ± 0.51% and 82.64 ± 2.32% against α-amylase and α-glucosidase respectively. GC-TOF-MS analysis of ethyl acetate extract indicated presence of high diosgenin content. Diosgenin was isolated and identified by FTIR, ¹H NMR and ¹³C NMR and confirmed by HPLC which showed an α-amylase and α-glucosidase inhibition upto 70.94 ± 1.24% and 81.71 ± 3.39%, respectively. Kinetic studies confirmed the uncompetitive mode of binding of diosgenin to α-amylase indicated by lowering of both Km and Vm. Interaction studies revealed the quenching of intrinsic fluorescence of α-amylase in presence of diosgenin. Similarly, circular dichroism spectrometry showed diminished negative humped peaks at 208 nm and 222 nm. Molecular docking indicated hydrogen bonding between carboxyl group of Asp300, while hydrophobic interactions between Tyr62, Trp58, Trp59, Val163, His305 and Gln63 residues of α-amylase. Diosgenin interacted with two catalytic residues (Asp352 and Glu411) from α-glucosidase. This is the first report of its kind that provides an intense scientific rationale for use of diosgenin as novel drug candidate for type II diabetes mellitus.</p></div

Kinetic analysis of porcine pancreatic α-amylase inhibition by isolated compound D by Lineweaver–Burk plot with starch as substrate.

<p>Kinetic analysis of porcine pancreatic α-amylase inhibition by isolated compound D by Lineweaver–Burk plot with starch as substrate.</p

Binding of diosgenin to α-glucosidase active pocket.

<p>(a) Depicts docked conformation of diosgenin with yeast alpha glucosidase (3AXI.pdb), (b) hydrogen bonding and hydrophobic interactions from alpha glucosidase-diosgenin inhibitor complex.</p

Quenching of intrinsic fluorescence of porcine pancreatic α-amylase bound to isolated compound D.

<p>Quenching of intrinsic fluorescence of porcine pancreatic α-amylase bound to isolated compound D.</p

Percent <i>α</i>-amylase inhibition by plant extracts and isolated compound D.

<p>Acarbose is taken as standard inhibitor. The data is indicated as the mean SEM; [<i>n</i>  =  3].</p

Binding of diosgenin to α-amylase active pocket.

<p>(a) Depicts docked conformation of diosgenin with porcine pancreatic α-amylase (1OSE.pdb), (b) hydrogen bonding and hydrophobic interactions from α-amylase and diosgenin inhibitor complex.</p

Characterization of purified compound D.

<p>HPLC profiles of standard diosgenin and isolated compound D exhibiting α-amylase and α-glucosidase inhibition. Inset left panel: HPTLC analysis of A) crude ethyl acetate extract of <i>D. bulbifera</i> bulb; B) isolated compound D and C) standard diosgenin. Inset right panel: Stereochemical structure of compound D as elucidated by NMR analysis identified as diosgenin.</p

Percent crude murine pancreatic amylase inhibition by plant extracts and isolated compound D.

<p>Acarbose is taken as standard inhibitor. The data is indicated as the mean SEM; [<i>n</i>  =  3].</p

CD spectra of porcine pancreatic α-amylase bound with isolated compound D.

<p>CD spectra of porcine pancreatic α-amylase bound with isolated compound D.</p

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