Deciphering the Inactivation of Human Pancreatic α-Amylase, an Antidiabetic Target, by Bisdemethoxycurcumin, a Small Molecule Inhibitor, Isolated from Curcuma longa

Natural products from plants are an excellent source of Human pancreatic α-amylase (HPA) inhibitors which have therapeutic application as oral agents to control blood glucose levels. The mechanism of action by Bisdemethoxycurcumin (BDMC) has been reported, isolated from Curcuma longa rhizomes, which inactivates HPA, a target for type-2 diabetes. This study validates its mode of action and its target which has to date remained largely unknown. The cytotoxicity and bioactivity of crude extract and BDMC on the pancreatic acinar AR42J secretory model cell line were evaluated with LD50 value of 16.25 μg ml-1 and 63.53 μM, and secretory α-amylase inhibition of 41% and 30%, respectively. BDMC uncompetitively inhibits HPA (Ki' of 10.1μM) and a binding affinity (Ka) of 8.5 x 104 M-1 with the involvement of surface exposed aromatic residues. The thermodynamic parameters suggest that binding is both enthalpically and entropically driven with ΔGº of - 28.13 kJ mol-1. Computational ligand docking showed that inactivation depends on hydrogen bonding and π-π interactions. Thus, BDMC, a natural product could be lowering post-prandial glycemia via a novel mode of binding and inactivation of HPA and may proved to be a good drug candidate to reduce/control post-prandial hyperglycemia.