α-Amylase Inhibitory Secondary Metabolites from Artemisia pallens Wall ex DC – Biochemical and Docking Studies

Diabetes Mellitus Type-2 (DM-2) has become a challenging disease worldwide as many young adults are also getting affected by it due sedentary lifestyle and wrong diets. Multiple studies have shown that control over α-amylase enzyme in gut could be a better approach to treat DM-2. The secondary metabolites produced by the plants have various biological properties and many are used as drugs. In the current study, we isolated secondary metabolites from acetone leaf extracts of Artemisia pallens Wall ex DC (Family: Asteraceae) and tested them for their porcine pancreatic α-amylase (PPA) inhibitory activity in vitro and in silico. This extract exhibited good PPA inhibition, with IC₅₀ value of 388.05 µg/ml. The IC₅₀ value of Acarbose (a known pancreatic α-amylase inhibitor drug / positive control) was 9.71 µg/ml. Various secondary metabolites detected from acetone leaf extract by LC-MS analysis, were used for the molecular docking studies using AutoDock 4.2.6. The co-crystallised structure of PPA and Acarbose was retrieved from Protein Data Bank (PDB ID: 1OSE). The binding energies of few metabolites were (kcal/mol): Isoquercetin (-11.57), Cryptochlorogenic Acid (-11.17), Cirsilineol (-10.24), Kaempferide (-9.99), Fustin (-9.86), 6- Demetroxycapillarisin (-9.82), Piperine (-9.45), Ergometrine (-9.43), Apigenin (-9.38) & Artemisinin (-9.27). Acarbose had a binding energy of -17.58 kcal/mol. All the metabolites looked highly promising as α-amylase inhibitors and most of them interacted with PPA via hydrogen bonding with crucial amino acid residues: ASP197, ASP300 & GLU233. Thus the acetone extract of A. pallens leaves can potentially inhibit PPA (strong amino acid sequence similarity with human pancreatic α-amylase) and hence extrapolation of these inhibitory results could be valid for human pancreatic α-amylase as well.