INHIBITORY POTENCY OF WITHANIA SOMNIFERA EXTRACTS AGAINST DPP-4: AN IN VITRO EVALUATION

Background: Pharmacologic treatments for type 2 diabetes are based upon increasing insulin availability and improving sensitivity to insulin. Nowadays, glucagon like peptide-1 (GLP-1) based therapies aims at glucose control through DPP-4 inhibitors. DPP-4 is a transmembrane glycoprotein belongs to prolyl oligopeptidase family, with the specificity of removing X-Pro or X-Ala dipeptides from the N-terminus of polypeptides. GLP-1 effect by stimulating glucose-dependent insulin release from the pancreatic islets, inhibit inappropriate post-meal glucagon release and slow gastric emptying promoting leaky gut. The current study investigated DPP-4 inhibitory activity of catechin, isolated from Withania somnifera (WS), for ethnopharmacological treatment of type 2 diabetes and aimed to increase availability of GLP-1and sensitivity to insulin. Materials and Methods: Young and matured fresh roots, leaves, and fruits of WS plant extract were considered and were systematically evaluated for DPP-4 inhibitory activity using in vitro method, enzyme kinetics, phytochemical analysis, RP-HPLC, LCMS and 1H and 13C NMR method and structure-activity relationship (SAR) studies. Results: In this study, methanol (100% and 80%) extracts of WS matured root exhibited maximum DPP-4 inhibitory activity when compared to other extracts. The maximum DPP-4 inhibitory activity was found in 100% methanol extract of matured root. Phytobioactive was purified by RP-HPLC. The compound purified was found to be flavonoid and was characterized (LCMS, 1H and 13C NMR studies), identified as catechin. Auxiliary, molecular docking was performed using Ligand Fit method using PatchDock package. The study revealed the binding affinity of catechin with DPP-4 to be -6.601 kcal/mol with 13 hydrogen interactions with the receptor and was very similar to the standard potent blockers withaferin A and others (cuscohygrine, scopoletin, sitoindoside IV, tropine), further confirming its hyperglycemic potency. Conclusion: The study reveals that, 100% methanol extract of WS matured roots contains the compound- catechin, which exhibits DPP-4 inhibitory activity resulting in increased level of bioactive GLP-1 and GIP. In this background, we concluded that the WS will be a better source for further development as new antidiabetic drugs.