Protein tyrosine phosphatase 1B and α-glucosidase inhibitory activities of Pueraria lobata root and its constituents

Ethnopharmacological relevance: Pueraria lobata root was used to treat wasting-thirst regarded as diabetes mellitus and was included in the composition of Okcheonsan, which is prescribed for thirst-waste in traditional Chinese medicine. Aim of the study: The objective of this study was to evaluate the anti-diabetic potential of the root of Pueraria lobata and its constituents via protein tyrosine phosphatase 1B (PTP1B) and alpha-glucosidase inhibitory activities. Materials and methods: In this study, anti-diabetic activities of the 70% ethanolic (EtOH) extract from P. lobata roots and its solvent soluble fractions with the isolated compounds were investigated by evaluating in vitro PTP1B and alpha-glucosidase inhibitory activities. We also examined the potentials of active compounds as PTP1B and alpha-glucosidase inhibitors via enzyme kinetics and in silico molecular docking simulation between the enzymes and active compounds. Results: Triterpenoids lupeol and lupenone were potent PTP1B inhibitors with IC50 values of 38.89 +/- 0.17 and 15.11 +/- 1.23 mu M. Kinetic study using the Lineweaver-Burk and Dixon plots demonstrated that these compounds showed a noncompetitive-type inhibition against PTP1B with respective K-i values of 13.88 mu M and 21.24 mu M. In addition, molecular docking simulation showed lupeol and lupenone has negative binding energy values of -8.03 and -8.56 kcal/mol. Considering the alpha-glucosidase inhibitory potential, daidzein, genistein, and calycosin exhibited the most potent alpha-glucosidase inhibition with IC50 values of 8.58 +/- 0.94, 2.37 +/- 0.52 and 6.84 +/- 1.58 mu M, respectively. Kinetic study demonstrated that these 3 compounds showed a noncompetitive-type inhibition against alpha-glucosidase with respective K-i values of 17.64 mu M, 5.03 mu M and 13.83 mu M. Moreover, molecular docking simulation showed daidzein, genistein and calycosin has more lower binding energy (-7.16 kcal/mol, -7.42 kcal/mol and -7.31 kcal/mol) with higher binding affinity and tight binding capacity in the molecular docking studies than standard ligand alpha-D-glucose (-6.74 kcal/mol). Conclusion: Our results of the present study clearly demonstrate the potential of P. lobata extract and its constituents to inhibit PTP1B and alpha-glucosidase, contributing to the development of therapeutic or preventive agents that can be used in the treatment of diabetes.