Spectroscopic and thermodynamic studies of the binding mechanism of metformin to pepsin

Abstract Metformin belongs to biguanide class of compound and is an approved drug for the treatment of type II diabetes. Besides, metformin can prevent the occurrence of other diseased conditions like cardiovascular disease, polycystic ovary syndrome, etc. There are various side effects associated with oral ingestion of metformin. Some of these effects may occur due to its interaction with digestive enzymes like pepsin. Therefore, in the present study, binding mechanism of pepsin with metformin was investigated using biophysical and molecular modeling methods. The fluorescence quenching study shows that metformin quenches the fluorescence of pepsin essentially through static quenching and binding forces were non-covalent in nature. Binding of metformin induced alteration in the conformation of pepsin was confirmed using circular dichroism technique. Isothermal titration calorimetric measurements revealed two binding sites of metformin to the pepsin and the binding is essentially enthalpy driven. Van der Waals interactions and hydrogen bonding forces have dominated the binding interactions. This was further substantiating using molecular docking. Finally, in vitro assay suggested that metformin reduced 75% pepsin activity under physiological conditions.