Intermolecular Interactions of Saxagliptin and Vildagliptin with Human Serum Albumin

The binding interactions between human serum albumin (HSA) and two anti-diabetic drugs, saxagliptin (SXG) and vildagliptin (VDG), are studied. Different approaches are adopted, including native fluorescence, synchronous fluorescence, UV-visible absorption, and Fourier-transform infrared (FTIR) analysis, in addition to molecular docking simulations. Moreover, the thermodynamic parameters of the interactions are determined at different temperatures. The obtained results indicate that the intrinsic fluorescence of HSA is quenched via a static mechanism. Values for the binding constant, K a , are 4.0 × 10 4 , 2.49 × 10 4 , and 2.42 × 10 4 L/mol for SXG, and 1.13 × 10 4 , 8.54 × 10 3 , and 7.15 × 10 3 L/mol for VDG at 298, 310, and 318 K, respectively. Evidence from competition experiments with site markers indicate that both SXG and VDG bind HSA primarily at or near site I of the protein. FTIR spectroscopy data indicate an alteration of the protein conformation in the presence of SXG or VDG. Indeed, the results of different spectroscopic analyses indicated that noticeable changes in the protein structure conformation occur following the addition of SXG or VDG.