Binding studies of costunolide and dehydrocostuslactone with HSA by spectroscopy and atomic force microscopy

Human serum albumin (HSA), a major plasma protein and plasma-derived therapeutic, interacts with a wide variety of drugs and native plasma metabolites. In this study the interactions of costunolide (CE) and dehydrocostuslactone (DE) with HSA were investigated by molecule modeling, atomic force microscopy (AFM), and different optical techniques. In the mechanism discussion, it was proved that fluorescence quenching of HSA by both of the drugs is a result of the formation of drug–HSA complexes. Binding parameters for the reactions were determined according to the Stern–Volmer equation and static quenching. The results of thermodynamic parameters ΔG0, ΔH0, and ΔS0 at different temperatures indicated that hydrogen bonding interactions play a major role in the drug–HSA associations process. The binding properties were further studied by quantitative analysis of CD, FTIR, and Raman spectra. Furthermore, AFM results showed that the dimension of HSA molecules became more swollen after binding with the drugs.