Interaction of Human Serum Albumin with Indomethacin: Spectroscopic and Molecular Modeling Studies

In this work, the interaction between indomethacin (IM) and human serum albumin (HSA) under simulative physiological conditions was investigated by the methods of fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular modeling. The experiment results showed that the fluorescence quenching of HSA by IM was a result of the formation of an IM-HSA complex and the corresponding association constants (K-a) between IM and HSA at four different temperatures were determined according to the modified Stern-Volmer equation. The resulting thermodynamic parameters Delta G, Delta H, and Delta S at different temperatures indicate that the hydrophobic force plays a major role for IM-HSA association, but hydrogen bonds also could not be excluded. A molecular modeling study further confirmed the binding mode and indicated that the binding of IM to HSA primarily takes place in sub-domain IIA (site I). The conformational investigation showed that the presence of IM decreased the alpha-helical content of HSA and induced slight unfolding of the polypeptides of protein, which confirmed that some microenvironmental and conformational changes occur for HSA molecules.