Study on the Competitive Binding of Food Ingredients and Gambogic Acid to Plasma Proteins: Insights From Spectroscopy, Docking, and Cell Assay

Human serum albumin (HSA) is the most abundant protein in plasma and an important transporter of exogenous small molecules. In this paper, the binary interaction of HSA with gambogic acid (GA), theophylline (TP), and quercetin (QC) and the ternary interaction of the HSA-QC system in the presence of food components were studied. Fluorescence emission and UV-Vis absorption spectra analysis showed that all three compounds bind HSA via a static quenching model. Competition binding site analysis and molecular docking revealed they bind to HSA Site I. The presence of TP or QC preferentially occupied GA's binding site, significantly decreasing the GA-HSA binding constant and affecting the HSA-GA binary system. In vitro cell experiments validated that TP/QC increase GA's free concentration, and both enhance GA's inhibitory effect on HepG2 cells in the presence of plasma proteins. Synchronous fluorescence, 3D fluorescence, and circular dichroism (CD) spectroscopy indicated TP/QC influence GA-induced conformational changes in HSA, with TP having a significantly greater impact than QC. This study offers new insights into GA's interactions with food components and provides dietary recommendations for clinical GA use.