Spectroscopic study on flavonoid-drug interactions: Competitive binding for human serum albumin between three flavonoid compounds and ticagrelor, a new antiplatelet drug

The effects of three kinds of flavonoids, quercetin, rutin and baicalin, on the binding of ticagrelor to human serum albumin (HSA) were systematically investigated using fluorescence, UV-vis absorption and circular dichroism (CD) spectroscopic techniques. The results indicated that ticagrelor strongly quenched the HSA fluorescence by the style of static quenching and non-radiation energy transferring as a result of the HSA-ticagrelor complex formation, while the presence of flavonoids could not change the quenching mechanism. Ticagrelor could spontaneously bind in site I on HSA with high affinity, and this binding process was mainly driven by both hydrophobic forces and hydrogen bonding. The significantly decreased binding affinity and the unchanged binding mode and distance between ticagrelor and HSA indicated that that flavonoids could compete against ticagrelor in site I, and baicalin was the most effective competitor. The conformation investigation of HSA further confirmed the flavonoid/ticagrelor competitive binding mechanism.