The fluorescence signal of albumin-bound bilirubin to monitor drug-induced bilirubin displacement from human serum albumin

Abstract

Bilirubin (BR) binding to human serum albumin (HSA) may be affected by drugs, which may cause hyperbilirubinemia. A new method is proposed to investigate BR displacement from HSA using the characteristic fluorescence signal of albumin-bound BR at 533 nm upon 460 nm excitation. Any decrease in the fluorescence intensity at 533 nm upon drug addiction is direct evidence of BR displacement. Drug-induced BR displacement was tested using the well-known drug markers, warfarin (WFN) for Site I, ketoprofen (KTN) for Site II and hemin (HMN) for Site III of HSA. The maximum quenching (93%) and the highest Ka value (1.13 × 105 M1), obtained with HMN, suggested a common binding site of BR and HMN. Relatively lower BR displacement by WFN and KTN and lowered Ka values can be attributed to allosteric phenomena. These results showed the importance of the albumin-bound BR fluorescence signal in testing BR displacement from albumin.