Characterization of Interactions Between Fluoroquinolones and Human Serum Albumin by CE–Frontal Analysis

Abstract

The binding of fluoroquinolones to the transport protein, human serum albumin (HSA), under simulated physiological conditions has been studied by capillary electrophoresis–frontal analysis (CE–FA). The binding of these drugs to human plasma was evaluated by using ultrafiltration and capillary electrophoresis. The free drug concentration [D]_f at each HSA concentration was determined by the plateau height in the electropherograms and the calibration lines. The binding constants of fluoroquinolones and HSA were estimated using nonlinear regression with origin 7.5 software. The fluoroquinolones were found to show low affinity toward HSA, with binding constants ranging from 1.73 × 10² to 5.40 × 10² M⁻¹. The percentages of protein binding (PB) for fluoroquinolones to HSA were between 8.6 and 22.2%, while the PB percentages for fluoroquinolones to human plasma were between 10.2 and 33.1%. It can be found that the PB percentages for fluoroquinolones to HSA are mostly lower than those for fluoroquinolones to human plasma. It suggests that HSA is the primary protein responsible for the binding of fluoroquinolones in human plasma. The thermodynamic parameters were obtained by CE–FA. The positive ∆H and ∆S values obtained by CE–FA showed that the binding reaction was an endothermic process, and the entropy drive the binding and hydrophobic interaction played major roles in the binding of fluoroquinolones to HSA.