Effect of Ionic Strength, pH and Chemical Displacers on the Percentage Protein Binding of Protein-Bound Uremic Toxins

<b><i>Background and Objectives:</i></b> While trying to optimize the dialysis clearances of protein-bound uremic toxins (PBUTs), their percentage protein binding (% PB) is an important parameter. We evaluated the effects of ionic strength, pH change and chemical displacers on the dissociation of PBUTs from albumin in vitro. <b><i>Methods:</i></b> PBUTs, such as 3-Carboxy-4-methyl-5-propyl-2-furan-propanoic acid (CMPF), p-cresylsulfate (PCS), indoxyl sulfate (IS) and indole-3-acetic acid (IAA), were spiked with human serum albumin (HSA) solution prepared with different Nacl concentrations and pH values or in the presence of a series of chemical displacers. Ultrafiltration was performed to separate the free and bound fractions, and the % PB of each PBUT was calculated. <b><i>Results:</i></b> For all 4 compounds, their % PB decreased with increasing ionic strength, while only slight changes occurred when the pH of the test solution increased from pH 6.0 to pH 8.5; PCS, IS and 3-IAA were relatively easily dissociated from albumin by drug displacement, while CMPF was released from HSA by all studied drugs with difficulty; the PB % for CMPF, PCS, IS and 3-IAA decreased most remarkably in the presence of free fatty acids, such as oleic acid (41.73% for CMPF, 29.9% for PCS, 23.22% for IS, and 20.34% for 3-IAA) and linoleic acid (43.12% for CMPF, 16.65% for PCS, 29.99% for IS, and 16.29% for 3-IAA). <b><i>Conclusion:</i></b> The protein binding of PBUTs can be decreased by higher ionic strength, increased pH and the presence of some chemical displacers, including free fatty acids. Effective dialytic removal of PBUTs may be achieved by applying these methods jointly to blood-purification techniques.