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

Abstract

Background and Objectives: 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. Methods: 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. Results: 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). Conclusion: 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.

Improved Dialysis Removal of Protein-Bound Uraemic Toxins with a Combined Displacement and Adsorption Technique

“…To adjust to the main ingredients of ω-6 soybean oil-based lipid emulsion (Intralipid TM ), FAs were prepared by mixing oleic acid and linoleic acid ([linoleic acid]/[oleic acid] = 2) at a final concentration of 1 mmol/L in the inlet blood line of the in vitro HD model based on the established preliminary data [36, 37]. As conformed previously, CMPF, which possesses the highest binding affinity to HSA among the PBUTs tested in the study, was undetectable in the standard bicarbonate dialysate of the control group.…”

“…In a recent study, we chose CMPF as a representative with high binding affinity at site I of HSA as well as PCS and IS as prototypes tightly binding at site II of HSA. Then, we evaluated the effects of higher ionic strength, pH change, and different Alb displacers on the dissociation of these PBUTs from Alb simultaneously in vitro [36]. Results showed that the inhibitory effects were more remarkable with the addition of binding competitors than that of ionic strength and pH changes.…”

“…The specifications of the minidialyser and the HD setup have been previously described [31]. In vitro, 2 long-chain FA mixtures, prepared by mixing oleic acid and linoleic acid ([linoleic acid]/[oleic acid] = 2), were selected as binding competitors to displace PBUTs from Alb according to preliminary experiments [36, 37]. In vivo, we compared the removal capacity of displacement and adsorption techniques using Intralipid TM infusion in the blood side and Alb-rich dialysate in the dialysate side, respectively.…”

The Interplay between Uremic Toxins and Albumin, Membrane Transporters and Drug Interaction

“…Shi et al (2019) studied the effects of ionic strength, pH, and chemical displacers on the percentage protein binding (PB) of PBUTs, showing that the PB% decreased with increasing ionic strength, but only a few changes occurred with the increased pH (6.0 to 8.5) [ 67 ]. Regarding chemical displacers, they studied ibuprofen, warfarin, phenylbutazone, indomethacin, furosemide, oleic acid, linoleic acid, and docosahexaenoic acid (DHA), which are known to be typical displacers of HSA sites I or II.…”

Cardiorenal syndrome: Multi‐organ dysfunction involving the heart, kidney and vasculature

“…Addition of nanoporous sorbents on the dialysis membrane was shown to increase protein‐bound uraemic toxin removal in a laboratory‐based study (Pavlenko et al, 2017). Reducing protein‐bound uraemic toxin protein binding by increasing blood ionic strength and pH in blood‐purification strategies may be viable options according to in vitro validations (Krieter et al, 2017; Shi et al, 2019). Similarly, competitive binding via chemical displacers is another feasible avenue (Madero et al, 2019; Tao et al, 2016).…”