Release of Uremic Retention Solutes from Protein Binding by Hypertonic Predilution Hemodiafiltration

Abstract

Protein-bound uremic retention solutes accumulate in patients suffering from chronic kidney disease, and the removal of these solutes by hemodialysis is hampered. Therefore, we developed a dialysis technique where the protein-bound uremic retention solutes are removed more efficiently under high ionic strength. Protein-bound uremic solutes such as phenylacetic acid, indoxyl sulfate, and p-cresyl sulfate were combined with plasma in the presence of increased ionic strength. The protein integrity of proteins and enzymatic activities were analyzed. In vitro dialysis of albumin solution was performed to investigate the clearance of the bound uremic retention solutes. In vitro hemodiafiltrations of human blood were performed to investigate the influence of increased ionic strength on blood cell survival. The protein-bound fraction of phenylacetic acid, indoxyl sulfate, and p-cresyl sulfate was significantly decreased from 59.4% ± 3.4%, 95.7% ± 0.6%, 96.9% ± 1.5% to 36.4% ± 3.7%, 87.8% ± 0.6%, and 90.8% ± 1.3%, respectively. The percentage of phenylacetic acid, indoxyl sulfate, and p-cresyl sulfate released from protein was 23.0% ± 5.7%, 7.9% ± 1.1%, and 6.1% ± 0.2%, respectively. The clearance during in vitro dialysis was increased by 13.1% ± 3.6%, 68.8% ± 15.1%, and 53.6% ± 10.2%, respectively. There was no difference in NaCl concentrations at the outlet of the dialyzer using isotonic and hypertonic solutions. In conclusion, this study forms the basis for establishing a novel therapeutic approach to remove protein-bound retention solutes.

Interaction of human serum albumin with uremic toxins: a thermodynamic study

“…However, Böhringer et al have recently demonstrated in an in vitro study that the fraction of uremic toxins was signi-cantly decreased through hypertonic predilution hemodial-tration. 16 This nding underscores clearly the importance of ionic strength for the binding of toxins to HSA.…”

“…The importance of this toxin derives from the fact that quantitative experiments using equilibrium dialysis (ED) and chromatographic methods have revealed a considerable amount of PhAA present in dialysis patients prior and aer dialysis. 6,14,16 Furthermore, in a high performance liquid chromatography experiment (HPLC), it has been shown that PhAA accumulation in CKD patients inhibits the expression of inducible nitric oxide synthase and therefore might contribute to the higher cardiovascular risk of these patients. 2 The importance of ionic contributions to the binding of this toxin is demonstrated in an in vitro study by Böhringer et al and forms the basis for establishing a more effective clearance of PhAA by raising the ionic strength.…”

“…2 The importance of ionic contributions to the binding of this toxin is demonstrated in an in vitro study by Böhringer et al and forms the basis for establishing a more effective clearance of PhAA by raising the ionic strength. 16 Certainly, the binding behavior in an in vivo environment of blood plasma is more a complex process where the specic binding mechanisms cannot be identied anymore.…”

“…This is a plausible explanation for the results obtained recently by Jankowski et al who measured almost a doubling of released PhAA during hypertonic predilution hemodialtration. 16 Furthermore, we have shown in previous studies, that ionic strength does contribute signi-cantly towards charge-charge interaction between protein and a short polyelectrolyte. Table 1).…”

“…[15][16][17] For this purpose an improved thermodynamic understanding of the interaction of toxins with HSA is absolutely necessary.…”