Structure and binding properties of serum albumin in uremic patients at different periods of hemodialysis.

Few diagnostic methods are available that describe uremia related changes of the albumin molecule structure in hemodialysis patients. The impaired human serum albumin (HSA) function is an essential part of the uremic syndrome and probably influences the long-term outcome of patients on maintenance dialysis. The albumin binding capacity (characterized for different binding centers on the molecule) is one of the relevant clinical parameters. During the current study, marker substances were utilized to evaluate center-specific binding capacity. Patients were divided into 3 groups depending on the time on hemodialysis (HD) treatment (in years) with healthy blood donors as control. Compared to healthy persons, results demonstrate a considerable impairment of binding characteristics in HD patients. Only in patients on maintenance HD for more than 5 years did ligand binding properties improve significantly. A correlation between the time of chronic HD and the recovery in binding capacity was found for the majority of binding centers of the HSA molecule. Similar results were seen applying such analytical methods as thermography (melting points) and thermofluorescence. Binding capacity impairment found for specified binding centers on the HSA molecule as the main serum carrier protein may have a direct impact on different clinical situations and the HD long-term outcome.

Biophysical studies on the correction of uremic human serum albumin binding defects by in vitro charcoal adsorption treatment.

Spectrofluorimetry, flow microcalorimetry, and differential scanning microcalorimetry (DSMC) were used to study the conformation, binding function, and ligand loading of uremic albumin obtained from the blood plasma of 2 end-stage renal disease (ESRD) patients before and after charcoal plasma treatment at different pH values (3.0-9.0). The spectrofluorimetric patterns of conformational N-F transition at low pH (4.2-3.5) are practically identical for both samples of uremic human serum albumin (HSA) and control HSA from healthy donors. After the charcoal treatment at pH 3.0 and 4.0, the enthalpies of complexing on uremic HSA with bromsulfalein and sodium dodecylsulfate approach that of donor HSA. The binding affinity of uremic HSA for sodium octanoate, phenol red, and salicylic acid following low pH charcoal treatment even exceed those of donor HSA. At the same time the charcoal treatment of uremic plasma at neutral and alkaline pH does not notably improve the binding characteristics of isolated HSA. Adsorption at low pH values completely restores the tryptophan fluorescence spectrum position of uremic albumin and improves the thermodynamic characteristics of its melting process. Using DSMC data, it can nevertheless be concluded that some conformational changes or a certain amount of high-affinity bound endogenous ligands still remain after low pH uremic HSA purification. The latter conclusion requires additional improvements of adsorption treatment of uremic plasma.