Extraction of uraemic toxins with activated carbon restores the functional properties of albumin.

BACKGROUND: Previous work has demonstrated that a partial normalization of the conformation of albumin from uraemic plasma and a substantial restoration of its binding abilities can be achieved by extraction with activated charcoal. This is best achieved at pH 3, but exposure of whole plasma to this low pH leads to the loss of some essential components. METHODS: The melting curves and ligand-binding abilities of uraemic albumin have been investigated after extraction with a new generation of activated carbon at three pH values (7.2, 3.0 and 5.08). RESULTS: Albumin isolated from uraemic plasma had a characteristically increased melting temperature because of bound ligands. Extraction of uraemic plasma at pH 7.2, 5.08 and 3.0 induced low-temperature shifts of albumin thermo-adsorption maximum T1 of 1.4, 3.8, 2.4 degrees C and T2 of 0.8, 3.9 and 1.2 degrees C, respectively. Flow microcalorimetry data demonstrated a decrease in the ability of uraemic albumin to bind octanoate, phenol red, salicylic acid, warfarin and diazepam. Purification of uraemic plasma at pH 5.08 completely restored the binding affinity of albumin for all the marker ligands. CONCLUSIONS: Highly efficient activated carbons, with clinically feasible acidification of plasma, can remove strongly albumin-bound uraemic toxins. Investigation of the melting curve of the isolated albumin is a new biophysical way to monitor both its molecular condition and the extent of removal of protein-bound toxins by dialysis. The melting curve provides new qualitative and quantitative information about albumin in an analogous way to an electrocardiogram and the heart.

Albumin, bilirubin, and activated carbon: new edges of an old triangle.

The problem of interaction of human serum albumin (HSA), unconjugated bilirubin (UB) and high porosity activated HSGD carbons is investigated in this study. The decrease of UB to HSA molecular ratio by more than 300 times was demonstrated while the batch experiments in HSA-UB admixtures after contact with HSGD. HSGD carbons express extremely high activity for the removal of UB from HSA containing solutions (more than 100 mg of UB per 1 g of activated carbon). Ex-tempore albumin-coating of carbon surface decreases adsorbent capacity by bilirubin on 21%. At the same time ex-tempore albumin-coating of HSGD carbon surface as well as blood citratization prevent platelet and leukocytes loss and clotting inside of the column. Pharmacopoeia solution of HSA containing acetyl-tryptophan or octanoate used for albumin-coating of HSGD adsorbents, becomes ligand-free and rather more active in complexing with protein-bound substances. Combination of albumin-coated HSGD carbon as haemosorbent with HSA ligand-free solution as a transfusion media seems a new prospective modality of the extracorporeal removal of protein-bound toxins.

Effect of protein-bound uraemic toxins on the thermodynamic characteristics of human albumin.

The ability of albumin to bind drugs and other lipophilic organic acids is decreased in chronic renal failure by the accumulation of albumin-bound uraemic toxins such as hippuric acid, indoxyl sulphate and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF). This furan acid is the most highly bound and is not removed by haemodialysis. The inhibitory effects of these three uraemic toxins on the interaction of three marker ligands sodium octanoate (for medium chain fatty acids), salicylic acid and phenol red (bilirubin site/site I) with albumin have been investigated by differential scanning microcalorimetry and flow microcalorimetry. CMPF was the most potent inhibitor and its binding site coincided with that of bilirubin (site I). Indoxyl sulphate binds to the site for medium-chain fatty acids and tryptophan (site II) and hippuric acid, the weakest inhibitor, inhibited binding to the salicylic acid site.