Partial purification and characterization of the drug-binding-defect inducer in uremia

The chemical basis of drug-binding defects in uremia was investigated by studying the effects of extraction of uremic sera with an organic solvent (n-butyl chloride). Extraction of uremic sera at acidic pH (3.0) with n-Butyl chloride fully corrected the binding defects for three acidic drugs (nafcillin, sulfamethoxazole, and salicylate), whereas binding of two basic drugs (trimethoprim and quinidine) was unaffected by similar treatment. When added to normal human serum or purified human serum albumin, the organic solvent layer was capable of inducing binding defects similar to those seen in uremia. Further fractionation of the organic solvent layer with purified human serum albumin at physiologic pH (7.4), followed by reacidification and extraction of the acidified albumin layer with the same solvent, gave a homogeneous fraction on thin-layer chromatography. This homogeneous fraction could induce the binding defects observed in uremia when added to normal human sera. This factor(s) is apparently a dialyzable and weakly acidic compound. It is lipid-soluble and tightly bound to albumin at physiologic pH, but extractable at acidic pH. Its molecular weight is approximately 500 or less. These findings strongly support the hypothesis that the drug-binding defect in uremia is due to accumulation of endogenous metabolic products rather than to an intrinsic structural abnormality in serum albumin.