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.