Roman S, Gulyassy P F, Depner T A
Am J Kidney Dis. 1984 Sep;4(2):153-61. doi: 10.1016/s0272-6386(84)80064-5.
We previously reported that an extract of uremic plasma reduces binding of phenytoin and tryptophan by normal plasma and plasma albumin. This effect appears to reproduce the impaired binding of many drugs and several endogenous metabolites by uremic plasma. In the present study we further characterized the properties of extracts from uremic sera and body fluids using binding of salicylate as a model. Salicylate was chosen because it binds to both of the main albumin binding loci for aromatic, acidic drugs. Using a computer-assisted, least-squares, curve-fitting program, LIGAND, we found that the most satisfactory model for salicylate binding to 1:10 diluted normal plasma was a binding number (n) of 2 mol of salicylate per mole of albumin with an association constant (k) of 2.85 X 10(4) L/mol, an additional binding of 0.5 mol to other sites on albumin or to other proteins, and nonspecific binding of 21%. Addition of uremic pleural fluid extract to diluted normal plasma produced a monotonic decline in k to 0.17 X 10(4) L/mol with no change in n except possibly at the highest dose of uremic inhibitor. This pattern of competitive inhibition indicates presence of unknown ligands in the uremic extract that compete at both binding loci. More efficient extraction methods might also yield additional ligand(s) that inhibit through a noncompetitive mechanism.
我们先前报道过，尿毒症血浆提取物会降低苯妥英和色氨酸与正常血浆及血浆白蛋白的结合。这种效应似乎重现了尿毒症血浆对许多药物和几种内源性代谢物结合的损害。在本研究中，我们以水杨酸盐的结合为模型，进一步表征了尿毒症血清和体液提取物的特性。选择水杨酸盐是因为它能与芳香族、酸性药物的两个主要白蛋白结合位点结合。使用计算机辅助的最小二乘曲线拟合程序LIGAND，我们发现，水杨酸盐与1:10稀释的正常血浆结合的最满意模型是每摩尔白蛋白结合2摩尔水杨酸盐的结合数（n），缔合常数（k）为2.85×10⁴L/mol，在白蛋白或其他蛋白质的其他位点上额外结合0.5摩尔，非特异性结合为21%。向稀释的正常血浆中添加尿毒症胸水提取物会使k单调下降至0.17×10⁴L/mol，n没有变化，除非在最高剂量的尿毒症抑制剂时可能有变化。这种竞争性抑制模式表明尿毒症提取物中存在未知配体，它们在两个结合位点上竞争。更有效的提取方法也可能产生通过非竞争性机制抑制的其他配体。
