Wu-Wong J R, Chiou W J, Hoffman D J, Winn M, von Geldern T W, Opgenorth T J
Pharmaceutical Products Division, Abbott Laboratories, Abbott Park, IL 60064, USA.
Life Sci. 1996;58(21):1839-47. doi: 10.1016/0024-3205(96)00168-3.
Endothelins (ET) are 21-amino acid peptides that bind to membrane receptors to initiate a wide range of pathophysiological effects. PD-156707, L-749329, Ro-470203, and A-127722 are potent non-peptide ET receptor antagonists developed recently. When tested in human and rat plasma, both ET-1 and -3 and the four aforementioned antagonists exhibited a high degree (> 98%) of plasma protein binding. When ET-1 binding to the receptors was examined, 5% (v/v) of human plasma inhibited ET-1 binding to both ETA and ETB receptors by 80 - 90%. Similarly, 5% (w/v) of human serum albumin inhibited ET-1 binding by 82%, suggesting that the major protein component in plasma which interfered with ET-1 binding to the receptors was serum albumin. Competition studies show that, in the absence of human serum albumin, the IC50 values of PD-156707, L-749329, Ro-47-0203, and A-127722 were 0.37, 0.29, 5.7, and 0.22 nM, respectively. Addition of increasing doses of human serum albumin incrementally decreased the potency of the antagonists; in the presence of 5% of human serum albumin, the IC50 values increased to 62.8, 50.2, 122.7, and 6.72 nM for PD-156707, L-749329, Ro-47-0203, and A-127722, respectively. In conclusion, ET and ET receptor antagonists exhibit a high degree of binding to plasma proteins, especially serum albumin. Consequently, serum albumin inhibits ET binding to its receptors, and also decreases the potency of ET receptor antagonists. Our findings may explain the discrepancy observed for ET receptor antagonists between in vitro and in vivo potencies.
内皮素（ET）是一种由21个氨基酸组成的肽，它与膜受体结合，引发多种病理生理效应。PD - 156707、L - 749329、Ro - 470203和A - 127722是最近研发出的强效非肽类ET受体拮抗剂。在人和大鼠血浆中进行检测时，ET - 1、ET - 3以及上述四种拮抗剂均表现出高度（> 98%）的血浆蛋白结合率。检测ET - 1与受体的结合情况时，5%（v/v）的人血浆可使ET - 1与ETA和ETB受体的结合分别受到80 - 90%的抑制。同样，5%（w/v）的人血清白蛋白可使ET - 1的结合受到82%的抑制，这表明血浆中干扰ET - 1与受体结合的主要蛋白质成分是血清白蛋白。竞争研究表明，在不存在人血清白蛋白的情况下，PD - 156707、L - 749329、Ro - 47 - 0203和A - 127722的IC50值分别为0.37、0.29、5.7和0.22 nM。添加剂量不断增加的人血清白蛋白会逐渐降低拮抗剂的效力；在存在5%人血清白蛋白的情况下，PD - 156707、L - 749329、Ro - 47 - 0203和A - 127722的IC50值分别增至62.8、50.2、122.7和6.72 nM。总之，ET和ET受体拮抗剂与血浆蛋白，尤其是血清白蛋白，表现出高度结合。因此，血清白蛋白会抑制ET与其受体的结合，同时也会降低ET受体拮抗剂的效力。我们的研究结果或许可以解释在ET受体拮抗剂的体外和体内效力之间所观察到的差异。
