Luessen H L, Verhoef J C, Borchard G, Lehr C M, de Boer A G, Junginger H E
Leiden/Amsterdam Center for Drug Research, Leiden University, Division of Pharmaceutical Technology, The Netherlands.
Pharm Res. 1995 Sep;12(9):1293-8. doi: 10.1023/a:1016213405081.
The evaluation of the inhibitory action of two mucoadhesive poly(acrylates), polycarbophil and carbomer, registered by the Food and Drug Administration (FDA), on the intestinal proteolytic enzyme trypsin.
The effect of the polymers on trypsin activity by measuring the degradation of a trypsin specific substrate. Binding of Ca2+ ions and proteins (125I-BSA) to the poly(acrylates). The influence of the polymers on the secondary trypsin structure by circular dichroism.
Trypsin inhibition was found to be time-dependent upon addition of Ca2+ in the degradation experiment. Only when Ca2+ was added within 10 min after trypsin incubation, recovery of the enzyme could be observed. Both polymers showed a strong Ca2+ binding ability. Carbomer, which had a higher inhibitory effect on trypsin activity, also revealed a higher Ca2+ binding affinity than polycarbophil. The amount of Ca2+ depleted out of the trypsin structure and the reduction of enzyme activity were comparable. Immobilization of trypsin by binding to the polymers could not be observed at pH 6.7. Circular dichroism studies suggested that, under depletion of Ca2+ from trypsin, the secondary structure changed its conformation, followed by an increased autodegradation of the enzyme.
The poly(acrylates) investigated may have potential to protect peptides from tryptic degradation and may be used to master the peroral delivery of peptide drugs.
评估两种已获美国食品药品监督管理局（FDA）注册的黏膜黏附性聚丙烯酸酯类聚合物——聚卡波非和卡波姆对肠道蛋白水解酶胰蛋白酶的抑制作用。
通过测量胰蛋白酶特异性底物的降解来研究聚合物对胰蛋白酶活性的影响。研究钙离子和蛋白质（125I-牛血清白蛋白）与聚丙烯酸酯类聚合物的结合情况。利用圆二色性研究聚合物对胰蛋白酶二级结构的影响。
在降解实验中，发现胰蛋白酶抑制作用具有时间依赖性，且依赖于钙离子的添加。只有在胰蛋白酶孵育后10分钟内添加钙离子，才能观察到酶活性的恢复。两种聚合物均表现出较强的钙离子结合能力。对胰蛋白酶活性具有较高抑制作用的卡波姆，其钙离子结合亲和力也高于聚卡波非。从胰蛋白酶结构中耗尽的钙离子量与酶活性的降低程度相当。在pH 6.7时，未观察到胰蛋白酶通过与聚合物结合而被固定化。圆二色性研究表明，在胰蛋白酶的钙离子耗尽时，其二级结构会改变构象，随后酶的自降解增加。
所研究的聚丙烯酸酯类聚合物可能具有保护肽免受胰蛋白酶降解的潜力，可用于控制肽类药物的口服递送。
