Walker G F, Ledger R, Tucker I G
AgResearch Ruakura, Biologics Group, Private Bag 3123, Hamilton, New Zealand.
Int J Pharm. 2001 Mar 23;216(1-2):77-82. doi: 10.1016/s0378-5173(01)00571-3.
LHRH and its analogues have low oral bioavailability; this is in part due to their degradation by peptidases present in the intestinal lumen. To determine the appropriate inhibitors to co-administer with LHRH oral formulations, the peptidases involved in their digestion have to be identified. Human (hLHRH) and salmon (sLHRH) LHRH analogues contain a number of potential cleavage sites for the lumenal pancreatic secreted serine endopeptidases: chymotrypsin, trypsin and elastase. The rate of LHRH degradation by equimolar concentrations of chymotrypsin, trypsin and elastase were examined separately in vitro, at pH 8.0, 15 degrees C. At a molar ratio of 1:1000 (enzyme:LHRH), both LHRH analogues were rapidly hydrolysed by alpha-chymotrypsin with half-lives of 2.5+/-0.3 and 2.7+/-0.4 min (mean+/-S.D., n=3), respectively, whereas in the presence of elastase both LHRH analogues were slowly hydrolysed with half-lives of 90+/-15 and 114+/-21 min (mean+/-S.D., n=3), respectively. Trypsin had no activity towards either LHRH analogues after 2 h incubation. The degradation of the LHRH analogues by elastase is likely to be a property of the chymotrypsin impurity. It is concluded that protection of the LHRH analogues from alpha-chymotrypsin is a requirement for the development of oral absorbable product.
促性腺激素释放激素（LHRH）及其类似物口服生物利用度低；部分原因是它们被肠腔内存在的肽酶降解。为了确定与LHRH口服制剂联合给药的合适抑制剂，必须识别参与其消化的肽酶。人（hLHRH）和鲑鱼（sLHRH）LHRH类似物含有许多潜在的胰腔分泌丝氨酸内肽酶切割位点：胰凝乳蛋白酶、胰蛋白酶和弹性蛋白酶。在体外pH 8.0、15℃条件下，分别检测了等摩尔浓度的胰凝乳蛋白酶、胰蛋白酶和弹性蛋白酶对LHRH的降解速率。在酶与LHRH摩尔比为1:1000时，两种LHRH类似物均被α-胰凝乳蛋白酶迅速水解，半衰期分别为2.5±0.3分钟和2.7±0.4分钟（平均值±标准差，n = 3），而在弹性蛋白酶存在下，两种LHRH类似物水解缓慢，半衰期分别为90±15分钟和114±21分钟（平均值±标准差，n = 3）。孵育2小时后，胰蛋白酶对两种LHRH类似物均无活性。弹性蛋白酶对LHRH类似物的降解可能是胰凝乳蛋白酶杂质的特性。结论是，保护LHRH类似物免受α-胰凝乳蛋白酶的作用是开发口服可吸收产品的必要条件。
