Activity of pancreatic endopeptidases towards luteinizing hormone-releasing hormones

LHRH and its analogues have low oral bioavailability: this is in part due t o their degradation by peptidases present in the intestinal lumen. To deter mine the appropriate inhibitors: to co-administer with LHRH oral formulatio ns. the peptidases involved in their digestion have to be identified. Human (hLHRH) and salmon (sLHRH) LHRH analogues contain a number of potential cl eavage sites for the lumenal pancreatic secreted serine endopeptidases: chy motrypsin, trypsin and elastase. The rats of LHRH degradation by equimolar concentrations of chymotrypsin. trypsin and elastase were examined separate ly in vitro. at pH 8.0. 15 degreesC. At a molar ratio of 1:1000 (enzyme:LHR H). 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), resp ectively. whereas in the presence of elastase both LHRH analogues were slow ly hydrolysed with half-lives of 90 +/- 15 and 114 +/- 21 min (mean +/- S.D . n = 3), respectively. Trypsin had no activity towards either LHRH analogu es after 2 h incubation. The degradation of the LHRH analogues by elastase is likely to be a property of the chymotrypsin impurity. It iu concluded th at protection of the LHRH analogues from alpha -chymotrypsin is a requireme nt For the development of oral absorbable product. (C) 2001 Elsevier Scienc e B.V. All rights reserved.