Activity of pancreatic endopeptidases towards luteinizing hormone-releasing hormones.
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.
AgResearch Ruakura, Biologics Group, Private Bag 3123, Hamilton, New Zealand. walkerg@agresearch.cri.nz
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D000284:Administration, Oral; D000818:Animals; D001682:Biological Availability; D002918:Chymotrypsin / Q000494:pharmacology*; D004347:Drug Interactions; D004355:Drug Stability; D019075:Electrophoresis, Capillary; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D006801:Humans; D010196:Pancreatic Elastase / Q000494:pharmacology*; D012474:Salmon; D014357:Trypsin / Q000494:pharmacology*
D007987:Gonadotropin-Releasing Hormone; D002918:Chymotrypsin; D010196:Pancreatic Elastase; D014357:Trypsin