ENZYMATIC CLEAVAGE OF THYMOPOIETIN OLIGOPEPTIDES BY PANCREATIC AND INTESTINAL BRUSH-BORDER ENZYMES

The intestinal enzymatic degradation of the immunomodulating peptides thymotrinan (TP3), thymocartin (TP4), and thymopentin (TP5), three oli gopeptides derived from the naturally occurring thymus hormone thymopo ietin, was investigated to evaluate their potential for peroral drug d elivery. In the presence of brush-border membrane vesicles, crude panc reas extract and everted rings from duodenum, jejunum, ileum, and colo n, all peptides were shown to be degraded both by pancreatic enzymes a nd brush-border aminopeptidases. Degradation clearances (Cl-deg) of TP 3, TP4, and TP5 were calculated for a quantitative comparison of pepti de stability. In the presence of crude pancreas extract, there was a r apid degradation of TP5 (Cl-deg 17.9 ml/min) in comparison with TP3 an d TP4 (Cl-deg 0.95 and 0.56 ml/min, respectively, at 0.2 mM peptide co ncentration) caused by the cleavage of the C-terminal tyrosine by carb oxypeptidase A, whereas TP3 and TP4 underwent hydrolysis by aminopepti dase N. In the presence of brush-border membrane vesicles, the degrada tion clearances were 3.9, 3.1, and 2.4 ml/min at 0.2 mM concentrations of TP4, TP5, and TP3, respectively. The clearance of all peptides was lowered with increasing peptide concentrations, indicating saturable degradation processes. The degradation of the thymopoietin oligopeptid es in the presence of brush-border membrane enzymes was exclusively ca talyzed by aminopeptidase N. The degradation of all peptides was highl y dependent on the intestinal segment, with the lowest degradation cle arance observed in the colon. Copyright (C) 1996 Elsevier Science Inc.