A fluorimetric assay for aminopeptidase W

Enhancement of oral drug absorption—Effect of lipid conjugation on the enzymatic stability and intestinal permeability of l-Glu-l-Trp-NH2

The dipeptide l-Glu-l-Trp-OH (IM862) is currently under development for the treatment of certain cancers and immuno-deficiency disorders. However, due to its highly hydrophilic character, IM862 demonstrates low permeability across biological membranes, including the gastro-intestinal track, which makes it not orally available. In this study, the effect of lipid conjugation on the stability and intestinal permeability of the IM862 amide derivative l-Glu-l-Trp-NH(2) was investigated using enzymatic extracts and monolayers of Caco-2 cells, respectively. A series of eleven novel lipopeptide analogues of l-Glu-l-Trp-NH(2) was synthesized using tert-butyloxycarbonyl or 9-fluorenylmethoxycarbonyl solid-phase peptide synthesis. In vitro assays demonstrated an improved stability to proteolytic enzymes and increased intestinal permeability for several conjugates, thereby supporting the hypothesis that lipidation may provide a means to enable the oral administration of IM862.

Comparison of distribution of brush-border exo- and endopeptidases in rat and rabbit intestine

The distribution of brush-border endopeptidase-2, aminopeptidase W, carboxypeptidase P, and aminopeptidase P along the rat and rabbit intestine was examined. In both species, aminopeptidases P and W increased distally and reached the highest in the ileum; their activities in the ileo-caecal junction were the lowest. Endopeptidase-2 had a uniform intestinal distribution in both species with the highest activity in the ileum and little activity in the ileo-caecal junction or caecum. With a distribution similar to that of endopeptidase-2, carboxypeptidase P also had high activity in the ileum in rats and rabbits.

Distribution of brush-border membrane peptidases along the rat intestine

The longitudinal distribution of brush-border endopeptidase-24.11, endopeptidase-2, aminopeptidase W, angiotensin-converting enzyme (ACE), dipeptidyl peptidase IV (DPP IV), carboxypeptidase P, and aminopeptidase P in the rat intestine was determined. The jejunum has the highest activities of endopeptidase-24.11 and ACE while the ileum has the highest activities of aminopeptidase W and carboxypeptidase P, and the jejunoileal junction has the highest activity of aminopeptidase P. The jejunum and ileum have similar activities of DPP IV. The profiles of differential hydrolysis of neurotensin and acetylneurotensin (8-13) along the intestine agree with distribution of endopeptidase-24.11 and ACE, suggesting that amino acid sequences of peptides and the substrate specificity of enzymes will determine site-dependent hydrolysis. There is substantial similarity in the intestinal distribution of peptidases in the human, rat, and rabbit.

Membrane peptidases in the pig choroid plexus and on other cell surfaces in contact with the cerebrospinal fluid

A comprehensive survey of 11 peptidases, all of which are markers for renal microvillar membranes, has been made in membrane fractions prepared from pig choroid plexus. Two fractionation schemes were explored, both depending on a MgCl2-precipitation step, the preferred one having advantages in speed and yield of the activities. The specific activities of the peptidases in the choroid-plexus membranes were, with the exception of carboxypeptidase M, lower than in renal microvillar membranes: those of aminopeptidase N, peptidyl dipeptidase A ('angiotensin-converting enzyme') and gamma-glutamyltransferase were 3-5-fold lower, those of aminopeptidase A and endopeptidase-24.11 were 12-15 fold lower, and those of dipeptidyl peptidase IV and aminopeptidase W were 50-70-fold lower. Carboxypeptidase M had a similar activity in both membranes. Alkaline phosphatase and (Na+ + K+)-activated ATPase were more active in the choroid-plexus membranes. No activity for microsomal dipeptidase, aminopeptidase P and carboxypeptidase P could be detected. Six of the peptidases and (Na+ + K+)-activated ATPase were also studied by immunoperoxidase histochemistry at light- and electron-microscopic levels. Endopeptidase-24.11 and (Na+ + K+)-activated ATPase were uniquely located on the brush border, and the other two peptidases appeared to be much more abundant on the endothelial lining of microvessels. Dipeptidyl peptidase IV and aminopeptidase W were also detected in microvasculature. Pial membranes associated with the brain and spinal cord also stained positively for endopeptidase-24.11, aminopeptidase N and peptidyl dipeptidase A. The immunohistochemical studies indicated the subcellular fractionation did not discriminate between membranes derived from epithelial cells (i.e. microvilli) and those from endothelial cells. The possible significance of these studies in relation to neuropeptide metabolism and the control of cerebrospinal fluid production is discussed.