Involvement of endopeptidase-24.11 in degradation of substance P by glioma cells

Major metabolites of substance P degraded by spinal synaptic membranes antagonize the behavioral response to substance P in rats

Substance P (SP) was degraded by synaptic membranes of rat spinal cord. Cleavage products were separated by reversed phase high performance liquid chromatography and identified by amino acid composition analyses. Major products of SP were phenylalanine, SP(1-4), SP(1-6), SP(1-7), SP(10-11), and SP(8-9). Both the degradation of SP and the accumulation of the major cleavage products were strongly inhibited by a metal chelator, o-phenanthroline, and also by specific inhibitors of endopeptidase-24.11, thiorphan, and phosphoramidon. Thus, endopeptidase-24.11 plays a major role in SP degradation in the rat spinal cord. N-Terminal fragments, SP(1-7) and SP(1-4), detected after incubation with spinal synaptic membranes were examined in vivo for antagonism against the scratching, biting, and licking response induced by intrathecal (IT) injection of SP (3.0 nmol) in rats. When IT coadministered with SP, SP(1-7) and SP(1-4) produced a significant inhibition of behavioral response to SP with ED50 of 135.0 pmol and 6.2 nmol, respectively. These results suggest that the degradation of SP in the spinal cord is not only responsible for inactivation of parent peptide, but may also lead to the formation of N-terminal SP-fragments which are shown to display a novel physiological function.

Enzymes and inhibitors in leu-enkephalin in metabolism in human plasma

The enzymes degrading leucine enkephalin in human plasma and the inhibitors active on these enzymes were studied by kinetic and chromatographic techniques. Data obtained evidence the existence of complex kinetics of leu-enkephalin hydrolysis and of formation of its hydrolysis by-products. These appear to originate from the combined effect of further hydrolysis of the enkephalin's fragments after their release and of competition between the different enzymes present in plasma. Chromatographic separation of plasma proteolysis inhibitors indicates the existence of several pools of substances acting on all three enzyme groups that degrade leu-enkephalin. The partial specificity of these substances induces competition effects: consequently, the actual protection over leu-enkephalin is considerably lower that the total inhibitory activity. That notwithstanding, plasma inhibitors control enkephalin hydrolysis to a relevant extent, while they modify only slightly the ratio of hydrolysis between the different enzymes. This latter parameter--and specifically the large prevalence of aminopeptidases over dipeptidylaminopeptidases and dipeptidylcarboxypeptidases--appears controlled mainly by kinetic factors.

Sample preparation, high-performance liquid chromatographic separation and determination of substance P-related peptides

This review deals with the determination of low levels of substance P and peptide fragments derived from the undecapeptide, i.e. covers the whole amount of so-called substance P-like immunoreactivity (SPLI) in biological samples. First an overview of the most currently used sample pretreatment procedures is given, followed by a description of the most effective high-performance liquid chromatographic (HPLC) separation methods. Special attention is paid to the choice of the appropriate column and the possible pitfalls encountered in separation of fmol amounts of peptide material. Subsequently the most important techniques of detection are discussed. This section primarily focuses on the coupling of HPLC with radioimmunoassay (RIA), which is indispensable for detection of components in the fmol range at present. Finally, some aspects of preparation and chromatographic separation of radiolabelled antigens for use in RIA are discussed.

Hydrolysis of leucine enkephalin and its association to the K562(S) erythroleukaemic cell line

Hydrolysis of Leu-enkephalin and association to cells of the radioactive label carried by this peptide have been studied on the K562(S) erythroleukaemic cell subline. Data obtained indicate that in the presence of these cells Leu-enkephalin is rapidly hydrolyzed and that the peptide's radioactive label is partially associated to the cells. Both phenomena are characterized by distinctly diphasic kinetics, and are oppositely modified by cells' stimulated erythroid differentiation. In the presence of proteolysis inhibitors, hydrolysis of Leu-enkephalin and association to cells of its radioactive label are reduced. These data, indicating that enkephalin hydrolysis is a prerequisite for the association of the radiolabel to cells, are consistent with those obtained with other cell lines of different origins and with human mononucleate cells. The modifications induced by differentiation of cells on hydrolysis, association and membrane conductance can be interpreted as an indication of extensive modifications of the membrane structures responsible for the mechanisms controlling those phenomena.

Effect of differentiation on hydrolysis and association of Leu-enkephalin to K562(S) cells

Hydrolysis of Leu-enkephalin and association to cells of the peptide-radioactive label have been studied on the K562(S) erythroleukemic cell subline. Data obtained indicate that in the presence of these cells, Leu-enkephalin is hydrolyzed, that the peptide's radioactive label is partially associated to cells, and that these phenomena are related. Hydrolysis and association are inversely modified by the cells' differentiation: hydrolysis is increased and association is decreased in differentiated compared with nondifferentiated cells. Moreover, the ratio of hydrolysis by-products is dissimilar between differentiated and nondifferentiated cells as a result of a significant modification of the soluble enzymes' release. The alterations induced by differentiation on all parameters investigated seem to indicate significant changes in the membrane structures responsible for the mechanisms controlling these phenomena.

Effect of stimulation on soluble proteolytic enzymes released by peripheral blood mononuclear cells

The release of soluble peptidases active in the degradation of leucine enkephalin by human peripheral blood mononuclear cells (PBMC), and the effect of stimulation of mononuclear cells on the release of these enzymes are reported. Results obtained indicate that leu-enkephalin is partially degraded in the presence of soluble supernatants prepared from mononuclear cells. In accord with data previously obtained with immunocompetent cell lines, three classes of enzymes appear to be involved in leu-enkephalin hydrolysis: aminopeptidases, dipeptidylaminopeptidases and dipeptidylcarboxypeptidases. Phytohemagglutinin stimulation of mononuclear cells appears to cause a relevant increase of the total activity of the soluble enzymes, as well as a partial rearrangement of the ratio between the different enzyme activities. A similar effect is also evident upon chromatographic separation of the soluble supernatants: the relative activity of the several distinct enzymes--notably aminopeptidases and dipeptidylaminopeptidases--identified after column separation is significantly modified by PBMC stimulation. The effect of stimulation of mononuclear cells on the release of soluble enzymes can be interpreted as an indication of the role of these enzymes--possibly in the regulative process of informational peptides--similar to that described in the case of membrane enzymes.

Soluble enkephalin-degrading enzymes released by lymphomic and erythroleukaemic cell lines

The possible existence of soluble proteolytic enzymes released by cells of lymphomic (U937 and 1301) and erythroleukaemic (K562) lines was studied measuring the hydrolysis of 3H-leucine enkephalin in the presence of cell-free supernatants obtained from these lines. Results indicate that leu-enkephalin is rapidly degraded in the presence of these supernatants, and that enkephalin disappearance is paralleled by the formation of peptides that can be interpreted as its hydrolysis fragments. To characterize the factors involved in leu-enkephalin degradation, cell supernatants were analyzed by ion exchange and by steric exclusion chromatography. Data obtained indicate the presence of three groups of proteins active in leu-enkephalin degradation: aminopeptidases, dypeptidylaminopeptidases and dypeptidylcarboxypeptidases. In all three lines, these enzymes are represented by a considerable number of distinct activities. The sizable number of soluble enzymes identified and the significant total activity observed suggest a possible role in the regulatory degradation of informational peptides, as proposed by several groups for the membrane-bound proteolytic enzymes of immunocompetent cells.

Hydrolysis and association of leucine enkephalin to lymphomic and erythroleukaemic cell lines--III. Soluble enzymes

The possible existence of soluble proteolytic enzymes released by cells of lymphomic (U937 and 1301) and erythroleukaemic (K562) lines was studied measuring the hydrolysis of 3H-leucine enkephalin in the presence of cell-free supernatants. Results obtained indicate that in the presence of these supernatants leu-enkephalin rapidly disappears and that enkephalin disappearance is paralleled by the formation of peptides that can be interpreted as its hydrolysis fragments. Chromatographic analyses of cell supernatants indicate the presence of three groups of proteins active in leu-enkephalin degradation: aminopeptidases, dipeptidylaminopeptidases and dipeptidylcarboxypeptidases. In all three lines, soluble enzymes are represented by a sizeable number (from 13 to 25) of distinct activities. The number of enzymes identified and their considerable total activity suggest a possible role in the regulatory degradation of informational peptides, as proposed by several groups for the membrane-bound proteolytic enzymes of immunocompetent cells.

Expression of cALLa/NEP on gliomas: a possible marker of malignancy

First described on pre-B leukemia cells, the common acute lymphoblastic leukemia antigen (cALLa) is also expressed on glioma cells in vitro. Its identity to neutral endopeptidase (NEP) (E.C.3.24.11) was corroborated by our finding that cALLa positive glioma cells had NEP activity. To study cALLa/NEP distribution on glial tumours in vivo, we examined 76 brain tumour biopsies by immunostaining techniques on frozen tissue sections using anti-cALLa (FAH99) and anti-NEP (135 A 3) monoclonal antibodies. We found that 96% of grade 4 gliomas (25/26) expressed NEP. Whereas only 45% (4/9) of grade 3 or anaplastic astrocytomas did. In low grade gliomas, we found 2 positive tumours out of 21 tested (10%). Double immunostaining procedures revealed that NEP was co-expressed with GFAP. However no NEP could be detected on non-glial brain tumours nor on reactive astrocytes. These results suggest that cALLa/NEP expression could be linked to malignant progression of gliomas.