Xenopsin-related peptide(s) are formed from xenopsin precursor by leukocyte protease(s) and cathepsin D

Adsorption of (Phe-h5)/(Phe-d5)-substituted peptides from neurotensin family on the nanostructured surfaces of Ag and Cu: SERS studies

This work describes an application of Raman (RS) and surface-enhanced Raman scattering (SERS) to characterize the selective adsorption of two peptides belonging to the neurotensin family peptides, such as kinetensin (KN) and xenopsin-related peptide 2 (XP-2) that are known to stimulate the growth of human tumors. To perform a reliable analysis of SERS spectra, the L-Phe residue (at position 8 or 1 in the amino acid sequence of these peptides) was replaced with L-Phe-d₅ (five protons of L-phenylalanine ring substituted by deuterium). Native and (Phe-d₅)-isotopically labeled peptides were deposited on electrochemically nanostructured surfaces of Ag (AgORC) and Cu (CuORC) from an aqueous solution (H₂O). To determine the share of amide bonds in the interaction with the metallic substrate, SERS spectra of peptides adsorbed on AgORC from heavy water (D₂O) were measured. Also, to determine the effect of the C-end on the SERS spectrum, measurements were made for the KN analog in which the C-terminal L-leucine was removed ([desLeu⁹]KN). Based on the analyses of the spectral profiles, in the spectral range of 600-1650 cm^-1, specific conclusions have been drawn regarding specific aromatic ring···metal interactions and changes in the interaction during substrate change.

Histamine releasing peptide (HRP) has proinflammatory effects and is present at sites of inflammation

Albumin, the most abundant plasma protein, readily enters sites of inflammation during the period of increased vascular permeability. There it encounters proteases released from mast cells and invading leukocytes which earlier work has shown can act on albumin to liberate the peptide, histamine releasing peptide (HRP), first identified and named by its ability to stimulate histamine release from isolated mast cells. In this report we show that HRP releases histamine from cutaneous mast cells in vivo resulting in increased vascular permeability and persistent edema while in vitro, HRP promotes chemotaxis of leukocytes and enhances macrophage phagocytosis. Moreover, we show that the level of HRP is increased with the induction of an acute cutaneous inflammatory response in rats, that HRP is present at sites of acute and chronic inflammation in humans and that HRP is rapidly degraded by proteases thereby limiting its action to the area of its generation. We suggest that HRP is a pro-inflammatory peptide that helps amplify and perpetuate the inflammatory response. Inhibitors of inflammatory proteases or antagonists that block the action of peptides like HRP may, therefore, be useful in breaking the cycle of inflammation.

Pro-xenopsin(s) in vesicles of mammalian brain, liver, stomach and intestine is apparently released into blood and cerebral spinal fluid

Mammalian pro-xenopsins (proXP), proteins (such as alpha-coatomer) that yield XP-related peptides when digested by pepsin-related proteases, are ubiquitously distributed in rats, with highest concentrations in liver and gastrointestinal tissues. Here, the cellular and subcellular distributions of canine and rat proXP were determined in brain, liver, stomach and intestine. Elutriation and percoll density centrifugation of collagenase-dispersed cells demonstrated that proXP was primarily associated with hepatocytes in liver, chief and parietal cells in stomach and endocrine/exocrine cells in intestine. When fragmented cells were subjected to differential centrifugation, congruent with85% of proXP was associated with particulate fractions and only congruent with15% was cytosolic. Sucrose-gradient centrifugation of crude mitochondrial preparations (P2 pellets) for liver, stomach and intestine demonstrated that proXP was localized to vesicles (density, congruent with1.19; size, 80-400 micrometer), which contained material of variable electron density. In isotonic homogenates of brain, proXP migrated primarily with synaptosomes (density, congruent with1. 15) which contained vesicles (size, 50-100 micrometer). During HPLC-sizing and ion exchange chromatography, proXP gave at least three components, the major one being an anionic 140-kDa protein. ProXP-like activity was found in human and rat blood, human cerebral spinal fluid and in contents of the gastrointestinal lumen. These results are consistent with the idea that these vesicle-associated protein(s) could be released during endocrine and/or exocrine secretion and serve as precursors to XP-related peptides.

Opioid peptides derived from hemoglobin: hemorphins

Investigation of hemoglobin peptic hydrolysate has revealed the presence of biologically active peptides with affinity for opioid receptors. Two peptides, VV-hemorphin-7 and LVV-hemorphin-7, were resolved by a combination of size exclusion and reversed phase HPLC. A new spectroscopic method based on the second order derivative spectra analysis of aromatic amino acids has been developed. This method allows qualitative and quantitative evaluation of hemorphins generated by peptic hemoglobin hydrolysis. Using this method, a kinetic study of hemorphins appearance has been undertaken. In this paper, we also evidenced the generation of VV-hemorphin-7 from globin by peritoneal macrophages. In regard to this result, the putative physiological role of hemorphins is discussed.

Neokyotorphin formation and quantitative evolution following human hemoglobin hydrolysis with cathepsin D

In vitro human hemoglobin hydrolysis by cathepsin D was investigated. The quantitative evolution of neokyotorphin following the hydrolysis was determined by high-performance liquid chromatography coupled with a photodiode array detector. Spectral comparisons allowed us to identify neokyotorphin in the hydrolysates all along the hydrolysis. Second order derivative spectrometry was used in order to verify the presence of tyrosine in the peptide. This provided informations about the mechanism of cathepsin D activity towards hemoglobin. Moreover it confirmed that hemoglobin could appear as a precursor of some bioactive peptides following proteolytic degradation.

Hemorphin peptides are released from hemoglobin by cathepsin D. radioimmunoassay against the C-part of V-V-hemorphin-7: an alternative assay for the cathepsin D activity

In order to investigate the putative physiological role of the in vivo release of hemorphins from hemoglobin in tissues, an immunological approach was developed. Specific and sensitive antiserum were raised against the C-part of the V-V-hemorphin-7. The antisera recognized to the same extent the related hemorphins V-V-hemorphin-7 and L-V-V-hemorphin-7. The validity of our immunological approach was analyzed by studying the in vitro release of hemorphin from hemoglobin by cathepsin D and compared to the pepsin hydrolysis. These two enzymes led to the release of these same products suggesting that cathepsin D acted as an accurate pepsin-like enzyme. Moreover, considering the poor sensitivity of the available methods of detection for the in vitro Cathepsin D activity, our specific and sensitive V-V-hemorphin-7 radioimmunoassay seems to be a useful alternative assay for this enzymatic activity.

Generation of VV-hemorphin-7 from globin by peritoneal macrophages

Bovine globin has been incubated with mice peritoneal macrophages in order to study its hydrolysis by lysosomal enzymes, among which chiefly cathepsin D. Analysis of resulting peptides, by reversed-phase high-performance liquid chromatography (RP-HPLC), showed the release of a bioactive peptide, VV-hemorphin-7. When a carboxyl proteinase inhibitor such as pepstatin A was added, no hemorphin was generated. Our results clearly demonstrated that VV-hemorphin-7 generation was principally due to cathepsin D. This study allowed us to hypothesize a possible pathway for in vivo hemorphins appearance from globin catabolism by macrophages.

Purification and characterization of enkephalin-related peptides released by in vitro peptic digestion of bovine plasma proteins

In vitro pepsin treatment of plasma proteins generates biologically active peptides such as enkephalin-related peptides. These peptides were characterized using chromatographic techniques along with a radioimmunoassay procedure involving the use of Leu-enkephalin and Met-enkephalin antisera. Serum albumin is the only existing source of Met-enkephalin-immunoreactive peptides. One of these peptides consists of nine residues with the sequence NH2-Glu-Lys-Leu-Gly-Glu-Tyr-Gly-Phe-Gln; a second immunoreactive peptide might be the hexapeptide NH2-Gly-Glu-Tyr-Gly-Phe-Gln, which has been already identified in a rat serum albumin hydrolysate. Our results indicate that immunoglobulins constitute the main source of Leu-enkephalin-immunoreactive peptides. Immunoreactive NH2-Tyr-Phe-Leu was isolated from pepsin-treated bovine immunoglobulins. Binding experiments and cyclic nucleotide measurements suggested that this peptide was an enkephalin-related peptide. Similar experiments could be carried out to identify the proteins that contain enkephalin-like peptide sequences with the view to investigating the various biological processes occurring in enzymatically treated proteins.

Generation of xenopsin-related peptides from tissue precursors by media conditioned by endotoxin-stimulated rat peritoneal macrophages

Incubation of media conditioned by endotoxin-stimulated rat peritoneal macrophages generates immunoreactive xenopsin (iXP) when incubated with acid extracts of various tissues of the rat. The generation of iXP, as measured by specific radioimmunoassay and confirmed by HPLC analysis, increased as the length of the incubation period increased and was inhibited by pepstatin, prior boiling of the conditioned media, or by omitting either the tissue extract or the conditioned media. The pH optimum for the generation of iXP was 3.0. The generated iXP showed biological activity in that stimulated histamine secretion from isolated rat mast cells and this secretory response was prevented by metabolically poisoning the cells. In addition, the generated iXP stimulated contraction of the isolated guinea pig ileum. In this regard, it was similar to neurotensin (NT). Tissue precursor levels for iXP, as measured by this system of generation, were highest in kidney, liver, and skin and lowest in skeletal muscle and plasma. These results suggest to us that during the inflammatory response, the NT-related peptide, xenopsin, can be generated from tissue precursor(s) by enzymes secreted by invading macrophages. The generated XP may then affect the participating cells of inflammation.