Structure of a biologically active neurotensin-related peptide obtained from pepsin-treated albumin(s)

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.

Analysis of spatial and temporal protein expression in the cerebral cortex after ischemia-reperfusion injury

Background and Purpose

Hypoxia, or ischemia, is a common cause of neurological deficits in the elderly. This study elucidated the mechanisms underlying ischemia-induced brain injury that results in neurological sequelae.

Methods

Cerebral ischemia was induced in male Sprague-Dawley rats by transient ligation of the left carotid artery followed by 60 min of hypoxia. A two-dimensional differential proteome analysis was performed using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry to compare changes in protein expression on the lesioned side of the cortex relative to that on the contralateral side at 0, 6, and 24 h after ischemia.

Results

The expressions of the following five proteins were up-regulated in the ipsilateral cortex at 24 h after ischemia-reperfusion injury compared to the contralateral (i.e., control) side: aconitase 2, neurotensin-related peptide, hypothetical protein XP-212759, 60-kDa heat-shock protein, and aldolase A. The expression of one protein, dynamin-1, was up-regulated only at the 6-h time point. The level of 78-kDa glucose-regulated protein precursor on the lesioned side of the cerebral cortex was found to be high initially, but then down-regulated by 24 h after the induction of ischemia-reperfusion injury. The expressions of several metabolic enzymes and translational factors were also perturbed soon after brain ischemia.

Conclusions

These findings provide insights into the mechanisms underlying the neurodegenerative events that occur following cerebral ischemia.

Involvement of neurotensin in cancer growth: evidence, mechanisms and development of diagnostic tools

Focusing on the literature of the past 15 years, we evaluate the evidence that neurotensin and neurotensin receptors participate in cancer growth and we describe possible mechanisms. In addition, we review the progress achieved in the use of neurotensin analogs to image tumors in animals and humans. These exciting advances encourage us to pursue further research and stimulate us to consider novel ideas regarding the multiple inputs to cancer growth that neurotensin might influence.

Critical role of mast cells in inflammatory diseases and the effect of acute stress

Mast cells are not only necessary for allergic reactions, but recent findings indicate that they are also involved in a variety of neuroinflammatory diseases, especially those worsened by stress. In these cases, mast cells appear to be activated through their Fc receptors by immunoglobulins other than IgE, as well as by anaphylatoxins, neuropeptides and cytokines to secrete mediators selectively without overt degranulation. These facts can help us better understand a variety of sterile inflammatory conditions, such as multiple sclerosis (MS), migraines, inflammatory arthritis, atopic dermatitis, coronary inflammation, interstitial cystitis and irritable bowel syndrome, in which mast cells are activated without allergic degranulation.

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.

Proteolytic degradation of hemoglobin by endogenous lysosomal proteases gives rise to bioactive peptides: hemorphins

Hemorphin generation by mice peritoneal macrophages has been recently reported, nevertheless no conclusive data exist to localize clearly the macrophage proteolytic activity implicated in their generation. Because lysosomes are believed to be the main site of degradation in the endocytic pathway, we have studied their potential implication in the generation of hemorphins from hemoglobin. When this protein is submitted to purified rat liver lysosomes, an early generation of hemorphin-7-related peptides, detected by a radioimmunoassay, was observed. These peptides seemed to be relatively stable during the first hours of hydrolysis.

Peptides from bovine brain: structure and biological role

Fractionation of bovine brain extracts followed by automatic Edman sequencing of individual components resulted in identification of 107 endogenous peptides formed from functional proteins (haemoglobin, myelin basic protein, cytochrome c oxidase, etc) or unknown precursors. Several of the newly identified brain peptides demonstrate different types of biological activity; some of the substances show considerable overlap with the known biologically active peptides. It is suggested that these peptides should participate in regulation of extracellular and intracellular biochemical processes. A concept of 'tissue-specific peptide pool' is formulated describing a novel system of peptidergic regulation, complementary to the conventional hormonal and neuromodulatory systems. According to that description functional proteins provide their proteolytically derived fragments for maintaining the tissue homeostasis by modulating the availability of peptide receptors to respective 'true' ligands.

Xenin--a review

Xenin, a 25 amino acid peptide, has been identified in human gastric mucosa in the search for a counterpart to the amphibian octapeptide xenopsin. Xenin is structurally related also to the hypothalamic and ileal peptide neurotensin and is, therefore, a member of the xenopsin/neurotensin/xenin peptide family. The biological activities of these peptides are similar: Xenin has been shown to inhibit pentagastrin-stimulated secretion of acid, to induce exocrine pancreatic secretion and to affect small and large intestinal motility. In the gut, xenin interacts with the neurotensin receptor. Radioimmunoassay and chromatography of postprandial plasma in humans indicate the release of xenin into the circulation. The identification of a 35-amino acid precursor peptide of xenin - proxenin, and a review of the Gen-bank revealed that xenin represents the N terminus of a cytosolic coat protein (alpha-COP) from which xenin can be cleaved by aspartic proteinases such as pepsin and cathepsin E. The physiological role of the peptide xenin is not known.

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.

Comitogenic effects of vasoactive intestinal polypeptide on rat hepatocytes

The primary mitogens such as epidermal growth factor and transforming growth factor-alpha are known to stimulate DNA synthesis in primary cultures of adult rat hepatocytes. Vasoactive intestinal polypeptide (VIP) was found to amplify DNA synthesis induced by the primary mitogens and thus acted as a comitogen. The comitogenic effect of VIP was specific for the culture medium, suggesting that minor components in the medium were required for hepatocytes to fully respond to VIP. Glutamic acid is probably one of these minor components, although other components present in the nutrient-rich medium were also necessary for the full comitogenic effect. Other comitogens such as insulin, vasopressin, and angiotensin II interacted additively with low concentrations of VIP. The comitogenic effect of VIP was also found in hepatocytes cultured from regenerating rat liver after a partial hepatectomy. In the regenerating hepatocyte cultures, VIP can act as a mitogen even in the absence of the primary mitogen EGF. VIP mRNA was found in several organs including brain, intestine, and liver, and its expression was slightly induced in liver 24 h after a partial hepatectomy. These results suggest that VIP can act as a hepatic comitogen and may play a role in liver cell proliferation.

Kinetics of appearance of four hemorphins from bovine hemoglobin peptic hydrolysates by HPLC coupled with photodiode array detection

The kinetics of appearance of hemorphins during peptic hydrolysis of bovine hemoglobin was investigated by reverse-phase high-performance liquid chromatography (RP-HPLC) coupled with a photodiode array detector. The degree of hydrolysis (DH) of hemoglobin by pepsin was determined and different defined DH of hydrolysates were obtained. The analysis of these hydrolysates by HPLC coupled with a photodiode array detector allowed us to identify and quantify the hemorphins in every hydrolysate and to determine the quantitative evolution of hemorphins as a function of DH. It indicated that hemoglobin was a direct precursor of LVV-hemorphin-5 and LVV-hemorphin-7. These peptides were demonstrated to be secondary substrates for pepsin to generate VV-hemorphin-5 and VV-hemorphin-7. Moreover, LVV-hemorphin-7 was more stable towards pepsin than LVV-hemorphin-5. The affinity of pepsin towards some peptidic bonds was also demonstrated.

Kinetic of in vitro generation of some hemorphins: early release of LVV-hemorphin-7, precursor of VV-hemorphin-7

Bovine globin has been hydrolysed by pepsin to different degrees of hydrolysis. Analysis of the hydrolysates, by reversed-phase high-performance liquid chromatography (RP-HPLC), shows the release of LVV- and VV-hemorphin-7. LVV-hemorphin-7 was the first generated, at a degree of hydrolysis (DH), as low as 4%. In contrast, VV-hemorphin-7 was produced later. Our study clearly shows that VV-hemorphin-7 is issued directly from LVV-hemorphin-7, since this later completely disappeared during hydrolysis. This work allows us to suggest a possible pathway for in vivo hemorphins appearance.

Processing of the precursors to neurotensin and other bioactive peptides by cathepsin E

Cathepsin E (EC 3.4.23.34), an intracellular aspartic proteinase, was purified from monkey intestine by simple procedures that included affinity chromatography and fast protein liquid chromatography. Cathepsin E was very active at weakly acidic pH in the processing of chemically synthesized precursors such as the precursor to neurotensin/neuromedin, proopiomelanocortin, the precursor to xenopsin, and angiotensinogen. The processing sites were adjacent to a dibasic motif in the former two precursors and at hydrophobic recognition sites in the latter two. The common structural features that specified the processing sites were found in the carboxyl-terminal sequences of the active peptide moieties of these precursors; namely, the sequence Pro-Xaa-X'aa-hydrophobic amino acid was found at positions P4 through P1. Pro at the P4 position is thought to be important for directing the processing sites of the various precursor molecules to the active site of cathepsin E. Although the positions of Xaa and X'aa were occupied by various amino acids, including hydrophobic and aromatic amino acids, some of these had a negative effect, as typically observed when Glu/Arg and Pro were present at the P3 and P2 positions, respectively. Cathepsin D was much less active or was almost inactive in the processing of the precursors to neurotensin and related peptides as a result of the inability of the Pro-directed conformation of the precursor molecules to gain access to the active site of cathepsin D. Thus, the consensus sequence of precursors, Pro-Xaa-X'aa-hydrophobic amino acid, might not only generate the best conformation for cleavage by cathepsin E but might be responsible for the difference in specificities between cathepsins E and D.

VV-hemorphin-7 and LVV-hemorphin-7 released during in vitro peptic hemoglobin hydrolysis are morphinomimetic peptides

Two opioid peptides were generated by in vitro pepsin treatment of bovine hemoglobin. These peptides were identified using a GPI test and purified using HPLC chromatographic techniques. They correspond to fragments 31-40 (LVV-hemorphin-7) and 32-40 (VV-hemorphin-7) of the beta-chain of bovine hemoglobin. Binding experiments strongly confirm that VV-hemorphin-7 and LVV-hemorphin-7 are opioid peptides since they inhibited [3H]naloxone binding to rat brain membranes. Our results indicate that VV-hemorphin-7 and LVV-hemorphin-7 exhibit a lesser potency both in GPI and binding tests. Selectivity and affinity of these purified peptides and synthetic hemorphin-7 for opioid receptors is discussed.

Blockade of mast cell histamine secretion in response to neurotensin by SR 48692, a nonpeptide antagonist of the neurotensin brain receptor

1. Pretreatment of rat isolated mast cells with SR 48692, a nonpeptide antagonist of the neurotensin (NT) receptor, prevented histamine secretion in response to NT. 2. This inhibition was rapid in onset (approximately 1 min) and dependent upon the concentration of SR 48692 (IC50 approximately 1-10 nM). 3. SR 48692 (1-1000 nM) did not inhibit histamine secretion elicited by substance P, bradykinin or compound 48/80, or by anti-IgE stimulation of sensitized mast cells. 4. When SR 48692 was injected intradermally (5 pmol in 50 microliters) into anaesthetized rats, 15 min before the intradermal injection of NT, it reduced the effect of NT on vascular permeability. 5. When injected intravenously, SR 48692 attenuated the effects of NT on haematocrit and blood stasis. 6. These results demonstrate that SR 48692 selectively antagonizes the actions of NT on rat isolated mast cells as well as mast cells in vivo. Given the demonstrated specific interaction of SR 48692 with receptors for NT in brain, our results suggest the presence of specific NT receptors on mast cells.

Isolation and characterization of ovokinin, a bradykinin B1 agonist peptide derived from ovalbumin

A vasorelaxing peptide was purified from a peptic digest of ovalbumin, after three steps of reverse-phase HPLC. The structure of the peptide was Phe-Arg-Ala-Asp-His-Pro-Phe-Leu, which corresponded to residues 358-365 of ovalbumin. The peptide was named ovokinin. Ovokinin showed relaxing activity for a canine mesenteric artery (EC50 = 6.3 microM). The relaxing activity was blocked by the bradykinin B1 antagonist [des-Arg9] [Leu8]bradykinin, but not by the B2 antagonist Hoe 140. Ovokinin binds to B1 receptors (IC50 = 64 microM). Prostaglandin I2 was released from the artery after ovokinin stimulation as a relaxing factor. Thus, ovokinin is a weak bradykinin B1 agonist peptide derived from food proteins.

Stimulation of hepatocyte DNA synthesis by neurotensin

Epidermal growth factor and transforming growth factor alpha stimulated DNA synthesis in primary cultures of adult rat hepatocytes. Neurotensin amplified epidermal growth factor-stimulated or transforming growth factor alpha-stimulated DNA synthesis by three- to eightfold. Neurotensin by itself did not stimulate DNA synthesis. Amplification of DNA synthesis by neurotensin was observed as low as 10(-10) M, and it was increased in a dose-dependent manner with maximal effects at 10(-8) M. These results were obtained when hepatocytes were cultured in Williams' medium E, but not in Leibovitz L-15 medium, suggesting that a minor component(s) in the medium is required for hepatocytes to fully respond to neurotensin. Neurotensin effect on DNA synthesis was observed not only in normal rat hepatocytes but also in partially hepatectomized rat hepatocytes, although its effect was stronger in normal hepatocytes. Amplified DNA synthesis was inhibited by transforming growth factor beta. Secondary mitogens (co-mitogens) such as insulin, vasopressin, or angiotensin II interacted additively with low concentrations of epidermal growth factor as well as with neurotensin. Neurotensin-related peptides such as kinetensin or neuromedin-N, which was released from blood plasma by pepsin digestion, did not have this amplifying effect on DNA synthesis at any concentrations tested. Neurotensin mRNA was found in several organs including brain and intestine, but not liver. These results suggest that neurotensin can be regarded as a new secondary mitogen and that it may be involved in cell proliferation, including regenerating liver as a gastrointestinal hormone and/or a neurotransmitter.

Purification and primary structure of alligator neurotensin

The gastrointestinal neurohormones of reptiles have been poorly characterized structurally. Neurotensin has been purified to apparent homogeneity from an extract of the small intestine of the alligator, Alligator mississipiensis. The primary structure of the peptide (pGlu-Leu-His-Val-Asn-Lys-Ala-Arg-Arg-Pro-Tyr-Ile-Leu) is identical to that of chicken neurotensin. The data provide further evidence for a close phylogenetic relationship between crocodilians and birds.

Stimulated rat mast cells generate histamine-releasing peptide from albumin

Media conditioned by compound 48/80-stimulated rat mast cells generated immunoreactive histamine-releasing peptide (HRP) when incubated at physiological pH with bovine serum albumin and the carboxypeptidase inhibitor, O-phenanthroline. The generation of immunoreactive HRP (IR-HRP) was time (after 3 h the concentration of IR-HRP was 20 nM), temperature, and pH dependent and was prevented by omitting albumin, by using media conditioned by nonstimulated mast cells, or by pretreatment of mast cells with disodium cromoglycate, an inhibitor of mast cell secretion. The amount of IR-HRP generated increased linearly with the number of mast cells stimulated and varied directly with the concentration of conditioned media. After removal of the media from stimulated mast cells, the remaining cell pellet retained its ability to generate IR-HRP for up to 8 h. Stimulation of mast cells by either neurotensin or substance P, or of sensitized cells by anti-IgE serum, also produced conditioned media that generated IR-HRP. The amount of IR-HRP formed by various conditioned media or by stimulated cell pellets was dependent upon the concentration of O-phenanthroline used. Including the chymase inhibitor, chymostatin, prevented the formation of IR-HRP in a dose-dependent manner. HPLC analysis showed four peaks of IR-HRP. The major one coeluted with synthetic HRP. These results indicate that the peptide, HRP, can be generated by stimulated mast cells incubated in the presence of albumin. They suggest that a chymase-like enzyme secreted by the mast cell is able to cleave albumin to yield HRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and biological activity of kinetensin in conscious sheep

Kinetensin is a nonapeptide, originally isolated from pepsin-treated plasma, that shares some sequence homology with the C-terminal end of neurotensin. The present study was designed to determine, by infusing kinetensin to conscious sheep, the pharmacokinetics and a neurotensin-like biological activity (pancreatic polypeptide response) of kinetensin. Kinetensin was rapidly metabolized, approximately 200-fold more rapidly than neurotensin. The majority of the metabolism occurred in the circulation as demonstrated both in vivo and in vitro. The lung and gut cleared kinetensin also. Inhibition of converting enzyme, present in highest concentration in the lung, abolished lung clearance but was without effect on kinetensin metabolism by the gut or in the general circulation. Arterial infusion of kinetensin which achieved high blood kinetensin levels at the pancreas did not increase plasma pancreatic polypeptide. We conclude that the extremely rapid degradation of exogenous kinetensin, together with the lack of biological activity, makes it unlikely that kinetensin plays a role as a circulating regulatory peptide. Nevertheless, since the putative kinetensin substrate circulates at microM concentrations, it is feasible that kinetensin is generated and metabolized at the target organ.

Effects of GTP analogs and metal ions on the binding of neurotensin to porcine brain membranes

Using 125I-labeled neurotensin (NT), porcine brain membranes were found to contain two types of high-affinity receptors, one class (approximately 1/3 of total) with an apparent Kd of 0.12 nM and another with an apparent Kd of 1.4 nM. Nonhydrolyzable analogs of GTP inhibited NT binding in a dose-dependent manner. In the presence of 60 microM guanosine 5'-(3-thio) 5'-(beta, gamma-imino) triphosphate. NT binding was decreased by 35% with an associated decrease in the number of binding sites and little change in the Kd. Cross-linking of 125I-labeled NT to brain membranes using disuccinimidyl suberate was found to specifically label two substances of approximately 120 kDa and approximately 160 kDa, which could represent different binding proteins or complexes. For a series of NT analogs, there was close agreement between the IC50 in the binding assay and the ED50 in a bioassay based on ability to contract the guinea pig ileum. In addition, metal ions inhibited NT binding and the contractile action of NT with the same order of potency (Hg++ > Zn++ > Cu++ > Mn++ > Mg++ > Li++). There was a linear relationship between the standard reduction potential for these ions and the logarithm of the IC50 in the binding assay. The results suggest that porcine brain contains high-affinity, G-protein-linked receptors for NT, the functioning of which depends upon group(s), perhaps sulfhydryl(s), which can interact strongly with certain heavy metal ions.

Formation of histamine-releasing activity from albumin by medium conditioned by endotoxin-stimulated rat peritoneal macrophages

Incubation of bovine serum albumin (BSA), rat serum albumin or rat plasma with medium conditioned by endotoxin stimulated rat peritoneal macrophages produced an activity that released histamine from isolated rat serosal mast cells. The amount of histamine-releasing activity (HRA) produced increased with the length of the incubation period, with the concentration of albumin, with the number of macrophages stimulated, and with the duration of exposure of the macrophages to endotoxin. Moreover, the formation of the HRA showed a dependency on the pH of the incubation medium with an optimum at pH 4.5. Boiling the medium conditioned by stimulated macrophages before its incubation with albumin or including the acid protease inhibitor, pepstatin with the conditioned medium prevented the formation of HRA. The generation of HRA was not inhibited by pretreatment of the macrophages with the inhibitor of protein synthesis, cycloheximide. Media from macrophages not stimulated with endotoxin failed to generate HRA. Histamine release from mast cells in response to the HRA was inhibited by pretreatment of the cells with antimycin A and deoxyglucose or by preincubation in Ca-free Locke's solution containing a calcium chelating agent. When injected intradermally into anesthetized Evan's Blue treated rats, the generated HRA produced a change in vascular permeability that was prevented by the H1 antagonist, diphenhydramine. Treatment of the HRA with carboxypeptidase A reduced its ability to stimulate histamine release from mast cells. Histamine-Releasing Peptide (HRP), a neurotensin-related octapeptide, shown previously by us to be formed by the action of cathepsin D or pepsin on albumin, was identified by radioimmunoassay in acid:acetone extracts of the histamine-releasing activity. It is concluded that the formation of HRA is due to the actions of enzymes released from macrophages acting on albumin. It is suggested that such histamine-releasing activity could be formed during the later stages of the inflammatory response and that HRP is one of the peptides present.

Rapid degradation of neurotensin by stimulated rat mast cells

A RIA towards neurotensin (NT) using C-terminal- and N-terminal-specific antisera was used to study degradation of this tridecapeptide by isolated rat mast cells. Incubation of NT (10 microM) with peritoneal or pleural mast cells resulted in a rapid loss of NT immunoreactivity (iNT), as measured by C-terminal-directed antiserum, with little effect on N-terminal iNT. The rate of the reaction was faster with pleural cells (T1/2, 30 s) than with peritoneal cells (T1/2, 180 s) and was greater than 10-fold slower in the presence of metabolic poisons. The enzyme(s) involved is most likely released from the cells during secretion, as NT was degraded by media conditioned by compound 48/80-stimulated mast cells 40-60 times faster than by media from unstimulated cells. This degradation by conditioned media was concentration dependent, pH dependent, and temperature sensitive. HPLC analyses indicated a near stoichiometric conversion of NT to NT(1-12) (66%) and NT(1-11) (34%) after incubation for 10-30 s with conditioned media. By 30 min only NT(1-11) and NT(1-10) were present. Phenanthroline (1 mM), an inhibitor of carboxypeptidase, prevented the loss of C-terminal iNT and the generation of NT(1-12) and NT(1-11). While NT(1-12) was effective in releasing histamine from mast cells in vitro and increasing vascular permeability in vivo, NT(1-11) was not. These results suggest that carboxypeptidase-like enzyme(s) could modulate the level and form of NT-related peptides in various states involving activation of mast cells.

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.

Albuminamide: a novel peptide amide isolated from bovine serum

During a systemic search for peptides that possess the C-terminal amide structure, a novel heptapeptide with isoleucine amide was isolated from bovine serum by sequential steps of reversed phase HPLC. Microsequence and amino acid analyses revealed the structure: Asp-Thr-His-Lys-Ser-Glu-Ile-NH2. Since this peptide has the identical sequence to N-terminal (1-7) fragment of bovine serum albumin (BSA), we have designated it albuminamide. The final HPLC step yielded 10 micrograms of homogeneous peptide preparation from 1 liter of bovine serum.

Recent developments in the chemistry of gastrointestinal peptides

Work carried out in different laboratories has shown that the peptide pattern of the intestinal tissue is very complex and that some of the peptides are identical to those found in the central nervous system. The best studied of the peptides are of a hormonal nature, but recently evidence has been obtained that others may primarily act as antibiotics. In addition, peptides have been isolated that are fragments of some well-known proteins that have not been viewed as being prohormones. Whether the latter peptides only represent transient degradation products of the proteins or whether, at least some of them, have a physiologically meaningful selective function of their own is not yet clear.

Isolation and structures of xenopsin-related peptides from rat stomach, liver and brain

Using radioimmunoassay for detection, a mammalian counterpart to amphibian xenopsin (XP) was isolated and sequenced from pepsin-treated extracts of three different rat tissues and shown to be H-Phe-His-Pro-Lys-Arg-Pro-Trp-Ile-Leu-OH. This peptide, which shares six of the eight residues in XP, existed primarily in large molecular form(s) in the rat from which it could be liberated by the enzyme, pepsin. The XP-related sequence was differentially distributed through tissues, with concentrations ranging from ca. 80 pmol/g in diaphragm and skeletal muscle to ca. 800 pmol/g in stomach, liver and intestine. Like XP, the mammalian peptide potently crossreacted in a radioreceptor assay for neurotensin. These results prove the existence of radioreceptor-active XP-related sequences in multiple tissues of the rat.

Canine neurotensin, neurotensin6-13 and neuromedin N: primary structures and receptor activity

Canine neurotensin (NT) and neuromedin N (NMN) were isolated from extracts of ileal mucosa using radioimmunoassay for detection. The structures determined were consistent with those predicted by earlier cDNA work. The molar ratio of NT to NMN was ca. 7, suggesting that the NT/NMN precursor, which contains one copy of each peptide, undergoes complex posttranslational processing or that other NT-precursors lacking NMN exist. In addition to NT, small quantities of NT6-13 and NT2-13 were obtained. Native and synthetic preparations of these peptides were indistinguishable in a radioreceptor assay employing rat brain membranes and 125I-labeled NT; NT6-13 was ca. 8-times more potent than NT and NMN was about one-sixth as potent as NT. NT6-13 was also ca. 10 times more potent than NT in inhibiting spontaneous contractile activity in longitudinally-oriented smooth muscle strips of porcine jejunum. Preparations of intestinal N-cells as well as N-cell vesicles also appeared to contain NT2-13 and NT6-13; however, it is not yet clear whether these peptides are utilized physiologically or simply represent metabolites of NT. These results suggest that further work on the processing of NT precursor and on biologic abilities of partial sequences of NT could be fruitful.

Rapid purification and characterization of histatins (histidine-rich polypeptides) from human whole saliva

Three different polypeptides capable of stimulating histamine release from mast cells were isolated from human whole saliva, using heparin-gel chromatography followed by reversed-phase HPLC. The amino acid sequences of these peptides were shown to be identical to those of histatins 1, 3 and 5.

Neurotensin binding sites in porcine jejunum: biochemical characterization and intramural localization

Neurotensin is present in high concentrations in the mammalian gut, especially in enteroendocrine cells of the mucosa. Exogenous neurotensin has been shown to alter ion transport by the mucosa and contractile activity of intestinal smooth muscle. The purpose of this study was to determine the distribution of neurotensin binding sites within the intestinal wall. Initially, biochemical characteristics of [125I]neurotensin binding sites were determined within two preparations of the distal porcine jejunum: (1) the mucosa and submucosa, and (2) the circular and longitudinal muscle with their intramural plexuses. Ligand binding data for the preparation including the mucosa and submucosa indicated that [125I]neurotensin bound specifically to two sites having apparent equilibrium dissociation constants of approximately 0.046 and 0.37 nM. A binding site with a dissociation constant of approximately 0.38 nM was confirmed for the preparation of muscle and associated intramural plexuses. Xenopsin and neurotensin were equipotent to neurotensin in competing for these binding sites; neuromedin N was approximately 40 times less potent in the preparation of mucosa and submucosa. Receptor autoradiography was used to determine the distribution of [125I]neurotensin binding sites within the wall of the jejunum. Autoradiograms of [125I]neurotensin bound to cross sections of the proximal and distal jejunum showed that the highest densities of silver grains were associated with the internal submucosal ganglia, external submucosal plexus and myenteric ganglia. A moderate density of silver grains was associated with the circular muscle. The localization of neurotensin binding sites to submucosal ganglia is consistent with observations that neurotensin effects on active anion secretion by the mucosa are blocked by tetrodotoxin. Immunohistochemical localization of neurotensin in the porcine jejunum demonstrated a limited population of neurotensin immunoreactive cells within the mucosal epithelium. It is possible that neurotensin released from these cells in the mucosa as well as neurotensin-related peptides released from enteric neurons may be the endogenous ligands for the binding sites visualized in this study.

Neurohormonal peptides in the gut of the Atlantic hagfish (Myxine glutinosa) detected using antisera raised against mammalian regulatory peptides

Concentrations of regulatory peptides in an extract of the intestine of the cyclostome, Myxine glutinosa (Atlantic hagfish), were measured by radioimmunoassay using 12 antisera of defined regional specificity that were raised against mammalian gastrointestinal peptides. The hagfish gut contained somatostatin-, cholecystokinin/gastrin-, C-terminal substance P-, and neurokinin A-like immunoreactivity in concentrations that were 10 to 100 times less than the corresponding concentrations in the rat intestine. The hagfish gut also contained glucagon-like immunoreactivity, measured with both C- and N-terminally directed antisera, but the immunoreactivity did not dilute in parallel with the porcine glucagon standard in radio-immunoassay. No immunoreactivity was detected using antisera to calcitonin gene-related peptide, gastrin-releasing peptide, neuromedin U, neurotensin, N-terminal substance P, and vasoactive intestinal polypeptide. The somatostatin-like immunoreactivity in the hagfish gut was resolved by HPLC into components with the retention times of somatostatin-34 and somatostatin-14, previously isolated from the hagfish islet organ (relative abundance 2:1). The retention times of hagfish glucagon and of the multiple molecular forms of the tachykinin-like peptides were appreciably different from the retention times of the corresponding mammalian peptides.

Generation of histamine-releasing activity from serum albumin by medium derived from stimulated neutrophils of rat

1. Medium conditioned by rat neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine (FMLP) has been found to generate mast cell histamine-releasing activity (HRA) when incubated with bovine serum albumin (BSA). 2. Histamine release increased as the concentration of BSA used to generate HRA was increased from 0.25 to 10 mg ml-1, as the concentration of neurotrophil conditioned medium was increased and as the concentration of FMLP used to stimulate the neutrophils was increased. Histamine release was non-cytotoxic as it was inhibited by energy deprivation or by removal of calcium and it was accompanied by degranulation. 3. HRA was detectable after 30 min of incubation with BSA and its generation continued to increase over the 18 h of our measurements. 4. Generation of HRA was dependent upon the presence of medium from stimulated neutrophils and on the presence of BSA, although plasma could substitute for BSA. Likewise, HRA could be generated from gamma-globulin although to a lesser extent than with albumin. 5. Generation was optimum at acid pH and was inhibited by prior boiling of the neutrophil conditioned medium or by the addition of pepstatin. 6. It is suggested that an enzyme(s) released from the neutrophil during stimulation acts on an albumin-like substrate to generate HRA. It is proposed that HRA is peptide in nature and may be generated during an inflammatory response.

Purification and assay of opioid activity of low molecular weight enkephalin-immunoreactive peptides generated by peptic digestion of rat plasma proteins

A low molecular weight Methionine enkephalin-immunoreactive peptide (MEIP) and two Leucine-enkephalin immunoreactive peptides (LEIP) generated by peptic digestion of rat plasma were purified through gel filtration followed by five sequential reverse phase HPLC gradients in different solvent systems. Binding experiments of these peptides to opioid receptors of rat brains were performed. The two LEIPs were able to inhibit binding of [3H]naloxone to opioid receptors in rat brain membranes. No inhibition was found with the MEIP (which represented the only MEIP present in the low molecular weight fraction of pepsin-digested rat plasma). Sequencing revealed that the MEIP is a six residue peptide with the following sequence: Gly-Glu-Tyr-Gly-Phe-Gln. This sequence corresponds to that of residues 422-427 of rat serum albumin.

Neurotensin and prostaglandin interactions in smooth muscle of the guinea pig stomach

Neurotensin, xenopsin and neuromedin N had a biphasic effect (initial small relaxation followed by a sustained contraction) on the motility of longitudinal muscle strips from the guinea pig gastric corpus. Kinetensin was without effect. Tetrodotoxin, adrenaline, histamine, 5-hydroxytryptamine, opioid peptides, angiotensin II and antagonists of acetylcholine, and desensitization of the strips to bradykinin did not modify the action of neurotensin. The contraction phase was inhibited in a concentration-dependent manner by indomethacin and acetylsalicylate, demonstrating that this activity of neurotensin was dependent on prostaglandin synthesis. The preparation responded to exogenous prostaglandins E1, E2, F1 alpha and F2 alpha with concentration-dependent contractions. The relaxation phase was abolished by verapamil and apamin, indicating the presence of inhibitory neurotensin receptors on smooth muscle cells that are linked to ionic channels.

Secretion of neurotensin from isolated perfused porcine ileum

The secretion and molecular nature of immunoreactive neurotensin (NT) was studied following stimulation of an isolated perfused porcine ileal segment with glucose, triglyceride and intra-arterial infusion of gastrin-releasing peptide (GRP). Secreted peptides were separated using gel chromatography and analyzed with 3 sequence-specific radioimmunoassays towards NT. Glucose (5%) and GRP both stimulated NT secretion from the ileal segment whereas pure triglyceride did not. Maximal secretion of NT during glucose perfusion was 0.448 nmol/min and 6.9 nmol/min during GRP infusion (medians, n = 5). GRP infused in doses from 10(-10) to 10(-8) M stimulated NT release in a dose-related manner. Following gel chromatography only the intact peptide and no smaller or larger molecular size immunoreactive components were observed. The study showed that both luminal and humoral stimuli release NT from the isolated pig ileum. Apparently no fragments or other NT-related immunoreactive components were cosecreted with the peptide.

Neurotensin metabolism in the rat: contribution of the kidney

The kidney plays a key role in the metabolism of neurotensin (NT). We have examined the renal mechanisms of NT clearance by measuring plasma NT basally and after 45 min infusion of NT(1-13) in intact rats, anephric rats (no glomerular filtration, no peritubular metabolism) and ureteral ligated rats (reduced filtration). Plasma NT was measured by radioimmunoassay with both C (biologically active end) and N terminal directed antisera. In anephric and ureteral ligated rats, basal plasma NT like immunoreactivity measured with either antisera was increased 3-fold compared with unoperated rats. C terminal concentrations were higher than N indicating that a C terminal variant of NT was present in basal plasma. Infusion of NT(1-13) increased N terminal NT from 36 +/- 3 to 249 +/- 35 pmol/l (p less than 0.01) in unoperated rats with significantly larger increases in the renally compromised groups. This was reflected in the reduced metabolic clearance rates (measured with the N terminal directed antisera) in the anephric (16 +/- 1 ml/kg/min) and ureteral ligated (17 +/- 3 ml/kg/min) rats when compared with the control rats (26 +/- 4 ml/kg/min). The similar reductions in the anephric and ureteral ligated rats suggested that the decrease in N terminal NT metabolism was from the absence of filtration. Infusion of NT did not increase C terminal NT immunoreactivity in intact, anephric and ureteral ligated rats showing that the C terminal end was extremely labile. However when endogenous converting enzyme activity was blocked by captopril administration there was a significant increase in C terminal immunoreactivity suggesting a role for converting enzyme like proteases in the clearance of the biologically active end of NT.(ABSTRACT TRUNCATED AT 250 WORDS)

Precursor forms of neurotensin (NT) in cat: processing with pepsin yields NT-(3-13) and NT-(4-13)

Basic proteins present in 0.1 N HCl extracts of feline CNS and intestine were found to liberate immunoreactive neurotensin (iNT) when treated with hog pepsin. These protein substrates were separated using Sephadex G-25, Sephadex G-75 and reverse-phase HPLC. In a calibrated SDS-polyacrylamide gel electrophoresis system, the major substrate from cat ileum exhibited a molecular weight of ca 16 kDa and minor substrates were observed at 30, 40 and 65 kDa. As shown previously for synthetic NT, pepsin-treatment of feline ileal NT converted it into the fully immunoreactive NT-(4-13) fragment (yield, 95%). When treated with pepsin, the partially purified ileal substrates gave rise to 4 immunoreactive peptides, one of which (ca 15% of total) eluted with the same retention time as NT-(4-13) while the major peptide formed (ca 40% of total) eluted near to the position of NT-(3-13). Both these products reacted equally well with two different antisera towards the C-terminal 5- and 8-residues of NT and were not recognized by an N-terminal antiserum. Experiments using various proteases demonstrated that the NT-related sequence(s) were located internally in each substrate and suggested that they were bounded by double basic residues. Substrate activity in isotonic homogenates of feline spinal cord, brain, adrenal and ileum cosedimented with iNT during equilibrium centrifugation, apparently in association with vesicle and/or synaptosomal particles. These findings indicate that basic proteins, colocalized with NT in vesicle-like particles of CNS, adrenals and ileum, could serve as precursors to this peptide, being liberated by pepsin-related enzyme(s).