Reactive oxygen species induced structural alterations of substance P

Substance P (SP(1-11)) was exposed to a continuous flux of superoxide (O2-) or hydroxyl radicals ((.)OH) in a hypoxanthine (HX)/xanthine oxidase (86 mU) system in the presence of 1 mM deferoxamine and 40 mM D-mannitol or 50 muM FeCI(3). 6H(2)O and 50 muM EDTA, respectively. O2- caused fragmentation between the Phe(7) and Phe(8), whereas (.)OH induced cleavage also between the Phe(8) and Gly(9). Reactive oxygen species H(2)O(2) and HCIO did not cause fragmentation, but modification of the amino acid side chains and/or aggregation with altered hydrophobicity in reverse phase high performance liquid chromatography compared to native SP(1-11). Furthermore, exposure of SP(1-11) to phorbol myristate acetate preactivated neutrophils resuited in products similar to those observed upon exposure to superoxide or hydroxyl radicals in a cell-free HX/xanthine oxidase system. This study suggests that, in contrast to rigid proteins, fragmentation is relatively easily induced in a small peptide like SP(1-11), perhaps due to strain on the peptide and t-carbon bonds caused by the movable, random coil configuration acquired by SP(1-11) in an aqueous solution. Oxidative modification might modulate paracrine actions of SP(1-11) at site of inflammation.     

The antagonism of bombesin in the CNS by substance P analogues

The ability of substance P analogues to inhibit the action of bombesin in the CNS was investigated using receptor binding and biological assays. The putative substance P antagonists inhibited binding to central receptors for both substance P and bombesin-like peptides. Spantide, which was the most potent analogue tested, reversed the bombesin induced hypothermia and grooming. Therefore the putative substance P antagonists may also antagonize the actions of bombesin in the CNS     

Bombesin, bombesin analogues, and related peptides: effects on thermoregulation

The synthesis and biological evaluation on thermoregulation of 39 peptides related to bombesin (structural analogues or other naturally occurring peptides) are described. The bioassay system reported measures the ability of peptides injected intracisternally to lower body temperature of cold (4 degrees C) exposed rats. The most potent analogues of bombesin were those in which positions one to five (not included) were altered, indicating that the decapeptide C terminal was sufficient for full potency. Gln at the seventh position and Gly at the 11th position could be replaced by D-Gln and D-Ala (but not D-Pro or D-Phe), respectively, without any change in potency. Methionine at the 14 position could be replaced with its D isomer with retention of 10% biological activity. Any other alteration of the C terminus (deletions or free acid with the exception of the N-methylamide) drastically reduced the biological potency of those peptides. Among other naturally occurring peptides, alytesin was found to have 100% of bombesin potency whereas litorin, neurotensin, xenopsin, substance P, physalaemin, and eledoisin were found to be in the order of 10(4) times less potent. The shortest peptide found to have full biological activity is the octapeptide des-Glp-Gln-Arg-Leu-Gly-Asn[D-Glp7, D-Ala11]-bombesin.     

Distribution and origin of bombesin,substance P and somatostatin in cat spinal cord

Bombesin (BN), substance P-(SP) and somatostatin (SRIF) were measured in individual laminae of the cervical, thoracic and lumbar (L) spinal cord of control cats, and in the L6 segment of cats receiving a spinal hemisection (L2) or deafferentation via dorsal rhizotomy at L6, 7, S1. The interlaminar distribution of BN, SP, and SRIF was remarkably similar. Highest concentrations were found in the superficial dorsal horn, and progressively less was found proceeding ventrally. Some intersegmental variations in peptide concentration within a single lamina were found. Dorsal rhizotomy caused a significant decline in BN, SP and SRIF in lamina I-III, therefore all three peptides appear to be contained in dorsal root ganglion cells. Evidence is presented for the existence of ascending BN and SP projections originating in lamina I-III and VII, for a descending SRIF pathway terminating in lamina VIII, and for an ascending BN path in lamina VIII. Dorsal root afferents to lamina VIII influence levels of BN, SP and SRIF.     

Salivary secretion induced by substance P

Secretion of fluid, ions, and amylase from parotid and submaxillary glands of rat, induced by intravenous injection of substance P (SP), was examined. The action of SP on salivary glands, like physalaemin, resembled that of cholinergic stimulation. While SP-evoked salivary flow from both glands was blocked by atropine, atropine did not modify composition of SP-evoked saliva. The present study suggests that salivary secretion and secretion of ions and amylase evoked by SP are mediated via SP-sensitive cholinergic receptors and specific SP receptors, respectively.     

Responses of the rat cardiovascular system to substance P,neurotensin and bombesin

The carotid arterial blood pressure and heart rate responses to intravenous injections of substance P, neurotensin and bombesin were compared in anaesthetized rats. In rats anaesthetized with urethane neurotensin produced only a fall in blood pressure but in rats anaesthetized with sodium thiobutabarbitone, the fall was preceded by a transient rise in blood pressure. The reason for the different responses to neurotensin with the two anaesthetics was not investigated. The hypotensive effect of neurotensin observed with both anaesthetics was abolished by mepyramine and therefore appeared to be mediated by action on H₁ receptors either of neurotensin directly or of histamine released. On the other hand, catecholamines might be implicated in the pressor response to neurotensin observed in rats anaesthetized with sodium thiobutabarbitone since it was reduced by phentolamine and hexamethonium. Low doses of substance P produced a depressor response which was not inhibited by the antagonists tested. At higher doses marked tachycardia occurred and the depressor response was less and was often followed by a pressor response. The tachycardia was abolished by propranolol but not by cervical cord section or by hexamethonium. Bombesin produced a pressor response which was unaffected by hexamethonium but was reversed to depressor by phentolamine. This depressor response to bombesin was abolished by propranolol. It was concluded that substance P produced a depressor response by action on its own specific receptors and tachycardia by catecholamine release whereas neurotensin and bombesin produced cardiovascular actions which were mediated entirely by amine release.     

Amyloid-beta peptide, substance P, and bombesin bind to the serpin-enzyme complex receptor.

During the formation of an inhibitory complex with neutrophil elastase, alpha 1 antitrypsin (alpha 1 AT) undergoes a structural rearrangement and the resulting alpha 1 AT-elastase complex becomes endowed with chemoattractant activities, mediates an increase in synthesis of alpha 1 AT, and is rapidly cleared from the circulation. In previous studies we have provided evidence that these biological activities involve the recognition of a conformation-specific domain in the alpha 1 AT molecule by a cell surface receptor on human hepatoma HepG2 cells and human monocytes. The receptor has been termed the serpin-enzyme complex (SEC) receptor because it also recognizes complex of serpins antithrombin III, alpha 1 anti-chymotrypsin, and C1 inhibitor with their cognate enzymes. Because a pentapeptide domain of alpha 1 AT (amino acids 370-374, Phe-Val-Phe-Leu-Met) is sufficient for binding to the SEC receptor and the sequence of this domain is remarkably similar to those of substance P, several other tachykinins, bombesin, and the amyloid-beta peptide, we have examined the possibility that these other ligands bind to the SEC receptor. The results indicate that substance P, several other tachykinins, and bombesin compete for binding to, and cross-linking of, the SEC receptor. The SEC receptor is distinct from the substance P receptor by several criteria. There is no substance P receptor mRNA in HepG2 cells; the SEC receptor is present in much higher density on receptor-bearing cells and binds its ligands at lower affinity than the substance P receptor; the SEC receptor is much less restricted in the specificity with which it recognizes ligand; ligands for the SEC receptor including peptide 105Y (based on alpha 1 AT sequence 359-374), alpha 1 AT-protease complexes, and bombesin do not compete for binding of substance P to a stable transfected cell line expressing the substance P receptor. Finally, we show here that the amyloid-beta peptide competes for binding to the SEC receptor but does not bind to the substance P receptor, therein raising the possibility that the SEC receptor is involved in certain biological activities, including the recently described neurotrophic and neurotoxic effects ascribed to the amyloid-beta peptide.     

Effect of bombesin, bradykinin, substance P and CGRP in prostate, bladder body and neck.

Lower urinary tract tissues respond heterogeneously to adrenergic and cholinergic agents. However, the action of bioactive peptides on these tissues has not been extensively studied. The contractile and relaxant effects of nine peptides-bradykinin, cholecystokinin, vasoactive intestinal polypeptide, gastrin, substance P, bombesin, neuropeptide Y, calcitonin gene-related peptide, and motilin-have been compared in the rat bladder body, bladder neck, and left ventral prostate in vitro. All three tissues contracted to bombesin and to bradykinin, although the bladder neck was less sensitive to the contractile effects of bradykinin than the other two tissues. Substance P only contracted the bladder body. Of all the peptides tested, relaxation was only observed to calcitonin gene-related peptide, which relaxed the bladder neck and prostate (phenylephrine-contracted) but not the bladder body (carbamylcholine-contracted). Thus lower urinary tract tissues are responsive to certain bioactive peptides in a nonhomogeneous fashion. These studies raise the possibility that selective modulation of peptide function may be an approach to therapy of urogenital disorders.     

Fluorescence, CD, and NMR studies on spantide, a bombesin and substance P antagonist.

The conformational properties of spantide [(D-Arg, D-Trp, Leu) substance P] have been studied by fluorescence, CD, and nmr techniques. The fluorescence, CD, and nmr parameters in different solvents and in a micellar environment (SDS) are compared with the data collected for bombesin. A preliminary investigation on [D-Pro] spantide is also reported.     

Amidase-like activity of calpain I and calpain II on substance P and its related peptides

Porcine calpains (Ca2+-dependent cysteine proteinases) I and II, which had been purified each to a homogeneous state, were found to hydrolyze specifically carboxyl-terminal amide of substance P and several other biologically active peptidyl amides. This amidase-like activity was demonstrated both by determining released ammonia and by separating products on high-performance liquid chromatography followed by amino acid analysis. The calpain-catalyzed deamidation of substance P occurred exclusively at the carboxyl-terminal amide, leaving the side-chain glutamine intact. Enkepharinamide and MSH-release inhibiting factor were scarcely deamidated. Calpains I and II showed similar specificities for these amide substances and similar profiles of inhibitions by various protease inhibitors, but distinctly different Ca2+ requirements. The specificity constants, kcat/Km, for substance P were found to be three to four orders of magnitude higher than those for the synthetic substrates.     

Covalently cyclized agonist and antagonist analogues of bombesin and related peptides.

During a search for possible cyclization points in shortened, potent bombesin agonists and antagonists, it was found that the joining of amino acid residues in positions 6 and 14 by various means resulted in retention of significant binding affinity for rat pancreatic acini and murine Swiss 3T3 cells. In one series of analogues, Cys residues in these positions were used for bridging via a disulfide bond. (D)-C-Q-W-A-V-G-H-L-C-NH2 retained significant binding affinity for rat pancreatic acini cells and was a full amylase releasing agonist (EC50 187 nM). Potency was markedly increased by substituting D-Ala for Gly (EC50 67 nM compared to 10 nM for its linear counterpart) and was decreased by substituting L-Cys for D-Cys in this analogue (EC50 214 nM), thus strongly suggesting stabilization of peptide folding by the D residues. Elimination of the COOH-terminal amino acid produces competitive antagonists in the linear analogues; however, (D)-C-Q-W-A-V-G-H-C-NH2 was devoid of activity. Likewise, cyclization to position 13 with the 14 amino acids intact to give (D)-C-Q-W-A-V-G-H-C-L-NH2 resulted in an almost inactive peptide. On the other hand, as in the linear series, the reduced peptide bond analogue, (D)-C-Q-W-A-V-(D)-A-H-L-psi (CH2NH)-C-NH2, was a receptor antagonist (IC50 5.7 mM), albeit much weaker than the corresponding linear analogues, but with no residual agonist activity. Direct head-to-tail cyclization was also tried. Both cyclo[(D)-F-Q-W-A-V-G-H-L-L] (EC50 346 nM) and the shorter cyclo [Q-W-A-V-G-H-L-L] (EC50 1236 nM) were full agonists. Elimination of the COOH-terminal residue in cyclo[(D)-p-Cl-F-Q-W-A-V-(D)-A-H-L] produced an agonist (EC50 716 nM) rather than an antagonist. These results provide support for the proposal that both bombesin agonists and antagonists adopt a folded conformation at their receptor(s). Furthermore, the retention of appreciable potencies using several cyclization strategies and chain lengths suggests that further optimization of these structures both in terms of potency and ring size is possible. Since these peptides have increased conformational restriction, they should begin to serve as useful substrates for NMR and molecular modeling studies aimed at comparing the obviously subtle differences between agonist and antagonist structures.     

500 MHz NMR characterization of synthetic bombesin and related peptides in DMSO-d6 by two-dimensional techniques

The proton NMR characterization of bombesin has been carried out at 500 MHz in DMSO-d6 using two-dimensional homo- and 1H-13C hetero-correlated techniques. All resonances in the NMR spectra have been assigned and several coupling constants have been measured. The backbone J alpha CH-NH coupling constants have constant values that vary between 7.8 and 8.2 Hz and indicate an unfolded structure in DMSO-d6. Discrepancies with data recently obtained at 300 MHz [(1987) Eur. J. Biochem. 168, 193-199] are discussed.     

Behavioral effects of 26RFamide and related peptides

A novel 26-amino acid peptide possessing the Arg-Phe-NH(2) motif at its C-terminal extremity has been recently characterized and named 26RFamide (26RFa). The 26RFa precursor encompasses several potential cleavage sites and thus may generate various mature peptides including an N-terminally extended form of 26RFa (termed 43RFa), two fragments of 26RFa (26RFa(1-16) and 26RFa(20-26)), and a 9-amino acid peptide (9RFa) located in tandem in the human 26RFa precursor. In the present study, we have investigated the central effects of 26RFa and related peptides on food intake and locomotor activity in mice. We observed that i.c.v. injection of 26RFa, 43RFa, 26RFa(20-26) and 9RFa stimulated food consumption while 26RFa(1-16) and 26RFa(8-16) had no effect. A dose-dependent stimulation of locomotor activity was observed after i.c.v. administration of 26RFa, 43RFa and 26RFa(1-16), but not 26RFa(20-26), 26RFa(8-16) or 9RFa. These data indicate that the novel neuropeptides 26RFa and 43RFa act centrally to stimulate feeding and locomotor activities but the domains of the peptide involved in each of these responses are different suggesting that the two behavioral effects may be mediated through distinct receptors.     

Stimulation of canine pancreatic polypeptide, gastrin, and gastric acid secretion by ranatensin, litorin, bombesin nonapeptide and substance P

Four dogs with chronic gastric fistulas were give intravenous bombesin nonapeptide (B9), ranatensin, and litorin by constant infusion for 90 min at 1.2 micrograms x kg-1 on separate days. A dose response study with substance P (1.5, 3.0, 60, 18 and 54 micrograms x kg-1 x h-1) was also carried out and all tests compared to a standard protein meal (10g x kg-1). Plasma gastrin and PP were measured by radioimmunoassay and gastric acid by autobiuret titration. Substance P failed to stimulate gastric acid secretion or release either pancreatic polypeptide (PP) or gastrin. Basal gastrin levels were 8 +/-2 fmol/ml. The peak increment of gastrin released by bombesin was 95 +/- 16, ranatensin 22 +/- 6, litorin 18 +/- 4, and meal 39 +/- 5 fmol/ml. Bombesin caused significantly greater release of gastrin than a meal, litorin or ranatensin (P less than 0.01). Basal gastric secretion was 23 +/- 4 microequiv./min. B9 produced a peak acid secretion of 356 +/- 124 muequiv./min. There was no significant difference between the bombesin-like peptides (P less than 0.01). Basal plasma PP was 38 +/- 12 fmol/ml. B9 produced a peak PP increment of 600 +/- 50, litorin 137 +/- 36, ranatensin 98 +/- 11, and a meal 305 +/- 58 fmol/ml. B9 released significantly more PP than either litorin of ranatensin (P less than 0.01). The different amino acid sequences of the peptides are probably responsible for their potency. The substitution of a penultimate phenylalanine residue in litorin and ranatensin for leucine in bombesin does not prevent PP or gastrin release by bombesin-like peptides. Since bombesin-like peptides are widely distributed in the gastrointestinal tract of man and stimulate both acid and gut hormone secretion, it is possible that they might play a physiological role in the modulation of gastrointestinal function.     

Reproduction in mice: Behavioral changes induced in female mice by mating

Mated C57BL/6J females experienced in food-motivated maze running were found to make more choices and choose more correctly than virgins. The differences correlated with the receipt of spermatozoa and prior pseudopregnancy. Pregnancy, active pseudopregnancy, and male-female social interactions did not appear to be required determinants. The biologic ramifications of mating in mice may extend beyond the fusion of sperm and egg and the induction of hormonal changes that regulate the earliest stages of pregnancy.     

Differential regulation of smooth muscle contraction in rabbit internal anal sphincter by substance P and bombesin.

Substance P and bombesin induce contraction of isolated IAS smooth muscle cells by different intracellular mechanisms. The cells contracted in a dose dependent manner to both peptides. The kinetics of contraction were different. Substance P induced contraction peaked at 30 seconds and declined in a time dependent manner while bombesin induced contraction peaked at 30 seconds and was maintained for up to 8 minutes. The absence of extracellular calcium in the medium (0 calcium and 2 mM EGTA) had no affect on substance P induced contraction while it blocked bombesin induced contraction. Substance P induced contraction was blocked by the calmodulin antagonist W7 (10(-9)M) and was not affected by the PKC antagonist H7 (10(-6)M). Bombesin induced contraction was blocked by the PKC antagonist H7 and was not affected by the calmodulin antagonist W7. Our data indicate that substance P induces a transient contraction utilizing intracellular calcium and a calmodulin dependent pathway, while bombesin induces a sustained contraction utilizing calcium from extracellular sources and a calmodulin independent pathway.     

Cooperative effects of bombesin, substance P and methacholine on the release of intestinal neurotensin in rats.

The secretion of ileal neurotensin (NT) results from events occurring at the apical and basal side of the N-cells. The hypothesis of a functional relationship between cholinergic and peptidergic neurones with the N-cell was investigated in the present study utilizing the isolated vascularly perfused rat ileum. Intraarterial methacholine (MC, 10(-4) M) evoked a prompt and well sustained release of NT in the portal effluent (plateau value at 500% of basal). This effect was dose-dependent over the range of 10(-6) M to 10(-4) M. Bombesin (B) provoked a dose-dependent peak secretion of NT (800% of basal at 10(-7) M) followed by a rapid return to almost basal levels. The B-induced NT release remained unaltered upon 10(-6) M tetrodotoxin (TTX) or 10(-5) M atropine infusion. Substance P (SP) potently stimulated the release of NT. The maximal response, consisting of a sustained secretion, was observed at a concentration of 10(-7) M (350% of basal) while 10(-6) M SP induced a transient release. TTX or atropine did not reduce significantly the SP-induced secretion of NT. Neurokinin A and B did not increase NT concentrations in the portal effluent. B synergistically increased the secretion of NT induced by SP. Atropine or TTX did not modify the effect of combined SP and B infusion. MC potentiated the release of NT induced by B but not that evoked by SP. Combined infusion of SP, B and MC produced the largest output of NT. In conclusion, B, SP and MC are strong stimulants of NT release in rats. In addition, the cooperative effects of these transmitters argue in favor of a complex functional relationship between the intramural nervous network and the intestinal N-cells in rats.     

Inflammatory responses induced by substance P in rat paw.

Substance P (SP) injection in the plantar region of rat hind paw caused a dose related inflammation, which reached a peak within 10 min of injection and declined after 60 min. Low doses (0.25-0.063 mg/kg) of SP-antagonists like (D-Pro2, D-Trp7,9)-SP and (D-Pro2, D-Phe7, D-Trp9)-SP pretreatment significantly inhibited the SP induced paw oedema, while higher doses (0.5-1 mg/kg) showed agonistic effects. Pretreatment with diphenhydramine alone or along with low doses of SP-antagonists was highly significant in blocking this inflammation, the latter combination being more effective than the former. Pretreatment with acute capsaicin produced a synergestic effect on SP induced paw oedema, while pretreatment with chronic capsaicin significantly inhibited this SP induced paw oedema. The results indicate involvement of histamine and possible therapeutic importance of capsaicin in SP mediated inflammatory type of responses.