Dimeric substance P analogue shows a highly potent activity of the in vivo salivary secretion in the rat

Synthesis, characterization and anticonvulsant activity of new azobenzene-containing VV-hemorphin-5 bio photoswitch

A novel analog of VV-hemorphin-5 containing azobenzene moiety has been synthesized and investigated for anticonvulsant activity in relation to its E → Z photophysical properties activated by long wavelength light at 365 nm. The synthesis was achieved by a modified SPPS by Fmoc-dimerization strategy. The electrochemical behavior before and after UV illumination was investigated using different voltammetric modes. The number of electrons transferred, heterogenic rate constant and diffusion coefficient for E- and Z-isomers were also evaluated. Revealing the governing principles involved in signaling and nerve pulse propagation requires the detailed characterization of the electrical properties of cell membranes. For probing the effect of synthesized azo-peptide on the membrane electrical properties, we measured the specific capacitance of lipid bilayers, representing a basic physical model of biomembranes with their simple reproducibility in laboratory conditions at controlled membrane composition and physicochemical parameters of the surrounding aqueous medium. Our results have shown reduced membrane capacitance in the presence of the azo-peptide, thus providing evidences for possible alterations in the dielectric permittivity of the bilayer. The (Val-Val-Tyr-Pro-Trp-Thr-Gln)₂Azo peptide was explored also in vivo for preliminary anticonvulsant activity by using the 6-Hz seizure test and pentylenetetrazol (PTZ) seizure test in mice. The Z-isomer has exhibited higher potency compared to E-isomer most pronouncedly in the 6 Hz test for psychomotor seizures where the compound had activity at all three tested doses. It was found that the Z-isomer decrease the latency for onset of clonic seizures induced by PTZ. These results demonstrate that the Z-isomer deserves further evaluation in other screening tests for anticonvulsant activity.

Amino-terminal dimerization of peptides on the solid support. Synthesis and biological activity of the immunosuppressive HLA-DR fragments linked by poly(ethylene glycol)s

The nonapeptide fragment of the HLA-DR molecule, located in the exposed loop of the beta chain (164-172) and having the sequence VPRSGEVYT, suppresses the immune response. On the basis of the three-dimensional structure of the HLA-DR superdimer, we designed new dimeric analogs in which the VPRSGEVYT peptides are linked through their N-termini by poly(ethylene glycol) linkers of different lengths and are able to mimic the dimeric nature of the immunosuppressive fragments of HLA class II molecules. The analogs were synthesized using standard solid-phase peptide synthesis protocols. The dimerization was achieved by cross-linking the N-terminal positions of the peptides, attached to an MBHA resin, with alpha,omega-bis(acetic acid) poly(ethylene glycol), activated by esterification with pentafluorophenol. Our results demonstrate that the amino-terminal dimerization of the peptide results in enhanced immunosuppressive activity and that the potency of the conjugates depends on the length of the poly(ethylene glycol) linker. MS/MS analysis of the obtained dimeric peptides is also presented.

Dimerization of the immunosuppressive peptide fragment of HLA-DR molecule enhances its potency

Our previous studies revealed that the nonapeptide fragment of HLA-DR molecule, located in the beta chain 164-172 with the VPRSGEVYT sequence, suppresses the immune responses. The sequence is located on the exposed molecule loop, therefore it may be involved in the interactions with other proteins. We suggested that the loop may serve as a functional epitope on the HLA class II surface for intermolecular binding, and that possible mechanism of biological action of the synthesized peptides is associated with interfering of adhesion of HLA class II molecules to their coreceptors. It has been postulated that oligomerization of the coreceptors is required for stable binding to class II HLA. Based on the crystal dimeric structure of HLA-DR molecules, we designed, and synthesized molecules able to induce the putative coreceptors dimerization. The synthesized series of compounds consisted of two VPRSGEVYT sequences linked through their C-termini by spacers of different length: (VPRSGEVYTGn)2K-NH2 ( n = 4-6). The results demonstrate that the dimerization of the nonapeptide fragment of HLA-DR results in enhanced immunosuppressory properties.

Anxiolytic effects of acute morphine can be modulated by nitric oxide systems

This study was performed to investigate whether nitric oxide (NO) precursor (L-arginine), NO donor (S-nitroso-N-acetylpenicillamine, SNAP) and NO synthase inhibitors [N(G)-nitro-L-arginine-methylester (L-NAME) and N(G)-nitro-L-arginine (L-NOARG)] modulate morphine-induced anxiolytic effects in the plus-maze. L-Arginine (100, 200 and 300 mg kg(-1), i.p.) and SNAP (4, 8 and 10 mg kg(-1), i.p.) reduced the anxiolytic effect of morphine (20 mg kg(-1), s.c.). L-NAME (10, 20 and 40 mg/kg, i.p.) and L-NOARG (10, 15 and 20 mg kg(-1), i.p.) enhanced the anxiolytic effects of morphine (20 mg kg(-1), s.c.). On the other hand, L-arginine and SNAP increased the morphine-induced locomotor activity. L-NAME decreased the morphine-induced locomotor activity, but L-NOARG did not modify the morphine-induced locomotor activity. Therefore, these results suggest that the anxiolytic effects of morphine can be modulated by NO systems.

Neurotransmitter mechanisms in gabapentin antinociception

The present study was done to investigate the neurotransmitter mechanisms involved in gabapentin antinociception in healthy albino rats. The formalin test was used to asses antinociception. Gabapentin (10-120 mg/kg s.c.) decreased the pain score in the formalin test. In order to study the putative neurotransmitter mechanisms involved in gabapentin action, the effect of gabapentin (30 mg/kg s.c.) alone and in rats pretreated with different receptor blockers, e.g. bicuculine, saclofen, naloxone, mecamylamine, atropine, DL-p-chlorophenylalanine methyl ester hydrochloride, glibenclamide, theophylline, and L-arginine was assessed. Gabapentin decreased the pain score, and the ED(50) of gabapentin was 36.8 +/- 8.2 (30.2-43.1) mg/kg s.c. Pretreatment with different receptor blockers did not modify gabapentin (30 mg/kg s.c.) antinociception except for L-arginine which increased the pain score from 1.68 +/- 0.29 (gabapentin) to 2.29 +/- 0.41. Results suggest the involvement of L-arginine nitric oxide pathways in gabapentin antinociception.

Synthesis and pharmacological evaluation of dimer derivatives of the bradykinin receptor antagonist HOE-140

The synthesis and pharmacological evaluation of dimer derivatives of the C-terminal fragments of the potent bradykinin antagonist HOE-140, linked through their N-termini, were performed. The influence of peptide moiety length was studied using the succinyl moiety as a linker. Our attention focused on the dimer of the C-terminal tetrapeptide of HOE-140 (compound JMV 980), which displayed some inhibiting activity (IC50 = 247 nM) for bradykinin B2 receptors. Unexpectedly, it was orally active in inhibiting bradykinin-induced hypotension in the rat. Based on this tetrapeptide dimer model, we synthesized pseudotetrapeptide dimer bradykinin antagonists 29 and 33, which exhibited high affinity (Ki = 76 and 61 nM, respectively) for the human cloned B2 receptor. In addition, compound 29 inhibited bradykinin-induced contraction of the human umbilical vein giving a pKB value of 6.45. Compounds 29 and 33 were selective toward B2 receptors because they did not bind to the cloned human B1 receptor up to 10 microM.

Synthesis and activity of dimeric bradykinin antagonists containing diaminodicarboxylic acid bridge residues

Enhancement of a ligand's interaction with a receptor through presenting the ligand in multimeric form is a topic of general interest. Thus dimerization of single-chain bradykinin antagonist peptides has previously been shown to be beneficial in terms of potency and duration of action. While crosslinking polypeptides at terminal positions using suitable dicarboxylic acids and diamines is comparatively straight-forward synthetically, internal dimerizations are usually achieved through oxidation or double S-alkylations of cysteine residues, resulting in metabolically unfavourable disulphide and thioether cross-links. Using suitably modified standard solid-phase peptide synthesis protocols, dimeric bradykinin antagonist peptides [H-(D-Arg)-Arg-Pro-Hyp-Gly-Phe]2-X-[(D-Phe)-Leu-Arg-OH]2 were synthesized where X corresponds to a L,L-2,7-diaminosuberic or L,L-2,9-diaminosebacic acid residue, respectively. The biological activity of these peptides was comparable to that of conventional dimeric bradykinin antagonists cross-linked through cystine or bis(succinimido)alkyl bridges.

Role of nitric oxide and carbon monoxide in modulating the ACTH response to immune and nonimmune signals

The role played by nitric oxide (NO) and carbon monoxide (CO) was explored in the adult male rat by determining whether antagonizing the activity of the enzymes responsible for the formation of these gases altered the response of the hypothalamic-pituitary-adrenal (HPA) axis to immune (cytokines) or nonimmune (mild electroshocks) signals. The arginine derivative Nomeganitro-L-arginine-methylester (L-NAME), which inhibits all three NO synthase (NOS) isoforms [inducible (i), endothelial (e) and neuronal (n)] significantly augments the ACTH response to blood-borne cytokines, but decreases it in rats exposed to shocks or other physico-emotional stresses. The effect of L-NAME in both models is mimicked by L-nitroarginine (L-NNA) and L-nitromethylarginine (L-NMMA), which block constitutive (e and n) forms of NOS, but not by aminoguanidine (which blocks iNOS) or 7-nitroindazole (which specifically blocks nNOS). Despite the ability of L-NAME to markedly augment the stimulatory effect of vasopressin on ACTH secretion, removal of this peptide does not interfere with the interaction between L-NAME and systemically administered interleukin-1beta (IL-1beta). In contrast, blockade of prostaglandin formation prevents both the stimulatory effect of IL-1beta on ACTH release, and its potentiation by L-NAME. In contrast to the investigation of the importance of endogenous NO, studies focused on the role of CO remain scarce. Our preliminary results suggest that while blockade of the formation of this gas decreases the ACTH response to various stimuli, it also significantly interferes with the effect of L-NAME in rats systemically administered cytokines, and further decreases the ACTH response to shocks in animals also injected with arginine analogs. These results indicate the possible presence of functional interactions between NO and CO in regulating the activity of the HPA axis. Our present working hypothesis is that in the presence of elevated circulating cytokine levels, endogenous NO acts presynaptically to inhibit the release of ACTH secretagogues from nerve terminals in the infundibulum. As the acute ACTH response to these immune proteins is believed to primarily depend on events taking place within the median eminence, blockade of NO formation results in exaggerated ACTH release. During exposure to shocks and other nonimmune stresses, on the other hand, increased ACTH secretion is primarily due to activation of hypothalamic neurons. In this case, because of the stimulatory influence of endogenous NO on hypothalamic perikarya that manufacture corticotropin-releasing factor (CRF) and/or of the afferents to these neurons, blockade of NOS activity blunts CRF production, and consequently ACTH release. What remains undetermined is the net effect of the opposite influences of NO during long-term exposure to immune or nonimmune stress. Finally, it is possible that the conflicting results reported by investigators who study the role of NO and CO in isolated cell preparations may reflect, at least in part, these opposite effects of NO on different elements of the HPA axis.

Evidence for a role of bradykinin neurons in the control of gonadotropin-releasing hormone secretion

The present study provides evidence of a novel neuronal pathway for the control of GnRH secretion involving bradykinin neurons. Bradykinin neurons were shown by immunohistochemistry to be densely localized in several regions of the brain including the cortex, hippocampus and supraoptic nucleus, as well as two regions critical in the control of GnRH secretion, the organum vasculosum of the lamina terminalis and arcuate nucleus. Bradykinin dose-dependently stimulated GnRH release from male and proestrous female rat hypothalami in vitro. Antagonist studies revealed that bradykinin effects are mediated by the bradykinin B2 receptor. The effect of bradykinin on GnRH release is not mediated by the classical major transmitter, glutamate, as glutamate antagonists had no effect on bradykinin stimulation of GnRH release. Rather, bradykinin appears to act directly on the GnRH neuron as bradykinin stimulated GnRH release directly from immortalized GnRH (GT1-7) neurons in vitro, and immunoblot studies revealed that the bradykinin B2 receptor is present in GT1-7 neurons. The bradykinin B2 receptor was also demonstrated in the rat hypothalamus and pituitary by immunoblotting. Bradykinin-induced exocytosis of GnRH appears to involve activation of the PKC signaling pathway, as a PKC inhibitor blocked bradykinin-induced GnRH release. Finally, bradykinin neurons appear to be important mediators of steroid signals in the hypothalamus to produce the LH surge, as central administration of a B2 antagonist, but not a B antagonist, significantly attenuated the steroid-induced LH surge in the ovariectomized female rat.

Serotonin dimers: application of the bivalent ligand approach to the design of new potent and selective 5-HT(1B/1D) agonists

A series of serotonin dimers of formula 4 in which two serotonin moeities are linked together through their 5-hydroxyl residue has been prepared and evaluated as 5-HT(1B/1D) receptor agonists. Binding experiments at cloned human 5-HT(1B), 5-HT(1D), and 5-HT(1A) receptors show that all of these dimers are very potent ligands at 5-HT(1B/1D) receptors with increased binding selectivity vs the 5-HT(1A) receptor when compared to serotonin. Studies of inhibition of the forskolin-stimulated c-AMP formation mediated by the human 5-HT(1B) receptor (formerly the 5-HT(1Dbeta) receptor) demonstrate that all of these serotonin dimers behave as full agonists. Among them, the piperazide derivatives of bis-serotonin, 4g,j, were also identified as very potent agonists in contracting the New Zealand white rabbit saphenous vein (pD2 = 7.6 in each case compared to 5.8 for sumatriptan). Results analysis supports the hypothesis that the important increase in potency of the serotonin dimers can be attributed to the presence of two serotonin pharmacophores in the same molecule, while the enhanced selectivity for 5-HT(1B/1D) receptor subtypes may be due to the position of the spacer attachment to serotonin.

Bradykinin antagonists: synthesis and in vitro activity of bissuccinimidoalkane peptide dimers

A systematic study on dimerization of the bradykinin (BK) antagonist D-Arg0-Arg1-Pro2-Hyp3-Gly4-Phe5-Ser6-D-Phe 7-Leu8-Arg9 has been performed. Several of the dimeric BK antagonists displayed remarkable activities and long durations of action. Rank order of antagonist potency as a function of dimerization position is as follows: rat uterus 6 > 5 > 0 > 2 > 1 > 3 >> 4,7,8,9; guinea pig ileum 6 > 5 > 3 > 2 > 1 > 0 >> 4,7,8,9. These results suggest that the development of BK antagonists of significant therapeutic potential may be possible using a dimerization strategy that can overcome the heretofore limiting problems of potency and in vivo duration of action.

Homodimeric forms of bombesin act as potent antagonists of bombesin on Swiss 3T3 cells

Two Lys3-bombesin dimers were prepared by crosslinking epsilon-amino groups Lys3-bombesin with noncleavable (glutaraldehyde) and cleavable [dimethyl-3,3'-dithiobispropionimidate (DTBP)] crosslinkers. The dimers were purified by HPLC ion-exchange chromatography and were shown to have retained immunoreactivity with an anti-bombesin monoclonal antibody directed against the C-terminal binding region of bombesin. The glutaraldehyde cross-linked bombesin dimer specifically inhibited binding of 125I-GRP to its receptor on Swiss 3T3 cells. Bombesin, at 0.6-60 nM induced mitogenesis in quiescent Swiss 3T3 cells, whereas, incubation of cells with the glutaraldehyde bombesin dimer at concentrations up to 124 nM did not. In competition assays, the bombesin dimer exhibited a dose dependent inhibition of bombesin-induced mitogenic activity and intracellular Ca++ mobilization. The bombesin dimer was 100 to 1000-fold more potent than D-Phe12Leu14-bombesin and D-Phe12bombesin, respectively, in inhibiting bombesin-induced mitogenesis on quiescent Swiss 3T3 cells. Similarly, the DTBP-bombesin dimer was not mitogenic to Swiss 3T3 cells, however, cleavage of the disulfide crosslinker with DTT of cell bound DTBP dimer restored mitogenic activity. Finally, the glutaraldehyde bombesin dimer also inhibited growth of bombesin receptor positive H345 SCLC cells in vitro. These findings suggest that the dimeric forms of bombesin are potent antagonists of bombesin.

Characterization of tachykinin receptors in endothelial cells of porcine artery

The binding of iodine-labeled Bolton-Hunter substance P (125I-BHSP) to porcine endothelial cell membranes was examined. The endothelial cells had a single high-affinity binding site with a dissociation constant of 0.10 nM, and a maximum number of binding sites of 52.2 fmol/mg protein. The relative potencies of various tachykinins to displace the binding of 47 pM 125I-BHSP suggested that endothelial cells of porcine aorta contain the NK-1 subtype of tachykinin receptor. A GTP analogue, guanyl-5'-yl imidodiphosphate, induced marked reduction in the number of 125I-BHSP binding sites suggesting that these binding sites are coupled with GTP-binding protein.