Littérature scientifique sur le sujet « Imidazoline-2 receptors »

Imidazolines are a valuable class of organic compounds, namely ligands of imidazoline receptors, chiral ligands for metal catalysis, synthetic intermediates. The title compound has been prepared through a modified procedure, employing N-benzylethylenediamine and thiophene-2-carbaldehyde under the action of N-bromosuccinimide (NBS) in dichloromethane (DCM) in a good 78% yield.

Background Dexmedetomidine (Precedex; Abbott Laboratories, Abbott Park, IL) is a selective alpha2-adrenergic agonist that also has affinity for imidazoline receptors. In clinical studies, dexmedetomidine has sedative effects and impairs memory, but the action of dexmedetomidine on synaptic plasticity in the brain has yet to be established. In the present study, the authors investigated the effects of dexmedetomidine on two forms of synaptic plasticity-long-term potentiation (LTP) and paired-pulse facilitation-in the CA1 region of mouse hippocampal slices. Methods The authors recorded Schaffer collateral-evoked field excitatory postsynaptic potentials from mouse hippocampal slices in CA1 stratum radiatum. The slope of the rising phase of the field excitatory postsynaptic potential was used to estimate the strength of synaptic transmission. Results Application of dexmedetomidine for 20 min before "theta burst" stimulation dose-dependently attenuated LTP, and half-inhibitory concentration of dexmedetomidine was 28.6 +/- 5.7 nm. The inhibitory effect of dexmedetomidine on LTP was not abolished by an alpha2-adrenoceptor antagonist (yohimbine), an imidazoline type 1 receptor and alpha2-adrenoceptor antagonist (efaroxan), an alpha1-adrenoceptor antagonist (prazosin), or a gamma-aminobutyric acid type A receptor antagonist (picrotoxin). However, an imidazoline type 2 receptor and alpha2-adrenoceptor antagonist (idazoxan) completely blocked the dexmedetomidine-induced attenuation. Furthermore, 2-benzofuranyl-2-imidaloline, a selective imidazoline type 2 receptor ligand, reduced LTP. 2-(4,5-dihydroimidaz-2-yl)-quinoline, another imidazoline type 2 receptor ligand, abolished the 2-benzofuranyl-2-imidaloline-induced attenuation, but the inhibitory effect of dexmedetomidine on LTP was not abolished by 2-(4,5-dihydroimidaz-2-yl)-quinoline. Dexmedetomidine did not affect paired-pulse facilitation. Conclusion Dexmedetomidine impairs LTP in area CA1 of the mouse hippocampus via imidazoline type 2 receptors and alpha2-adrenoceptors.

Imidazoline receptor agonists are one of the groups of contemporary antihypertensive drugs with the pleiotropic cardiovascular effects. In this review, the historical, physiological, pathophysiological aspects concerning imidazoline receptor agonists and possible mechanisms for their participation in endothelioprotection were considered. Illuminated the molecular biology of each subtype of imidazoline receptors and their significance in the pharmacological correction of cardiovascular disease. IR type 1 are localized in the brain nucleus, carrying out the descending tonic control of sympathetic activation, as well as in the endothelial cells of the vessels and kidneys. Their activation leads to a decrease in blood pressure, slowing the remodeling of the vascular wall and increasing sodium nares. IR type 2 is expressed predominantly in the adrenal gland, fat and muscle tissues. The physiological effects of their stimulation are associated with an increase in glucose utilization by peripheral tissues. IR type 3 are mainly present in pancreatic cells and are associated with the regulation of insulin secretion. Their stimulation leads to an increase in insulin liberation. Thus, IR agonists are able to improve endothelial function through various mechanisms, including blood pressure reduction, improvement in metabolic profile, and direct positive effects on the vascular wall. Current information on the pharmacological effects of this group compounds allows us to conclude that they are a promising group for correcting endothelial dysfunction and complications associated with it.

Goal of this study was the synthesis of new structurally related imidazoline molecules direct to selectively interact with a2-Adrenoreceptors (a2-ARs) or I2-Imidazoline Binding Sites (I2-IBS). The rational design of these new compounds held in due consideration all the indications emerged by previous investigations, among them: i) the observation that essential requirement for α2-ARs/I2-IBS discrimination was the presence of an oxyethyl or ethylenic chain, respectively, between the aromatic portion and imidazoline nucleus; ii) the hypothesys that α2-ARs and I2-IBS could present analogies in the nature and orientation of some critical binding functions. The obtained ligands proved to be useful tools for the respective system characterization. In both systems it was demonstrated that the introduction of pendent groups in the basic structure phenyl ring of some studied leads was able to induce a drastic change of their biological profile. In fact, known α2-ARs antagonists, such as 1 and idazoxan, changed into efficient agonists, sometimes, endowed with significant α2C-AR selectivity (Section 1A). Moreover, highlighting the critical role played by chirality in the activation of α2C-AR subtype, still defined enigmatic, it was showed that the ligand required stereochemical characteristics were strongly dependent on the nature of the pendent group in ortho position of the phenyl ring. In fact, a surprising reversal of enantioselectivity was observed for similar compounds biphenyline and m-nitro-biphenyline, whose preferred α2C configurations proved (S)-(-) and (R)-(+) forms, respectively (section 1B). Many opiate drugs, such as morphine, are commonly used for pain relief, but their usefulness in prolonged use is limited by the development of tolerance and dependence. Since several studies indicated that the possible synergism with I2-IBS-mediated antinociceptive mechanisms could enhance the morphine analgesia and attenuate its side effects, new I2-IBS ligands have been prepared. All the new compounds displayed interesting I2-IBS affinity and significant I2-IBS selectivity with respect to I1-IBS and α2-ARs. As aforementioned, the introduction of substituents in the aromatic ring induced a significant change of biological profile. In fact, the compounds lacking in or endowed with pendent groups produced enhancement (positive modulation) or decrease (negative modulation), respectively, of morphine analgesia. Interestingly, both modulations appeared useful to attenuate the side effects development. In particular, phenyzoline (1, displaying positive modulation) and compound 9 (displaying negative modulation) proved able to significantly attenuate the development of tolerance and dependence, respectively (2A and 2B Sections). Finally, the comparative study of some rationally designed compounds pointed out some significant analogies between the hydrophobic domain of I2-IBS proteins binding site and aromatic cluster of α2C-AR binding site cavity.

Bortezomib (BTZ) is a proteasome inhibitor that shows potent antineoplastic effects mainly in the treatment of the multiple myeloma. However, BTZ induces a painful neuropathy that causes a significant impairment of patient’s quality of life. CR4056 is a novel imidazoline-2 (I2) ligand that acts modulating the levels of monoamino oxidase (MAO), and it is characterized by a relevant efficacy in several animal models of pain. This study was designed to test the efficacy of CR4056 in a chronic model of BTZ-induced neurotoxicity, compared with two well known analgesic, buprenorphine and gabapentin. Besides, the effect of CR4056 in preventive and therapeutic schedule was evaluated. After 8 weeks of treatment, BTZ reduced nerve conduction velocity (NCV) and induced allodynia. CR4056, gabapentin or buprenorphine in neuropathic animals did not reverse the impaired NCV. By contrast, the optimal CR4056 dose reversed BTZ-induced allodynia. This effect was persistent along the treatment period without rebound after suspension. These results promote the use of CR4056 as a potential treatment in the chronic neuropathic pain therapy.

Clonidine, an _2-adrenergic receptor agonist, is a classic pharmacological tool used to study the sympathetic control of cardiovascular and thermoregulatory processes. Clonidine's ability to inhibit sympathetic output may be linked more to its affinity for non-adrenergic I1-imidazoline receptors than for _2-adrenoceptors. Previous research has focused on the role of medullary _2-adrenergic and I 1-imidazoline receptors in regulating blood pressure; yet, structures rostral to the brainstem also influence sympathetic output. What role I 1-imidazoline receptors located in the medulla, or those located in the region of the third ventricle, exert towards the regulation of body temperature is largely unexplored. The present study assessed the relative contributions of diencephalic and medullary _2-adrenergic and I1-imidazoline receptors on core body temperature in conscious rats. In Experiment 1, 24 rats received chronically indwelling thermistors, for recording body temperature, and intracerebroventricular (ICV)cannulae targeted to the third ventricle, an area near the hypothalamus, for drug administration. In a repeated measures design, 12 rats were pretreated with central administration of 4 [mu]l of saline or efaroxan, an I1-antagonist; 20-min later moxonidine, an I1 agonist, was centrally administered in l of 3 doses (0, 1, 10 nmol) delivered in a 4 [mu]l saline over 45-60 s. The other 12 rats were similarly pretreated with saline or SK&F 86466, an _2 -adrenergic receptor antagonist, followed 20 min later with 1 of 3 doses (0, 1, 10 nmol) of UK 14304, an a2-adrenergic receptor agonist. Body temperature was monitored at 30-min intervals for 4 hr. The result were contrary to what might have been predicted from reports of moxonidine-induced reductions in blood pressure in that 10-nmol of moxonidine increased core body temperature (>1.5C, 'p' < .02). However, the increase in body temperature was reversed with efaroxan. UK 14304 did not alter body temperature. In Experiment 2, 24 rats underwent the same procedure as described above, except the drugs were delivered to the fourth ventricle, an area near the medulla. In this case, neither moxonidine nor UK 14304 had any significant effect on body temperature. These findings support the notion that I 1-imidazoline and _2-adrenergic receptors in the diencephalon and medulla are functionally distinct, and that the thermoregulatory contribution of diencephalic I1-imidazoline receptors is different from what would be predicted from their sympathoinhibitory action exhibited in the medulla.

The imidazoline I1 receptor (I1-R) is a novel receptor found primarily in the brain and nervous tissue where it modulates neurotransmission. It is named for its high affinity for compounds with an imidazoline structure such as the anti-hypertensive drugs, clonidine and moxonidine. The imidazoline receptor antisera-selected protein (IRAS) is the putative clone of the I1-R. IRAS has a unique structure, which does not resemble any other receptor protein. IRAS is present throughout the body with highest levels in the brain. There is a growing body of research examining the physiological roles of IRAS as an I1-R, in cell survival, migration and protein trafficking. However, there is little research into its neuronal functions. IRAS interacts with other membrane receptors: the mouse homologue of IRAS reorganises the actin cytoskeleton through interaction with the α5β1 fibronectin receptor. IRAS also binds insulin receptor substrate 4 and enhances insulin-induced extracellular signal-regulated kinase1/2 (ERK1/2) activation. Actin reorganisation and ERK1/2 activation are important for the development of neurites during neuronal differentiation. Therefore, the work described in this thesis aimed to investigate the effects of IRAS on neuronal differentiation. Studies reported in this thesis also aimed to investigate whether IRAS affected ERK1/2 signalling of other receptors involved in neuronal differentiation such as the NGF receptor, TrkA, and lysophospholipid receptors. The above aims were carried out in neuronal model PC12 cells transfected with either IRAS or a vector plasmid. Fluorescence microscopy and Western blotting techniques were used to examine the effect of IRAS on cell morphology and ERK1/2 signalling. The work described in this thesis found that IRAS reorganises the actin cytoskeleton and enhances growth cone development in PC12 cells. This study also shows that IRAS differentially enhances or inhibits NGF-induced PC12 cell differentiation depending on the presence or absence of serum in the media. In full-serum conditions, IRAS enhanced neurite outgrowth and this was accompanied by an increase in ERK1/2 activation. In serum-starved cells, IRAS inhibited neurite outgrowth with similar levels of ERK1/2 activation observed in vector- and IRAS-transfected cells. Finally, studies presented in this thesis found that IRAS enhances lysophosphatidic acid-induced ERK1/2 activation and that IRAS interacting with lysophospholipid receptor agonists present in serum is a potential mechanism by which it enhances NGF-induced ERK1/2 activation in full-serum conditions.
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Thesis (Ph.D.) - University of Adelaide, School of Medical Sciences, 2008

Les azapeptides sont des mimes peptidiques où le carbone alpha d’un ou de plusieurs acides aminés est remplacé par un atome d’azote. Cette modification tend à stabiliser une conformation en repliement beta en raison de la répulsion électronique entre les paires d’électrons libres des atomes d’azote adjacents et de la géométrie plane de l’urée. De plus, le résidu semicarbazide a une meilleure résistance face aux protéases en plus d’être chimiquement plus stable qu’une liaison amide. Bien que les propriétés des azapeptides en fassent des mimes peptidiques intéressants, leurs méthodes de synthèses font appel à la synthèse laborieuse d’hydrazines substituées en solution. Le peptide sécréteur d’hormone de croissance 6 (GHRP-6, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) est un hexapeptide synthétique qui possède une affinité pour deux récepteurs distincts: les récepteurs GHS-R1a et CD36. Les travaux effectués au cours de mon doctorat qui seront détaillés dans cet ouvrage visent à atteindre deux objectifs: (1) le développement d’analogues du peptide GHRP-6 sélectif à un seul récepteur et (2) la mise au point d’une nouvelle méthodologie pour la synthèse combinatoire d’azapeptides. En réponse au premier objectif, la synthèse parallèle de 49 analogues aza-GHRP-6 a été effectuée et certains candidats sélectifs au récepteur CD36 ont été identifiés. L’étude de leurs propriétés anti-angiogéniques, effectuée par nos collaborateurs, a également permis d’identifier des candidats intéressants pour le traitement potentiel de la dégénérescence maculaire liée à l’âge. Une nouvelle approche pour la synthèse combinatoire d’azapeptides, faisant appel à l’alkylation et la déprotection chimiosélective d’une sous-unité semicarbazone ancrée sur support solide, a ensuite été développée. La portée de cette méthodologie a été augmentée par la découverte de conditions permettant l’arylation régiosélective de cette sous-unité semicarbazone, donnant accès à treize nouveaux dérivés aza-GHRP-6 possédant des résidus aza-arylglycines aux positions D-Trp2 et Trp4. L’élaboration de conditions propices à l’alkylation et la déprotection chimiosélective de la semicarbazone a donné accès à une variété de chaînes latérales sur l’acide aminé « aza » préalablement inaccessibles. Nous avons, entre autres, démontré qu’une chaîne latérale propargyl pouvait être incorporée sur l’acide aminé « aza ». Tenant compte de la réactivité des alcynes, nous avons ensuite élaboré des conditions réactionnelles permettant la formation in situ d’azotures aromatiques, suivie d’une réaction de cycloaddition 1,3-dipolaire sur support solide, dans le but d’obtenir des mimes de tryptophane. Sept analogues du GHRP-6 ont été synthétisés et testés pour affinité au récepteur CD36 par nos collaborateurs. De plus, nous avons effectué une réaction de couplage en solution entre un dipeptide possédant un résidu aza-propargylglycine, du paraformaldehyde et une variété d’amines secondaires (couplage A3) afin d’accéder à des mimes rigides d’aza-lysine. Ces sous-unités ont ensuite été incorporées sur support solide afin de générer sept nouveaux azapeptides avec des dérivés aza-lysine à la position Trp4 du GHRP-6. Enfin, une réaction de cyclisation 5-exo-dig a été développée pour la synthèse de N-amino imidazolin-2-ones en tant que nouveaux mimes peptidiques. Leur fonctionnalisation par une série de groupements benzyliques à la position 4 de l’hétérocycle a été rendue possible grâce à un couplage Sonogashira précédant la réaction de cyclisation. Les propriétés conformationnelles de cette nouvelle famille de composés ont été étudiées par cristallographie aux rayons X et spectroscopie RMN d’un tétrapeptide modèle. L’activité biologique de deux mimes peptidiques, possédant un résidu N-amino-4-méthyl- et 4-benzyl-imidazolin-2-one à la position Trp4 du GHRP-6, a aussi été examinée. L’ensemble de ces travaux devrait contribuer à l’avancement des connaissances au niveau des facteurs structurels et conformationnels requis pour le développement d’azapeptides en tant que ligands du récepteur CD36. De plus, les résultats obtenus devraient encourager davantage l’utilisation d’azapeptides comme peptidomimétiques grâce à leur nouvelle facilité de synthèse et la diversité grandissante au niveau de la chaîne latérale des acides aminés « aza ».
Azapeptides are peptide mimics in which the CH alpha in one or more amino acids has been replaced with a nitirogen atom. Such a modification tends to induce beta turn conformations in peptides, because of the consequences of lone–pair lone–pair repulsion between the two adjacent nitrogens and the planar geometry of the urea in the semicarbazide moiety. Furthermore, the semicarbazide increases protease resistance and is chemically more stable than its amide counterpart. Despite the potential advantages of using azapeptides mimics, their synthesis has been hampered by the solution-phase construction of substituted hydrazines prior to their incorporation into peptide sequences. Growth Hormone Releasing Peptide 6 sequence (GHRP-6, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) is a synthetic hexapeptide that binds to two distinct receptor: the Growth Hormone Secretatgogue Receptor 1a (GHS-R1a) and the Cluster of Differentiation 36 (CD36) receptor. The body of my Ph.D thesis has been generally targeted towards two objectives: (a) the development of azapeptide analogs of GHRP-6 with enhanced receptor selectivity and (b) the elaboration of a new synthetic approach for combinatorial submonomer azapeptide synthesis. In response to the first objective, 49 aza-GHRP-6 derivatives were synthesized and evaluated for receptor binding and biological activity. From this library, certain candidates were identified which exhibited decreased affinity for the GHS-R1a receptor with maintained affinity for the CD36 receptor. Furthermore, in studying their anti-angiogenic properties, our collaborators have identified aza-GHRP-6 analogs, which caused a marked decrease in microvascular sprouting in choroid explants, as well as another displaying potential to increase angiogenesis. A new approach for the combinatorial synthesis of azapeptides was developed to better conduct SAR studies using azapeptides. This method features the chemoselective alkylation and deprotection of a resin-bound semicarbazone building block. The scope of the methodology was further expanded by the development of reaction conditions for the chemoselective N-arylation of this semicarbazone residue, yielding 13 aza-GHRP-6 derivatives with aza-arylglycines residues at the D-Trp2 and Trp4 positions. The elaboration of a methodology based on the chemoselective alkylation and deprotection of a semicarbazone has allowed for greater aza-amino acid side chain diversity, enabling for example, the efficient incorporation of aza-propargylglycine residues into peptide sequences. Considering the reactivity of alkynes, we developed reaction conditions for in situ formation of aromatic azides, followed by a 1,3-dipolar cycloaddition reaction on solid support to yield aza-1-aryl,2,3-triazole-3-alanine residues as tryptophan mimics. Seven aza-GHRP-6 analogs were synthesized and subsequently tested for binding to the CD36 receptor by our collaborators. Moreover, the coupling reaction between an aza-propargylglycine-containing dipeptide building block, paraformaldehyde and a variety of secondary amines (A3 coupling) was accomplished in solution to provide access to rigid aza-lysine mimics. These aza-dipeptides were subsequently incorporated at the Trp4 position of seven new aza-GHRP-6 analogues using a solid-phase protocol, and the resulting azaLys mimics were tested for binding towards the CD36 receptor. Finally, conditions for a 5-exo-dig cyclization of an aza-propargylglycine residue were developed to give N-amino imidazolin-2-ones as turn-inducing peptide mimics. Their modification at the 4 position was achieved using a Sonogashira coupling protocol prior to the cyclization step. The conformational properties of these new heterocyclic motifs were assessed by X-ray crystallography and NMR spectroscopy on a tetrapeptide model system. The incorporation of N-amino-4-methyl- and 4-benzyl-imidazolin-2-ones at the Trp4 position of GHRP-6 was further accomplished and the biological evaluation of the peptidomimetics was examined. Taken together, these results should lead to a better understanding of the structural and conformational factors responsible for binding and biological activity of azapeptide ligands of the CD36 receptor. Furthermore, the submonomer approach for azapeptide synthesis developed should promote the use of azapeptides as peptide mimics, given its accessibility and the increased aza-amino acid side-chain diversity available.