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      Anticonvulsant effects of isomeric nonimidazole histamine H 3 receptor antagonists

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          Phenytoin (PHT), valproic acid, and modern antiepileptic drugs (AEDs), eg, remacemide, loreclezole, and safinamide, are only effective within a maximum of 70%–80% of epileptic patients, and in many cases the clinical use of AEDs is restricted by their side effects. Therefore, a continuous need remains to discover innovative chemical entities for the development of active and safer AEDs. Ligands targeting central histamine H 3 receptors (H 3Rs) for epilepsy might be a promising therapeutic approach. To determine the potential of H 3Rs ligands as new AEDs, we recently reported that no anticonvulsant effects were observed for the ( S)-2-(4-(3-(piperidin-1-yl)propoxy)benzylamino)propanamide ( 1). In continuation of our research, we asked whether anticonvulsant differences in activities will be observed for its R-enantiomer, namely, ( R)-2-(4-(3-(piperidin-1-yl)propoxy)benzylamino)propaneamide ( 2) and analogs thereof, in maximum electroshock (MES)-, pentylenetetrazole (PTZ)-, and strychnine (STR)-induced convulsion models in rats having PHT and valproic acid (VPA) as reference AEDs. Unlike the S-enantiomer ( 1), the results show that animals pretreated intraperitoneally (ip) with the R-enantiomer 2 (10 mg/kg) were moderately protected in MES and STR induced models, whereas proconvulsant effect was observed for the same ligand in PTZ-induced convulsion models. However, animals pretreated with intraperitoneal doses of 5, 10, or 15 mg/kg of structurally bulkier ( R)-enantiomer ( 3), in which 3-piperidinopropan-1-ol in ligand 2 was replaced by (4-(3-(piperidin-1-yl)propoxy)phenyl)methanol, and its ( S)-enantiomer ( 4) significantly and in a dose-dependent manner reduced convulsions or exhibited full protection in MES and PTZ convulsions model, respectively. Interestingly, the protective effects observed for the ( R)-enantiomer ( 3) in MES model were significantly greater than those of the standard H 3R inverse agonist/antagonist pitolisant, comparable with those observed for PHT, and reversed when rats were pretreated with the selective H 3R agonist R-(α)-methyl-histamine. Comparisons of the observed antagonistic in vitro affinities among the ligands 16 revealed profound stereoselectivity at human H 3Rs with varying preferences for this receptor subtype. Moreover, the in vivo anticonvulsant effects observed in this study for ligands 16 showed stereoselectivity in different convulsion models in male adult rats.

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          Most cited references 54

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          Critical review of current animal models of seizures and epilepsy used in the discovery and development of new antiepileptic drugs.

          Animal models for seizures and epilepsy have played a fundamental role in advancing our understanding of basic mechanisms underlying ictogenesis and epileptogenesis and have been instrumental in the discovery and preclinical development of novel antiepileptic drugs (AEDs). However, there is growing concern that the efficacy of drug treatment of epilepsy has not substantially improved with the introduction of new AEDs, which, at least in part, may be due to the fact that the same simple screening models, i.e., the maximal electroshock seizure (MES) and s.c. pentylenetetrazole (PTZ) seizure tests, have been used as gatekeepers in AED discovery for >6 decades. It has been argued that these old models may identify only drugs that share characteristics with existing drugs, and are unlikely to have an effect on refractory epilepsies. Indeed, accumulating evidence with several novel AEDs, including levetiracetan, has shown that the MES and PTZ models do not identify all potential AEDs but instead may fail to discover compounds that have great potential efficacy but work through mechanisms not tested by these models. Awareness of the limitations of acute seizure models comes at a critical crossroad. Clearly, preclinical strategies of AED discovery and development need a conceptual shift that is moving away from using models that identify therapies for the symptomatic treatment of epilepsy to those that may be useful for identifying therapies that are more effective in the refractory population and that may ultimately lead to an effective cure in susceptible individuals by interfering with the processes underlying epilepsy. To realize this goal, the molecular mechanisms of the next generation of therapies must necessarily evolve to include targets that contribute to epileptogenesis and pharmacoresistance in relevant epilepsy models. Copyright © 2011 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
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            Auto-inhibition of brain histamine release mediated by a novel class (H3) of histamine receptor.

            Although histaminergic neurones have not yet been histochemically visualized, there is little doubt that histamine (HA) has a neurotransmitter role in the invertebrate and mammalian central nervous system. For example, a combination of biochemical, electrophysiological and lesion studies in rats have shown that histamine is synthesized in and released from a discrete set of neurones ascending through the lateral hypothalamic area and widely projecting in the telencephalon. Histamine acts on target cells in mammalian brain via stimulation of two classes of receptor (H1 and H2) previously characterized in peripheral organs and probably uses Ca2+ and cyclic AMP, respectively, as second messengers. It is well established that several neurotransmitters affect neuronal activity in the central nervous system through stimulation not only of postsynaptic receptors, but also of receptors located presynaptically which often display distinct pharmacological specificity and by which they may control their own release. Such 'autoreceptors' have been demonstrated (or postulated) in the case of noradrenaline, dopamine, serotonin, acetylcholine and gamma-aminobutyric acid (GABA) neurones but have never been demonstrated for histamine. We show here that histamine inhibits its own release from depolarized slices of rat cerebral cortex, an action apparently mediated by a class of receptor (H3) pharmacologically distinct from those previously characterized, that is, the H1 and H2 receptors.
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              Bioorganometallic chemistry of ferrocene.


                Author and article information

                Drug Des Devel Ther
                Drug Des Devel Ther
                Drug Design, Development and Therapy
                Drug Design, Development and Therapy
                Dove Medical Press
                07 November 2016
                : 10
                : 3633-3651
                [1 ]Department of Pharmacology and Therapeutics, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates
                [2 ]Biocenter, Institute of Pharmaceutical Chemistry, Goethe University, Frankfurt, Germany
                [3 ]Department of Pharmaceutical and Medicinal Chemistry, Institute of Pharmaceutical and Medicinal Chemistry, Heinrich Heine University, Düsseldorf, Germany
                Author notes
                Correspondence: Bassem Sadek, Department of Pharmacology and Therapeutics, College of Medicine and Health Sciences, United Arab Emirates University, Al-Ain PO Box 17666, United Arab Emirates, Tel +971 3 713 7512, Fax +971 3 767 2033, Email bassem.sadek@ 123456uaeu.ac.ae
                Holger Stark, Institute of Pharmaceutical and Medicinal Chemistry, Department of Pharmaceutical and Medicinal Chemistry, Heinrich Heine University, Universitaetsstr 1, Düsseldorf 40225, Germany, Tel +49 211 811 0478, Fax +49 211 811 3359, Email stark@ 123456hhu.de
                © 2016 Sadek et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

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