Sodium Channel Blocking Activity Research Articles

Effect of Linker Elongation on the VGSC Affinity and Anticonvulsant Activity among 4-Alkyl-5-aryl-1,2,4-triazole-3-thione Derivatives

The main aim of the current project was to investigate the effect of the linker size in 4-alkyl-5-aryl-1,2,4-triazole-3-thione derivatives, known as a group of antiepileptic drug candidates, on their affinity towards voltage-gated sodium channels (VGSCs). The rationale of the study was based both on the SAR observations and docking simulations of the interactions between the designed ligands and the binding site of human VGSC. HYDE docking scores, which describe hydrogen bonding, desolvation, and hydrophobic effects, obtained for 5-[(3-chlorophenyl)ethyl]-4-butyl/hexyl-1,2,4-triazole-3-thiones, justified their beneficial sodium channel blocking activity. The results of docking simulations were verified using a radioligand binding assay with [3H]batrachotoxin. Unexpectedly, although the investigated triazole-based compounds acted as VGSC ligands, their affinities were lower than those of the respective analogs containing shorter alkyl linkers. Since numerous sodium channel blockers are recognized as antiepileptic agents, the obtained 1,2,4-triazole derivatives were examined for antiepileptic potential using an experimental model of tonic–clonic seizures in mice. Median effective doses (ED50) of the compounds examined in MES test reached 96.6 ± 14.8 mg/kg, while their median toxic doses (TD50), obtained in the rotarod test, were even as high as 710.5 ± 47.4 mg/kg.

Erythromelalgia: Definition, clinical contexts, differential diagnosis, and therapy. Single case and literature update

Clinical publications on this morbid condition report as many as 16 different Nav1 7 channel substitutions. They also report more than 40 pharmacological treatments, including agents with sodium channel blocking but nonspecific activity (mexiletine, lidocaine, carbamazepine), anti-neuropathic drugs (gabapentinoids and antidepressants), antidepressant drugs with efficacy on migraines (amitriptyline) vasoactive drugs for the management of hypertension, and analgesics (opioids and ketamine). Current research fails to address all patients’ clinical needs, although it recently suggests new genetic hypotheses yet to be tested and the central importance of genetic counseling, to inform patients and their families about the severity, likely course of symptoms, and risk of complications, and in some cases to guide clinical management. Current findings and the significant morbidity associated with the condition, even in light of the single case presented, highlight the need for mechanism-based therapies to improve clinical outcomes.

Voltage-Gated Sodium Channel Blockers: Synthesis of Mexiletine Analogues and Homologues.

Mexiletine is an antiarrhythmic drug belonging to IB class, acting as sodium channel blocker. Besides its well-known activity on arrhythmias, its usefulness in the treatment of myotonia, myotonic dystrophy and amyotrophic lateral sclerosis is now widely recognized. Nevertheless, it has been retired from the market in several countries because of its undesired effects. Thus, several papers were reported in the last years about analogues and homologues of mexiletine being endowed with a wider therapeutic ratio and a more selectivity of action. Some of them showed sodium channel blocking activity higher than the parent compound. It is noteworthy that mexiletine is used in therapy as a racemate even though a difference in the activities of the two enantiomers was widely demonstrated, with (-)-(R)-enantiomer being more active: this finding led several research groups to study mexiletine and its analogues and homologues in their optically active forms. This review summarizes the different synthetic routes used to obtain these compounds. They could represent an interesting starting point to new mexiletine-like compounds without common side effects related to the use of mexiletine.

Influence of propafenone on the anticonvulsant activity of various novel antiepileptic drugs in the mouse maximal electroshock model.

The main mechanism of action of propafenone (antiarrhythmic drug) involves the inhibition of the fast inward sodium current during phase 0 of the action potential. Sodium channel-blocking activity is also characteristic for some antiepileptic drugs. Therefore, it could be assumed that propafenone may also affect seizures. In the present study, we evaluated the effect of propafenone on the protective effect of oxcarbazepine, lamotrigine, topiramate and pregabalin against the maximal electroshock-induced seizures in mice. Anticonvulsant activity of propafenone was assessed with the maximal electroshock seizure threshold (MEST) test. Influence of propafenone on the anticonvulsant activity of antiepileptic drugs was estimated in the mouse maximal electroshock model (MES). Drug-related adverse effects were determined in the chimney test (motor coordination) and passive-avoidance task (long-term memory). Brain concentrations of antiepileptics were assessed by fluorescence polarization immunoassay. Propafenone at doses 60-90mg/kg significantly increased the threshold of seizures, in turn at doses 5-50mg/kg did not affect this parameter. Administration of propafenone at the subthreshold dose of 50mg/kg increased antielectroshock activity of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine. As regards adverse effects, propafenone alone and in combination with antiepileptic drugs did not significantly impair motor coordination or long-term memory in mice. Propafenone (50mg/kg) significantly increased the brain level of pregabalin. Brain concentrations of topiramate and oxcarbazepine were not affected. Our findings show that propafenone has own anticonvulsant action and enhances efficacy of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine, at least in experimental condition.

Sodium Channel Blocking Activity and In-vivo Testing of New Phenylimidazole Derivatives

We previously reported the discovery of diphenylimidazoles as potent sodium channel blockers, potentially useful in the treatment of epilepsy. In this work we further explore the structural requirements necessary for the potency of these derivatives with the aim to understand which structural modifications of the original scaffold could be tolerated in order to retain activity. We have synthesized new compounds working on the 2-position of the imidazole ring. First we have introduced a carbonyl spacer, that was subsequently reduced to alcohol. Both carbonyl and alcohol derivatives have been tested for their ability to block NaV1.6 sodium channel subtype in vitro and for their antiepileptic activity in rodent acute seizures models. Keywords: Sodium channels, patch clamp electrophysiology, NaV1.6, Phenyl-imidazoles.

Synthesis and biological evaluation of palmyrolide A macrocycles as sodium channel blockers towards neuroprotection.

Palmyrolide A is a neuroprotective macrolide isolated by Gerwick and coworkers in 2010. This natural product is known to suppress neuronal spontaneous calcium ion oscillations through its voltage-gated sodium channel blocking ability which is of significant interest in CNS drug discovery. Herein, we give a detailed account on total synthesis of (+)-palmyrolide A and synthesis of a focused library of macrocycles around the scaffold, followed by their biological evaluation. Use of the chiral pool approach, Zhu's oxidative homologation, access to unnatural cis-palmyrolide A, preparation of 18 new analogues and identification of macrolides with improved sodium channel blocking activity are the important features of the present paper. As a measure of potency as voltage-gated sodium channel blockers, all the synthesized analogues were profiled for their ability to inhibit the veratridine-stimulated Na(+) influx in murine primary neuronal cultures. Four macrocycles were found to be more potent or comparable to that of the natural product (-)-palmyrolide A. The most potent compound from this series 20 was structurally simplified and readily accessible in good quantities for further biological profiling.

An overview on the origin and production of tetrodotoxin, a potent neurotoxin.

Tetrodotoxin (TTX) is a deadly neurotoxin which selectively inhibits Na(+) activation mechanism of nerve impulse, without affecting the permeability of K(+) ions. Because of this sodium channel blocking action, it is majorly being studied for biomedical applications. TTX is present in taxonomically diverse groups of animals inhabiting terrestrial, marine, fresh water and brackish water environments, still its origin remains unclear. The extensive study of the toxin has revealed a few possibilities of its origin. This review reports on the aspects of the origin of TTX, where the primary focus is on its exogenous origin. The significance of bacterial, cellular and environmental factors in its biogenesis and accumulation is also discussed. The possible facets for engineering the bacterial genomics to modulate the gene expression for TTX production are also outlined.

Phenytoin inhibits contractions of rat gastrointestinal and portal vein smooth muscle by inhibiting calcium entry.

Phenytoin is widely used as a second-line treatment for status epilepticus. Besides its well-known cardiac pro-arrhythmogenicity, side effects on other organ systems have received less attention. This study investigates the effects of phenytoin on gastrointestinal tissue function using an invitro model of smooth muscle preparations from rats by combining registrations of pharmacological effects on mechanical contractions, electric field potentials, and dynamic intravital fluorescence microscopy. When added to the bathing solution at a concentration of 30μM, phenytoin reduced the frequency of spontaneous activity significantly in antrum and portal vein preparations to 72.2±36.5% (p=0.022) and 80.7±24.4% (p=0.037) of control values, respectively. At a concentration of 100μM, theheight of spontaneous contractions declined to 9.8±19.6% (p=0.005) (antrum), 15.7±28.2% (p=0.004) (portal vein), and 31.8±31.3% (p= 0.005) (colon) in comparison to the control conditions before the application of phenytoin. Depolarization triggered increases in calcium dependent fluorescence signals were reduced by 52.8±39.1% (p=0.012) The inhibition of spontaneous activity caused by phenytoin was reduced in the presence of the L-type calcium channel agonist BAY K8644(-). Phenytoin exerts strong inhibitory effects on the spontaneous and stimulated contractile activity of smooth muscles from both the upper and lower gastrointestinal tract. The mechanism underlying thiseffect is not related to the sodium channel blocking activity of phenytoin, but is rather causedby an inhibition of calcium entry through voltage dependent L-type calcium channels. The results of this study should raise vigilance to gastrointestinal complications in patients treated with phenytoin.

Isolation of 6-Deoxytetrodotoxin from the Pufferfish, Takifugu pardalis, and a Comparison of the Effects of the C-6 and C-11 Hydroxy Groups of Tetrodotoxin on Its Activity

Identification of new tetrodotoxin (TTX, 1) analogues would be significant in the elucidation of its biosynthetic pathway and a study of its structure-activity relationships. In this study, a new TTX analogue, 6-deoxyTTX (2), was isolated from the ovary of the pufferfish, Takifugu pardalis, and the structure was determined using spectroscopic methods. Compound 2 was also identified in other marine animals, Nassarius snail and blue-ringed octopuses, using LC-MS. Furthermore, we investigated the voltage-gated sodium channel blocking activity of 2 by examination of the inhibitory activities to cytotoxicity induced by ouabain and veratridine in mouse neuroblastoma cells (Neuro-2a). The activities were then compared with those of 1, 11-deoxyTTX (3), and 6,11-dideoxyTTX (4). The EC50 value for 2 was estimated to be 6.5±2.2 nM, approximately 3-fold larger than that of 1 (2.1±0.6 nM) and approximately 20-fold smaller than that of 3. These results suggested that contribution of the C-6 hydroxy group to the activity is less than that of the C-11 hydroxy group.

Improving the Assessment of Heart Toxicity for All New Drugs Through Translational Regulatory Science

Fourteen drugs have been removed from the market worldwide because they cause torsade de pointes. Most drugs that cause torsade can be identified by assessing whether they block the human ether à gogo related gene (hERG) potassium channel and prolong the QT interval on the electrocardiogram. In response, regulatory agencies require new drugs to undergo "thorough QT" studies. However, some drugs block hERG potassium channels and prolong QT with minimal torsade risk because they also block calcium and/or sodium channels. Through analysis of clinical and preclinical data from 34 studies submitted to the US Food and Drug Administration and by computer simulations, we demonstrate that by dividing the QT interval into its components of depolarization (QRS), early repolarization (J-Tpeak), and late repolarization (Tpeak-Tend), along with atrioventricular conduction delay (PR), it may be possible to determine which hERG potassium channel blockers also have calcium and/or sodium channel blocking activity. This translational regulatory science approach may enable innovative drugs that otherwise would have been labeled unsafe to come to market.

Histone deacetylases are required for amphibian tail and limb regeneration but not development

Amphibians such as Xenopus laevis and Ambystoma mexicanum are capable of whole structure regeneration. However, transcriptional control over these events is not well understood. Here, we investigate the role of histone deacetylase (HDAC) enzymes in regeneration using HDAC inhibitors. The class I/II HDAC inhibitor valproic acid (VPA) inhibits tail regeneration in embryos of the anuran amphibian Xenopus laevis, confirming a recent report by others (Tseng et al., 2011). This inhibition correlates with a sixfold reduction in endogenous HDAC activity. VPA also inhibited tail regeneration in post-refractory stage Xenopus larvae and larvae of the urodele A. mexicanum (axolotl). Furthermore, Xenopus limb regeneration was also significantly impaired by post-amputation treatment with VPA, suggesting a general requirement for HDAC activity in the process of appendage regeneration in amphibians. The most potent inhibition of tail regeneration was observed following treatment with VPA during the wound healing, pre-blastema phase. A second HDAC inhibitor, sodium butyrate, was also shown to inhibit tail regeneration. While both VPA and sodium butyrate are reported to block sodium channel function as well as HDACs, regeneration was not inhibited by valpromide, an analogue of VPA that lacks HDAC inhibition but retains sodium channel blocking activity. Finally, although VPA is a known teratogen, we show that neither tailbud nor limb bud development are affected by exposure to this compound. We conclude that histone deacetylation is specifically required for the earliest events in appendage regeneration in amphibians, and suggest that this may act as a switch to trigger re-expression of developmental genes.

Biosynthetically intriguing chlorinated lipophilic metabolites from geographically distant tropical marine cyanobacteria.

Five new vinylchlorine-containing metabolites, the lipoamides janthielamide A and kimbeamides A-C and the ketide-extended pyranone kimbelactone A, have been isolated from collections of marine cyanobacteria made in Curaçao and Papua New Guinea. Both janthielamide A and kimbeamide A exhibited moderate sodium channel blocking activity in murine Neuro-2a cells. Consistent with this activity, janthielamide A was also found to antagonize veratridine-induced sodium influx in murine cerebrocortical neurons. These lipoamides represent the newest additions to a relatively rare family of marine cyanobacterial-derived lipoamides and a new structural class of compounds exhibiting neuromodulatory activities from marine cyanobacteria.

Synthesis and Toxicopharmacological Evaluation of m-Hydroxymexiletine, the First Metabolite of Mexiletine More Potent Than the Parent Compound on Voltage-Gated Sodium Channels

The first synthesis of m-hydroxymexiletine (MHM) has been accomplished. MHM displayed hNav1.5 sodium channel blocking activity, and tests indicate it to be ∼2-fold more potent than the parent mexiletine and to have more favorable toxicological properties than mexiletine. Thus, MHM and possible related prodrugs might be studied as agents for the treatment of arrhythmias, neuropathic pain, and myotonias in substitution of mexiletine (metabolite switch), which has turned out to be tainted with common toxicity.

Cymatherelactone and cymatherols A− C, polycyclic oxylipins from the marine brown alga Cymathere triplicata

An investigation of the oxylipin chemistry of the temperate brown alga Cymathere triplicata led to the isolation of several secondary metabolites, cymatherelactone ( 1) and cymatherols A− C ( 2– 4), the latter as their methyl ester derivatives ( 5– 7), which contained cyclopentyl, cyclopropyl, epoxide and lactone rings. Their structures were elucidated using a combination of spectroscopic techniques and synthetic chemistry. Cymatherelactone ( 1), as well as R- and S-Mosher’s esters of its seco acid, exhibited moderate sodium channel blocking activity.

Main Cavinton® metabolite cAVA increases neuronal excitability

Event Abstract Back to Event Main Cavinton® metabolite cAVA increases neuronal excitability B. Farkas1*, P. Kocsis1, I. Tarnawa1 and K. Tihanyi1 1 Gedeon Richter Plc.,, Pharmacology and Drug Safety Research, Hungary The sodium channel blocking activity of Cavinton (vinpocetine) is implicated in its anti-excitotoxic actions. Clinical- as well as animal experimental data indicate that vinpocetine has a memory enhancing effect. However, inhibition of sodium channels, which decreases excitability, is difficult to reconcile with a positive effect on memory. Vinpocetine is readily metabolised to cis-apovincaminic acid (cAVA) in rats. We investigated if cAVA could play a role in the memory enhancing effect of vinpocetine, by analysing the effects of cAVA on neuronal excitability in models of cortical spreading depression (CSD) and in spinal reflex experiments. In the rat hemisected spinal cord model, ventral root reflexes recorded from the L5 ventral root following the stimulation of the ipsilateral dorsal root, were dose-dependently enhanced by cAVA (25-400 µM). In brain slices, cAVA (100-200 µM) markedly increased the excitability of cortical tissue. CSDs could have been evoked more easily by application of high-potassium containing medium in the presence of cAVA. In vivo, when CSDs were recorded from the frontoparietal cortex, pre-treatment of rats with cAVA (20 mg/kg; i.v.) elevated the mean amplitude of DC potential shifts without altering the number of CSD events compared to vehicle control. Our findings indicate that cAVA, in contrast with vinpocetine, can directly enhance neuronal excitability. This suggests that the memory enhancing effect of vinpocetine may be due to its bioconversion to cAVA. Keywords: Neurophysiology, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Neurophysiology Citation: Farkas B, Kocsis P, Tarnawa I and Tihanyi K (2011). Main Cavinton® metabolite cAVA increases neuronal excitability. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00115 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. B. Farkas, Gedeon Richter Plc.,, Pharmacology and Drug Safety Research, Budapest, Hungary, b.farkas@richter.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers B. Farkas P. Kocsis I. Tarnawa K. Tihanyi Google B. Farkas P. Kocsis I. Tarnawa K. Tihanyi Google Scholar B. Farkas P. Kocsis I. Tarnawa K. Tihanyi PubMed B. Farkas P. Kocsis I. Tarnawa K. Tihanyi Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Palmyrolide A, an unusually stabilized neuroactive macrolide from Palmyra Atoll cyanobacteria.

Palmyrolide A (1) is a new neuroactive macrolide isolated from a marine cyanobacterial assemblage composed of Leptolyngbya cf. and Oscillatoria spp. collected from Palmyra Atoll. It features a rare N-methyl enamide and an intriguing t-butyl branch; the latter renders the adjacent lactone ester bond resistant to hydrolysis. Consistent with its significant suppression of calcium influx in cerebrocortical neurons (IC(50) = 3.70 μM), palmyrolide A (1) showed a relatively potent sodium channel blocking activity in neuro-2a cells (IC(50) = 5.2 μM), without appreciable cytotoxicity.

Hydroxylated Analogs of Mexiletine as Tools for Structural‐Requirements Investigation of the Sodium Channel Blocking Activity

[2-(2-Aminopropoxy)-1,3-phenylene]dimethanol 1 and 4-(2-aminopropoxy)-3-(hydroxymethyl)-5-methylphenol 2, two dihydroxylated analogs of mexiletine - a well known class IB anti-arrhythmic drug - were synthesized and used as pharmacological tools to investigate the blocking-activity requirements of human skeletal muscle, voltage-gated sodium channel. The very low blocking activity shown by newly synthesized compounds corroborates the hypothesis that the presence of a phenolic group in the para-position to the aromatic moiety and/or benzylic hydroxyl groups on the aromatic moiety of local anesthetic-like drugs impairs either the transport to or the interaction with the binding site in the pore of Na(+) channels.

Palmyramide A, a Cyclic Depsipeptide from a Palmyra Atoll Collection of the Marine CyanobacteriumLyngbya majuscula

Bioassay-guided fractionation of the extract of a consortium of a marine cyanobacterium and a red alga (Rhodophyta) led to the discovery of a novel compound, palmyramide A, along with the known compounds curacin D and malyngamide C. The planar structure of palmyramide A was determined by one- and two-dimensional NMR studies and mass spectrometry. Palmyramide A is a cyclic depsipeptide that features an unusual arrangement of three amino acids and three hydroxy acids; one of the hydroxy acids is the rare 2,2-dimethyl-3-hydroxyhexanoic acid unit (Dmhha). The absolute configurations of the six residues were determined by Marfey's analysis, chiral HPLC analysis, and GC/MS analysis of the hydrolysate. Morphological and phylogenetic studies revealed the sample to be composed of a Lyngbya majuscula-Centroceras sp. association. MALDI-imaging analysis of the cultured L. majuscula indicated that it was the true producer of this new depsipeptide. Pure palmyramide A showed sodium channel blocking activity in neuro-2a cells and cytotoxic activity in H-460 human lung carcinoma cells.

Discovery of a novel class of isoxazoline voltage gated sodium channel blockers

Analogs of the previously reported voltage gated sodium channel blocker CDA54 were prepared in which one of the amide functions was replaced with aromatic and non-aromatic heterocycles. Replacement of the amide with an aromatic heterocycle resulted in significant loss of sodium channel blocking activity, while non-aromatic heterocycle replacements were well tolerated.

Synthesis and in vitro sodium channel blocking activity evaluation of novel homochiral mexiletine analogs

New chiral mexiletine analogs were synthesized in their optically active forms and evaluated in vitro as use-dependent blockers of skeletal muscle sodium channels. Tests carried out on sodium currents of single muscle fibers of Rana esculenta demonstrated that all of them exerted a higher use-dependent block than mexiletine. The most potent analog, (S)-3-(2,6-dimethylphenoxy)-1-phenylpropan-1-amine (S)-(5), was six-fold more potent than (R)-Mex in producing a tonic block. As observed with mexiletine, the newly synthesized compounds exhibit modest enantioselective behavior, that is more evident in 3-(2,6-dimethylphenoxy)butan-1-amine (3).