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Concept: Sodium channel blocker

154

One quarter of deaths in Rett Syndrome (RTT), an X-linked neurodevelopmental disorder, are sudden and unexpected. RTT is associated with prolonged QTc interval (LQT), and LQT-associated cardiac arrhythmias are a potential cause of unexpected death. Standard of care for LQT in RTT is treatment with β-adrenergic antagonists; however, recent work indicates that acute treatment of mice with RTT with a β-antagonist, propranolol, did not prevent lethal arrhythmias. In contrast, acute treatment with a sodium channel blocker, phenytoin, prevented arrhythmias. Chronic dosing of propranolol may be required for efficacy; therefore, we tested the efficacy of chronic treatment with either propranolol or phenytoin on RTT mice. Phenytoin completely abolished arrhythmias, whereas propranolol showed no benefit. Surprisingly, phenytoin also normalized weight and activity, but worsened breathing patterns. To explore the role of sodium channel blockers on QT in people with RTT, we performed a retrospective analysis of QT status before and after sodium channel blocker antiepileptic therapies. Individuals with RTT and LQT significantly improved their QT interval status after being started on sodium channel blocker antiepileptic therapies. Thus, sodium channel blockers should be considered for the clinical management of LQT in individuals with RTT.

Concepts: Cardiology, Cardiac arrest, Cardiac electrophysiology, Long QT syndrome, QT interval, Anticonvulsant, Sodium channel blocker, Antiarrhythmic agents

28

The nonselective sodium channel blocker lidocaine is widely used as a local anesthetic but also systemically for treatment of postoperative and neuropathic pain. Voltage-gated sodium channels are crucial for action potential generation and conduction, and their availability controls the amount of activity-dependent conduction velocity slowing. This important axonal property, as assessed by microneurography, is used to differentiate human mechanoinsensitive (silent) nociceptors from the classical polymodal nociceptors. In the current study, microneurography was used to assess axonal properties of the 2 main nociceptor classes in humans, before and after intradermal injection of lidocaine .1% or control saline solution in the receptive field. In mechanosensitive nociceptors, lidocaine reduced baseline conduction velocity and turned activity-dependent slowing into speeding of conduction. In contrast, mechanoinsensitive fibers were not affected in their baseline conduction velocity or their activity-dependent slowing, but probability of conduction block with repetitive stimulation increased. Recovery cycles showed reduced hyperpolarization in all C-fiber classes after lidocaine injections. These results support our hypothesis that sodium channel subtypes are differentially expressed in the 2 nociceptor classes of mechanosensitive C-fibers (CMs) and mechanoinsensitive C-fibers (CMis). PERSPECTIVE: This study reveals that microneurography can be used to assess pharmacological effects on single C-fibers directly in humans.

Concepts: Pharmacology, Neuron, Action potential, Pain, Sodium channel, Sodium channel blocker, Local anesthetic, Lidocaine

3

Trigeminal neuralgia (TN) is a rare severe unilateral facial pain condition. Current guidelines in trigeminal neuralgia management recommend sodium channel blockers – carbamazepine or oxcarbazepine – as the first-line treatment. However, the currently available drugs are often associated with poor tolerability resulting in sub-optimal pain control. CNV1014802 is a novel sodium channel blocker that is being assessed in the treatment of trigeminal neuralgia. Due to the severity of the condition, it is not ethical to conduct a traditional placebo-controlled randomized controlled trial. It is also difficult to use an active control such as carbamazepine, the current gold standard, because of its complex pharmacology and potential for drug interactions.Methods/design: The trial uses a randomized withdrawal design to assess efficacy in this rare condition. There is a 21-day open-label phase followed by a randomized 28-day placebo-controlled phase for responders. Thirty patients will be randomized. The primary outcome measure will be pain relief, but secondary measures of quality of life will be of significant importance given the effect of this condition on activities of daily living. Safety and adverse event endpoints are described.

Concepts: Pharmacology, Randomized controlled trial, Pain, Sodium channel blocker, Gold standard, Carbamazepine, Pain management, Trigeminal neuralgia

0

Hypertrophic cardiomyopathy has a range of clinical severity in children. Treatment options are limited, mainly on account of small patient size. Disopyramide is a sodium channel blocker with negative inotropic properties that effectively reduces left ventricular outflow tract gradients in adults with hypertrophic cardiomyopathy, but its efficacy in children is uncertain. A retrospective chart review of patients ⩽21 years of age with hypertrophic cardiomyopathy at our institution and treated with disopyramide was performed. Left ventricular outflow tract Doppler gradients before and after disopyramide initiation were compared as the primary outcome measure. Nine patients received disopyramide, with a median age of 5.6 years (range 6 days-12.9 years). The median left ventricular outflow tract Doppler gradient before initiation of disopyramide was 81 mmHg (range 30-132 mmHg); eight patients had post-initiation echocardiograms, in which the median lowest recorded Doppler gradient was 43 mmHg (range 15-100 mmHg), for a median % reduction of 58.2% (p=0.002). With median follow-up of 2.5 years, eight of nine patients were still alive, although disopyramide had been discontinued in six of the nine patients. Reasons for discontinuation included septal myomectomy (four patients), heart transplantation (one patient), and side effects (one patient). Disopyramide was effective for the relief of left ventricular outflow tract obstruction in children with hypertrophic cardiomyopathy, although longer-term data suggest that its efficacy is not sustained. In general, it was well tolerated. Further study in larger patient populations is warranted.

Concepts: Cardiomyopathy, Population, Effectiveness, Hypertrophic cardiomyopathy, Sodium channel blocker

0

Lappaconitine (LC) is a natural diterpenoid alkaloid (DTA), acting as a human heart sodium channel blocker and possessing a wide range of biological activities, the cellular and molecular mechanisms of which are widely studied. This interest is due to the fact that various representatives of this DTA class show opposite biological activities. The possible reasons for this difference seem to be related to the peculiarities of the substituent effect on the drug-receptor binding process. In this work, the influence of substituents on the reactivity of LC and its derivatives has been studied by using elementary processes of photodecomposition. The given approach includes the joint analysis of the photophysical properties of the studied systems and their photodecomposition quantum yields. It allows us to trace the influence of substituents, located in the diterpenoid skeleton and anthranilic fragment, on processes in both moieties of LC. Summarizing the data obtained, an inverse dependence of fluorescence and photodegradation quantum yields has been observed. This correlation established for LCs, in particular, allows one to propose a way to evaluate the photostability of potential drugs based on fluorescence analysis. This would be appropriate for compounds in which the reactivity depends on intersystem crossing, i.e. in the cases where the initial and reacting excited states differ in multiplicity.

Concepts: Electron, Molecular biology, Photon, Quantum mechanics, Chemistry, Atom, Sodium channel blocker, Substituent

0

This study aimed to analyze the retention rate of lacosamide (LCM) in patients with epilepsy and intellectual disabilities (IDs), to identify factors influencing retention rate, and to investigate the LCM retention rate with and without concomitant sodium channel blocker (SCB). We hypothesized that the retention rate of LCM with concomitant SCB would be lower than without SCB.

Concepts: Time, Sodium channel blocker

0

Voltage-gated sodium channels (VGSC) are important in the initiation and propagation of action potentials in afferent sensory nerve fibers responsible for evoking cough. This study investigated the efficacy of GSK2339345, a VGSC inhibitor, in the treatment of refractory chronic cough (RCC).

Concepts: Nervous system, Neuron, Action potential, Electrophysiology, Voltage-gated ion channel, Axon, Sodium channel, Sodium channel blocker

0

A consistent line of investigation proposes that fibromyalgia is a sympathetically maintained neuropathic pain syndrome. Dorsal root ganglia sodium channels may play a major role in fibromyalgia pain transmission. Ambroxol is a secretolytic agent used in the treatment of various airway disorders. Recently, it was discovered that this compound is also an efficient sodium channel blocker with potent anti-neuropathic pain properties. We evaluated the add-on effect of ambroxol to the treatment of fibromyalgia. We studied 25 patients with fibromyalgia. Ambroxol was prescribed at the usual clinical dose of 30 mg PO 3 times a day × 1 month. At the beginning and at the end of the study, all participants filled out the Revised Fibromyalgia Impact Questionnaire (FIQ-R) and the 2010 ACR diagnostic criteria including the widespread pain index (WPI). At the end of the study, FIQ-R decreased from a baseline value of 62 ± 15 to 51 ± 19 (p = 0.013). Pain visual analogue scale decreased from 77 ± 14 to 56 ± 30 (p = 0.018). WPI diminished from 14.6 ± 3.1 to 10.4 ± 5.3 (p = 0.001). Side effects were minor. In this pilot study, the use of ambroxol was associated to decreased fibromyalgia pain and improved fibromyalgia symptoms. The open nature of our study does not allow extracting the placebo effect from the positive results. The drug was well tolerated. Ambroxol newly recognized pharmacological properties could theoretically interfere with fibromyalgia pain pathways. Dose escalating-controlled studies seem warranted.

Concepts: Therapeutic effect, Pharmacology, Dorsal root ganglion, Pain, Sodium, Fibromyalgia, Sodium channel blocker, Myofascial pain syndrome

0

The present study examined the role of the dorsolateral striatum (DLS) in extinction behavior. Male Long-Evans rats were initially trained on the straight alley maze, in which they were reinforced to traverse a straight runway and retrieve food reward at the opposite end of the maze. After initial acquisition, animals were given extinction training using 1 of 2 distinct protocols: response extinction or latent extinction. For response extinction, the animal was released from the same starting position and had the opportunity to perform the originally reinforced approach response to the goal end of the maze, which no longer contained food. For latent extinction, the animal was confined to the original goal location without food, allowing the animal to form a new cognitive expectation (i.e., that the goal location is no longer reinforced). Immediately before response or latent extinction training, animals received bilateral intra-DLS administration of the sodium channel blocker bupivacaine or control injections of physiological saline. Results indicated that neural inactivation of the DLS with bupivacaine impaired response extinction, but did not influence latent extinction. The dissociation observed indicates that the DLS selectively mediates extinction mechanisms involving suppression of the original response, as opposed to cognitive mechanisms involving a change in expectation. (PsycINFO Database Record

Concepts: Psychology, Animal, Sodium channel blocker, Extinction, Reinforcement, Saline, Hyponatremia, The Opportunity

0

Saxitoxin (STX) and its analogues are potent voltage-gated sodium channel blockers biosynthesized by freshwater cyanobacteria and marine dinoflagellates. We previously identified genetically predicted biosynthetic intermediates of STX at early stages, Int-A' and Int-C'2, in these microorganisms. However, the mechanism to form the tricyclic skeleton of STX was unknown. To solve this problem, we screened for unidentified intermediates by analyzing the results from previous incorporation experiments with (15) N-labeled Int-C'2. The presence of monohydroxy-Int-C'2 and possibly Int-E' was suggested, and 11-hydroxy-Int-C'2 and Int-E' were identified from synthesized standards and LC-MS. Furthermore, we observed that the hydroxy group at C11 of 11-hydroxy-Int-C'2 was slowly replaced by CD3 O in CD3 OD. Based on this characteristic reactivity, we propose a possible mechanism to form the tricyclic skeleton of STX via a bicyclic intermediate from 11-hydroxy-Int-C'2.

Concepts: Scientific method, Bacteria, Action potential, Voltage-gated ion channel, Sodium, Sodium channel blocker, Dinoflagellate, Saxitoxin