Potassium channel blockers in multiple sclerosis: Neuronal Kv channels and effects of symptomatic treatment

Imbalance of ionic conductances contributes to diverse symptoms of demyelination

Fast axonal conduction of action potentials in mammals relies on myelin insulation. Demyelination can cause slowed, blocked, desynchronized, or paradoxically excessive spiking that underlies the symptoms observed in demyelination diseases. The diversity and timing of such symptoms are poorly understood, often intermittent, and uncorrelated with disease progress. We modeled the effects of demyelination (and secondary remodeling) on intrinsic axonal excitability using Hodgkin-Huxley and reduced Morris-Lecar models. Simulations and analysis suggested a simple explanation for the breadth of symptoms and revealed that the ratio of sodium to leak conductance, g(Na)/g(L), acted as a four-way switch controlling excitability patterns that included spike failure, single spike transmission, afterdischarge, and spontaneous spiking. Failure occurred when this ratio fell below a threshold value. Afterdischarge occurred at g(Na)/g(L) just below the threshold for spontaneous spiking and required a slow inward current that allowed for two stable attractor states, one corresponding to quiescence and the other to repetitive spiking. A neuron prone to afterdischarge could function normally unless it was switched to its "pathological" attractor state; thus, although the underlying pathology may develop slowly by continuous changes in membrane conductances, a discontinuous change in axonal excitability can occur and lead to paroxysmal symptoms. We conclude that tonic and paroxysmal positive symptoms as well as negative symptoms may be a consequence of varying degrees of imbalance between g(Na) and g(L) after demyelination. The KCNK family of g(L) potassium channels may be an important target for new drugs to treat the symptoms of demyelination.

Substituted N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs as potent Kv1.3 ion channel blockers. Part 2

We report the synthesis and in vitro activity of a series of novel substituted N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs. These analogs showed potent inhibitory activity against Kv1.3. Several demonstrated similar potency to the known Kv1.3 inhibitor PAP-1 when tested under the IonWorks patch clamp assay conditions. Two compounds 13i and 13rr were advanced further as potential tool compounds for in vivo validation studies.

N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs as potent Kv1.3 inhibitors. Part 1

We report the synthesis and in vitro activity of a series of novel N-{3-[(1,1-dioxido-1,2-benzothiazol-3-yl)(phenyl)amino]propyl}benzamide analogs. These analogs showed potent inhibitory activity against Kv1.3. Several compounds, including compound 8b, showed similar potency to the known Kv1.3 inhibitor PAP-1 when tested under the IonWorks patch clamp assay conditions.

Dalfampridine extended release: in multiple sclerosis

Dalfampridine extended release (ER) is an orally administered formulation of dalfampridine (fampridine, 4-aminopyridine), a potassium channel antagonist indicated for the improvement in walking ability in patients with multiple sclerosis (MS). Oral dalfampridine ER improved walking ability in patients with MS in three randomized, double-blind trials of up to 15 weeks' duration. In a phase II trial, percentage improvements in walking speed on the Timed 25-Foot Walk (T25FW) test (primary endpoint) were not significant versus baseline or placebo during treatment with dalfampridine ER 10, 15 or 20 mg twice daily. However, according to a post hoc analysis, response rates were significantly higher with dalfampridine ER than placebo, with a consistent mean improvement in walking speed of 25-29% seen in the pooled results from dalfampridine ER responders during the double-blind treatment period. In two phase III trials, the proportion of timed walk responders (primary endpoint) was significantly greater with dalfampridine ER 10 mg twice daily than with placebo, with improvements in walking speed of approximately 25% seen during dalfampridine ER treatment amongst timed walk responders. Interim results of noncomparative extensions of the two phase III trials showed that consistent improvements in walking speed were sustained above baseline for up to 2.5 years of dalfampridine ER treatment. Oral dalfampridine ER 10 mg twice daily was generally well tolerated in patients with MS, according to the results of the three randomized, double-blind, placebo-controlled trials.

Central and peripheral fatigue: exemplified by multiple sclerosis and myasthenia gravis

Fatigue is a feature of several chronic diseases of the central and peripheral nervous system. The pathophysiology of central fatigue is complex and often not well-defined. In contrast, peripheral fatigue is more objectively defined and measured. Fatigue can be part of the primary disease process, but there are often contributions from comorbid factors such as depression, sleep disturbance, medication, or deconditioning. Multiple sclerosis (MS) offers an example of central fatigue. More than 40% of MS patients complain of fatigue. Validated questionnaires are used to assess fatigue severity and comorbid factors. Although fatigue is believed to be a primary process in MS, depression and sleep disturbance are often comorbid problems. Magnetic resonance imaging (MRI), positron emission tomography, and functional MRI studies suggest that fatigue is related to gray matter disease, particularly of the cerebral cortex, but also of the thalamus and caudate. Disruption of impulse propagation from demyelination is also a likely factor. It is uncertain if pro-inflammatory cytokines have a specific effect on the genesis of MS fatigue. Several medications have been reported to alleviate fatigue in MS, but controlled studies show contradictory results. Treatment of depression and sleep disturbance, use of exercise programs and rehabilitation therapies as well as treatment of other comorbid conditions is necessary for optimal alleviation of fatigue. Myasthenia gravis (MG) patients exhibit peripheral fatigue. In contrast to MS, the mechanism of weakness and fatigue in MG is well-defined. Antibodies to the postsynaptic acetylcholine receptor at the myoneural junction cause diminution of the force of muscle contractions. This leads to a feeling of fatigue. MG treatments increase the availability of acetylcholine and reduce antibody formation. Evaluation for comorbid conditions, especially thymoma and hyperthyroidism, are mandatory in patients with MG.

Dalfampridine for the treatment of ambulatory impairment in multiple sclerosis

Dalfampridine is a potassium-channel blocker that is approved by the US FDA as 10 mg extended-release tablets to improve walking in patients with multiple sclerosis. Approval is currently pending in Europe. This is the first pharmacological symptomatic treatment approved for multiple sclerosis patients of any type with walking difficulties. Relative to an immediate-release formulation, the extended-release formulation of dalfampridine lowers peak serum concentrations that contribute to toxicity while maintaining a comparable amount of total drug exposure. Several studies show the efficacy and tolerability of dalfampridine. The pivotal published clinical trial demonstrated a treatment–responder rate of 35% compared with an 8% placebo–responder rate (p < 0.0001). The subjects who responded to treatment had an average improvement in their 25-foot walking test time of 25.2% (95% CI: 21.5–28.8) compared with an average improvement of 4.7% (95% CI: 1.0–8.4) in subjects who responded to placebo. Seizures are the most serious adverse effect of dalfampridine with a probable dose-dependent likelihood of occurrence.

Bis(4-amino-pyridinium) sulfate monohydrate

The asymmetric unit of the title compound, 2C₅H₇N₂⁺·SO₄²⁻·H₂O, contains two 4-amino­pyridinium cations (A and B), a sulfate dianion and a water mol­ecule. One of the 4-amino­pyridinium cations (B) is disordered over two orientations with refined site occupancies of 0.568 (4) and 0.432 (4). The non-H atoms of the 4-amino­pyridinium cations are essentially coplanar, with a maximum deviation of 0.055 (1) Å (in cation A), 0.022 (3) Å (for the major component in cation B) and 0.009 (3) Å (for the minor component in cation B). In the crystal, the sulfate O atoms link the 4-amino­pyridinium cations and water mol­ecules into a three-dimensional network via inter­molecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. The crystal structure is further consolidated by N—H⋯O(water) and C—H⋯O(water) hydrogen bonds.

Thermoregulation in multiple sclerosis

Multiple sclerosis (MS) is a progressive neurological disorder that disrupts axonal myelin in the central nervous system. Demyelination produces alterations in saltatory conduction, slowed conduction velocity, and a predisposition to conduction block. An estimated 60-80% of MS patients experience temporary worsening of clinical signs and neurological symptoms with heat exposure. Additionally, MS may produce impaired neural control of autonomic and endocrine functions. This review focuses on five main themes regarding the current understanding of thermoregulatory dysfunction in MS: 1) heat sensitivity; 2) central regulation of body temperature; 3) thermoregulatory effector responses; 4) heat-induced fatigue; and 5) countermeasures to improve or maintain function during thermal stress. Heat sensitivity in MS is related to the detrimental effects of increased temperature on action potential propagation in demyelinated axons, resulting in conduction slowing and/or block, which can be quantitatively characterized using precise measurements of ocular movements. MS lesions can also occur in areas of the brain responsible for the control and regulation of body temperature and thermoregulatory effector responses, resulting in impaired neural control of sudomotor pathways or neural-induced changes in eccrine sweat glands, as evidenced by observations of reduced sweating responses in MS patients. Fatigue during thermal stress is common in MS and results in decreased motor function and increased symptomatology likely due to impairments in central conduction. Although not comprehensive, some evidence exists concerning treatments (cooling, precooling, and pharmacological) for the MS patient to preserve function and decrease symptom worsening during heat stress.

KCa channels as therapeutic targets in episodic ataxia type-2

Episodic ataxia type-2 (EA2) is an inherited movement disorder caused by mutations in the gene encoding the Ca(v)2.1alpha1 subunit of the P/Q-type voltage-gated calcium channel that result in an overall reduction in the P/Q-type calcium current. A consequence of these mutations is loss of precision of pacemaking in cerebellar Purkinje cells. This diminished precision reduces the information encoded by Purkinje cells and is thought to contribute to symptoms associated with this disorder. The loss of the precision of pacemaking in EA2 is the consequence of reduced activation of calcium-dependent potassium channels (K(Ca)) by the smaller calcium current and in vitro can be pharmacologically restored by K(Ca) activators. We used a well established mouse model of EA2, the tottering (tg/tg) mouse, to examine the potential therapeutic utility of one such Food and Drug Administration (FDA)-approved compound, chlorzoxazone (CHZ). Compared with wild-type Purkinje cells, we found the firing rate of tg/tg Purkinje cells in acutely prepared cerebellar slices to be very irregular. Bath application of CHZ successfully restored the precision of pacemaking in a dose-dependent manner. Oral administration of CHZ to tg/tg mice improved their baseline motor performance and reduced the severity, frequency, and duration of episodes of dyskinesia without producing any adverse effects. We propose the use of CHZ, which is currently FDA approved as a muscle relaxant, as a safe and novel treatment of EA2.

The therapeutic mode of action of 4-aminopyridine in cerebellar ataxia

Episodic ataxia type 2 (EA2) is a hereditary cerebellar ataxia associated with mutations in the P/Q-type voltage-gated calcium (Ca(2+)) channels. Therapeutic approaches for treatment of EA2 are very limited. Presently, the potassium (K(+)) channel blocker 4-aminopyridine (4-AP) constitutes the most promising treatment, although its mechanism of action is not understood. Here we show that, in contrast to what is commonly believed, therapeutic concentrations of 4-AP do not increase the inhibitory drive of cerebellar Purkinje cells. Instead, 4-AP restores the severely diminished precision of pacemaking in Purkinje cells of EA2 mutant mice by prolonging the action potential and increasing the action potential afterhyperpolarization. Consistent with this mode of action, the therapeutic efficacy of 4-AP was comparable, and not additive, to chlorzoxazone, an activator of Ca(2+)-dependent K(+) channels that also restores the precision of Purkinje cell pacemaking. The likely target of 4-AP at the concentrations used are the K(v)1 family of K(+) channels, possibly the K(v)1.5 subtype. Because at higher concentrations 4-AP blocks a large array of K(+) channels and is a proconvulsant, use of selective K(v)1 channel blockers is likely to be a safer substitute for treatment of cerebellar ataxia.

Effect of 4-Aminopyridine on Action Potential Parameters in Isolated Dog Purkinje Fibers

Introduction

4-Aminopyridine (fampridine), a potassium channel blocker, has demonstrated efficacy in improving lower extremity strength and walking speed in patients with multiple sclerosis. Since in vitro electrophysiologic studies are recommended for evaluating a drug's potential to prolong the QT interval and induce such cardiac arrhythmias as Torsades de Pointes, we examined the electrophysiologic effects of 4-aminopyridine (0.5, 5.0, 50, and 500 µM) on isolated canine Purkinje fibers.

Methods

Microelectrodes monitored the resting membrane potential, overshoot, amplitude of action potential (AP), and maximal rate of depolarization of the AP upstroke in Purkinje fibers stimulated at 0.5 and 1.0 Hz.

Results

None of the above variables were altered in the presence of 4-aminopyridine. The AP duration at 30%, 50%, and 90% repolarization was also monitored, with only the 500-µM concentration at the 1.0-Hz frequency significantly increasing these values with respect to baseline (P < 0.05). However, the small sample size (N = 4) was small. The proportional increases, and their 95% confidence intervals, were 90.8% (−36.4%, 218.0%), 25.8% (11.9%, 39.7%), and 22.0% (14.9%, 29.1%) for APD 30%, 50%, and 90% repolarization, respectively. Reverse rate dependence was not observed, suggesting inhibition of ion channels other than those contributing to QT interval prolongation.

Assessment of the cardiac safety of fampridine-SR sustained-release tablets in a thorough QT/QTc evaluation at therapeutic and supratherapeutic doses in healthy individuals

OBJECTIVE

To characterize the effects of a sustained-release formulation of fampridine (fampridine-SR) on QT interval in healthy subjects.

METHODS

In a double-blind, double-dummy trial, healthy subjects were randomized to 5 days treatment with fampridine-SR at therapeutic (10 mg twice daily) or supratherapeutic (30 mg twice daily) doses, placebo or moxifloxacin (400 mg on treatment day 5). Digital 12-lead electrocardiograms were recorded before treatment and on day 5; blood samples determined fampridine concentrations. Central tendency analysis determined whether the upper limit of the CI for the QT (individual-corrected QT; QTcI) interval change exceeded 10 ms. Outlier analysis determined new-onset QT (corrected QT; QTc) intervals; maximum change in QTc from baseline of 30 - 60 ms and maximum change from baseline >or= 60 ms. The relationship between pharmacokinetic parameters and QTcI values is explored.

RESULTS

Moxifloxacin was associated with a QTcI interval increase > 5 ms at 7 time points; no increase was observed with either dose of fampridine-SR; there were no fampridine outliers. Pharmacokinetic evaluation failed to find dose-dependent cardiac effects. Fampridine was well tolerated, with a higher frequency of adverse events at the supratherapeutic dose.

CONCLUSION

This study showed that fampridine-SR at therapeutic and supratherapeutic doses was not associated with QT prolongation in healthy subjects.

Steady-state pharmacokinetics and tolerability of orally administered fampridine sustained-release 10-mg tablets in patients with multiple sclerosis: a 2-week, open-label, follow-up study

BACKGROUND

Fampridine sustained release (SR) has generally been well tolerated in clinical studies in patients with multiple sclerosis (MS) at doses < or = 20 mg/d. The pharmacokinetics of single escalating doses of fampridine SR (5, 10, 15, and 20 mg) were evaluated in a companion study.

OBJECTIVES

The primary objective of this study, which followed on from the single-dose pharmacokinetic study, was to assess the steady-state pharmacokinetics of fampridine in patients with MS over 2 weeks of oral administration of open-label fampridine SR 20 mg BID. Tolerability was also evaluated.

METHODS

The dose of fampridine SR was titrated upward to twice-daily administration over days 1 and 2, with 20 mg given in the morning and 10 mg in the evening. From days 3 to 14, patients received fampridine SR 20 mg BID (total daily dose, 40 mg). Fampridine pharmacokinetic parameters were determined on days 1, 8, and 15. The parameters of interest included C(max), T(max), C(min), AUC, and apparent t((1/2)) These parameters were compared with those from the single-dose study. Tolerability was assessed based on adverse events, physical examinations, vital signs, laboratory tests, and ECGs.

RESULTS

Twenty-one white patients who participated in the single-dose study were enrolled in the steady-state study (52.4% female; mean [SD] age, 45.1 [7.4] years; weight range, 54-87 kg). Fampridine pharmacokinetic parameters on day 1 were consistent with those obtained in the single-dose study. The T(max) did not differ significantly between day 1, day 8, day 15, and the single-dose study (range, 3.25-3.78 hours). C(max) values on days 8 and 15 (66.7 and 62.6 ng/mL, respectively) were significantly higher than those on day 1 (48.6 ng/mL) and in the single-dose study (50.5 ng/mL) (all, P < 0.001), reflecting accumulation of fampridine with multiple dosing. Values for C(max)/C(min) did not differ significantly between day 1 and the single-dose study (2.44 and 2.43, respectively) or between days 8 and 15 (2.90 and 2.88, respectively); however, the single-dose and day-1 values differed significantly from the day-8 and day-15 values (P < or = 0.001). There were no significant differences with respect to any other pharmacokinetic parameters. One hundred adverse events were reported by 21 patients. With the exception of 1 case of severe nausea, all adverse events were of mild to moderate severity. Thirty-five events reported by 14 subjects were considered treatment related. Dizziness was the most common treatment-related adverse event, with 11 episodes reported by 8 patients. No clinically significant changes were found in clinical laboratory values, vital signs, or physical examination findings from baseline to the last visit, and there were no clinically significant changes in QTc intervals (Bazett's correction).

CONCLUSIONS

In these patients with MS, the steady-state pharmacokinetic profile of fampridine SR 20 mg BID administered for 2 weeks appeared to support the use of twice-daily dosing in this population. This dosage was generally well tolerated.

Pharmacokinetics and tolerability of single escalating doses of fampridine sustained-release tablets in patients with multiple sclerosis: a Phase I-II, open-label trial

BACKGROUND

Fampridine (4-aminopyridine) is a potassium channel-blocking agent that has been reported to have therapeutic potential for improving walking and mobility in patients with multiple sclerosis (MS). A sustained-release (SR) formulation of fampridine was developed to improve the agent's pharmacokinetic profile by extending its t((1/2)) relative to that of immediate-release fampridine.

OBJECTIVES

The primary study objective was to examine the pharmacokinetics of fampridine SR tablets after single escalating doses in patients with MS. Tolerability was evaluated as a secondary end point.

METHODS

This multicenter, Phase I-II, open-label trial evaluated the dose proportionality and tolerability of 4 single doses of fampridine SR (5, 10, 15, and 20 mg) in patients with MS. There was a 4-day washout between doses. Blood samples were collected immediately before drug administration, hourly for the first 8 hours after administration, and at 10, 12, 14, 18, and 24 hours after administration. The pharmacokinetic parameters evaluated included C(max), T(max), AUC, elimination rate constant, apparent elimination t((1/2)), and apparent CL/F. Twelve-lead ECGs were obtained at baseline (0.5 hour before dosing) and at 1, 4, 12, and 24 hours after drug administration to evaluate potential effects on the QTc interval. All adverse events, abnormal laboratory values, and ECG abnormalities were recorded and evaluated for clinical relevance. Adverse-event data were monitored for 24 hours after the last dose, and patients were instructed to report any adverse events for 14 days after the conclusion of the study.

RESULTS

Twenty-four white patients were enrolled (58% female; mean [SD] age, 45.4 [7.3] years; weight range, 47.8-87.1 kg), and 23 completed the study. Mean plasma concentrations and AUC values were dose proportional. T(max) occurred at 3.36 to 3.92 hours after dosing; the apparent elimination t((1/2)) was 5.47 hours. Both sex and weight affected the pharmacokinetic parameters of fampridine SR. Eleven treament-related adverse events were reported in 10 patients, with dizziness being the most common (7 incidents reported by 6 patients [1 at 10 mg, 3 at 15 mg, and 3 at 20 mg]). Other adverse events included amblyopia, asthenia, headache, and ataxia. All treatment-related adverse events were mild to moderate in severity, with the exception of 1 case of dizziness (20 mg) that was considered severe. No serious adverse events were reported, and no clinically significant changes in corrected QT intervals were observed. No patients with-drew due to treatment-related adverse events.

CONCLUSION

In these patients with MS, fampridine SR (5-20 mg) had a potentially advantageous pharmacokinetic profile relative to that associated with immediate-release fampridine and was generally well tolerated.

Fatigue in multiple sclerosis: mechanisms and management

Multiple sclerosis [MS] is a chronic immune-mediated disorder of the central nervous system [CNS]. Fatigue may be a debilitating symptom in MS patients, adversely impacting on their quality of life. Clinically, fatigue may manifest as exhaustion, lack of energy, increased somnolence, or worsening of MS symptoms. Activity and heat typically serve to exacerbate symptoms of fatigue. There is now strong evidence to suggest that fatigue results from reduced voluntary activation of muscles by means of central mechanisms. Given that axonal demyelination is a pathological hallmark of MS, activity-dependent conduction block [ADCB] has been proposed as a mechanism underlying fatigue in MS. This ADCB results from axonal membrane hyperpolarization, mediated by the Na(+)/K(+) electrogenic pump, with conduction failure precipitated in demyelinated axons with a reduced safety factor of impulse transmission. In addition, Na(+)/K(+) pump dysfunction, as reported in MS, may induce a depolarizing conduction block associated with inactivation of Na(+) channels. These processes may induce secondary effects including axonal degeneration triggered by raised levels of intracellular Ca(2+) through reverse operation of the Na(+)-Ca(2+) exchanger. Restoration of normal conduction in demyelinated axons with selective channel blockers improves fatigue and may yet prove useful as a neuroprotective strategy, in preventing secondary axonal degeneration and consequent functional impairment.

Involvement of the 4-aminopyridine-sensitive transient A-type K+ current in macrophage-induced neuronal injury

Through their capacity to secrete, upon activation, a variety of bioactive molecules, brain macrophages (and resident microglia) play an important role in brain immune and inflammatory responses. To test our hypothesis that activated macrophages induce neuronal injury by enhancing neuronal outward K(+) current, we studied the effects of lipopolysaccharide (LPS)-stimulated human monocyte-derived macrophage (MDM) on neuronal transient A-type K(+) current (I(A)) and resultant neuronal injury in primary rat hippocampal neuronal cultures. Bath application of LPS-stimulated MDM-conditioned media (MCM+) enhanced neuronal I(A) in a concentration-dependent manner. Non-stimulated MCM (MCM-) failed to alter I(A). The enhancement of neuronal I(A) was recapitulated in neurons co-cultured with macrophages. The link of MCM(+)-induced enhancement of I(A) to MCM(+)-associated neuronal injury, as detected by propidium iodide and 4'',6-diamidino-2-phenylindol staining (DAPI) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, was demonstrated by experimental results showing that addition of I(A) blocker 4-aminopyridine to the cultures protected hippocampal neurons from MCM(+)-induced neuronal injury. Further investigation revealed that glutamate was involved in MCM(+)-induced enhancement of neuronal I(A). These results suggest that during brain inflammation macrophages (and microglia) might mediate neuronal injury via enhancement of neuronal I(A), and that neuronal K(v) channel might be a potential target for the development of therapeutic strategies for some neurodegenerative disorders by which immune and inflammatory responses are believed to be involved in the pathogenesis.

3,4-diaminopyridine safety in clinical practice: an observational, retrospective cohort study

Fatigue is one of the most common and disabling symptoms of multiple sclerosis (MS) and has a significant, often underestimated, impact on patients' quality of life. Current management is mainly symptomatic. 3,4-diaminopyridine (3,4-DAP) is a voltage-dependent potassium channel blocker that has been used on a named patient basis in Europe for many years to improve motor function and fatigue in patients with MS and other neuromuscular disorders, and it is undergoing the European approval process for Lambert-Eaton myasthenic syndrome (LEMS). The efficacy and safety of 3,4-DAP as symptomatic therapy in MS have not been widely evaluated. This study aimed to assess the safety profile of 3,4-DAP in routine clinical practice in an observational, retrospective study. The study involved 669 patients of the Rennes Multiple Sclerosis Clinic, France, who were treated with 3,4-DAP for the relief of fatigue during the period 1998-2003. Overall, 18.2% of patients presented adverse drug reactions (ADRs) while using moderate doses of 3,4-DAP (20-30 mg daily or up to 80 mg daily for patients with LEMS) for periods of up to 51 months. The majority of ADRs were mild to moderate and transient or reversible at the end of treatment (mean treatment duration = two months) or after dose adjustment. Most did not require discontinuation. The most commonly observed ADRs were paraesthesias. There was one case of epileptic seizure, one of hepatotoxicity and one of heart palpitations thought 'possibly' to be linked to 3,4-DAP. These underline the need for continued monitoring during treatment with 3,4-DAP.

Dependence of 6beta-acetoxy-7alpha-hydroxyroyleanone block of Kv1.2 channels on C-type inactivation

Voltage-gated K(+) (Kv) channels exhibit slow or C-type inactivation during continuous depolarization. A selective pharmacological agent targeting C-type inactivation is hitherto lacking. Here, we report that 6beta-acetoxy-7alpha-hydroxyroyleanone (AHR), a diterpenoid compound isolated from Taiwania cryptomerioides, can selectively modify C-type inactivation of Kv1.2 channels. Extracellular, but not intracellular, AHR (50 muM) dramatically accelerated the slow decay of Kv currents and left-shifted the steady-state inactivation curve. AHR blocked Kv currents with an IC(50) of 17.7 muM. AHR did not affect the kinetics and voltage-dependence of Kv1.2 channel activation. Channel block by AHR was independent of intracellular K(+) concentration. In addition, effect of AHR was much attenuated in a Kv1.2 V370G mutant defective in C-type inactivation. Therefore, block of Kv1.2 channels by AHR did not appear to involve direct occlusion of the outer pore but depended on C-type inactivation. AHR could thus be a probe targeting Kv channel C-type inactivation gate.

Alternative splicing and transcriptome profiling of experimental autoimmune encephalomyelitis using genome-wide exon arrays

Background

Multiple Sclerosis (MS) is a chronic inflammatory disease causing demyelination and nerve loss in the central nervous system. Experimental autoimmune encephalomyelitis (EAE) is an animal model of MS that is widely used to investigate complex pathogenic mechanisms. Transcriptional control through isoform selection and mRNA levels determines pathway activation and ultimately susceptibility to disease.

Methodology/Principal Findings

We have studied the role of alternative splicing and differential expression in lymph node cells from EAE-susceptible Dark Agouti (DA) and EAE-resistant Piebald Virol Glaxo.AV1 (PVG) inbred rat strains using Affymetrix Gene Chip Rat Exon 1.0 ST Arrays. Comparing the two strains, we identified 11 differentially spliced and 206 differentially expressed genes at day 7 post-immunization, as well as 9 differentially spliced and 144 differentially expressed genes upon autoantigen re-stimulation. Functional clustering and pathway analysis implicate genes for glycosylation, lymphocyte activation, potassium channel activity and cellular differentiation in EAE susceptibility.

Conclusions/Significance

Our results demonstrate that alternative splicing occurs during complex disease and may govern EAE susceptibility. Additionally, transcriptome analysis not only identified previously defined EAE pathways regulating the immune system, but also novel mechanisms. Furthermore, several identified genes overlap known quantitative trait loci, providing novel causative candidate targets governing EAE.

Aminopyridines potentiate synaptic and neuromuscular transmission by targeting the voltage-activated calcium channel beta subunit

Aminopyridines such as 4-aminopyridine (4-AP) are widely used as voltage-activated K(+) (Kv) channel blockers and can improve neuromuscular function in patients with spinal cord injury, myasthenia gravis, or multiple sclerosis. Here, we present novel evidence that 4-AP and several of its analogs directly stimulate high voltage-activated Ca(2+) channels (HVACCs) in acutely dissociated neurons. 4-AP, 4-(aminomethyl)pyridine, 4-(methylamino)pyridine, and 4-di(methylamino)pyridine profoundly increased HVACC, but not T-type, currents in dissociated neurons from the rat dorsal root ganglion, superior cervical ganglion, and hippocampus. The widely used Kv channel blockers, including tetraethylammonium, alpha-dendrotoxin, phrixotoxin-2, and BDS-I, did not mimic or alter the effect of 4-AP on HVACCs. In HEK293 cells expressing various combinations of N-type (Cav2.2) channel subunits, 4-AP potentiated Ca(2+) currents primarily through the intracellular beta(3) subunit. In contrast, 4-AP had no effect on Cav3.2 channels expressed in HEK293 cells. Furthermore, blocking Kv channels did not mimic or change the potentiating effects of 4-AP on neurotransmitter release from sensory and motor nerve terminals. Thus, our findings challenge the conventional view that 4-AP facilitates synaptic and neuromuscular transmission by blocking Kv channels. Aminopyridines can directly target presynaptic HVACCs to potentiate neurotransmitter release independent of Kv channels.

Lack of kainic acid-induced gamma oscillations predicts subsequent CA1 excitotoxic cell death

Gamma oscillations are a prominent feature of hippocampal network activity, but their functional role remains debated, ranging from mere epiphenomena to being crucial for information processing. Similarly, persistent gamma oscillations sometimes appear prior to epileptic discharges in patients with mesial temporal sclerosis. However, the significance of this activity in hippocampal excitotoxicity is unclear. We assessed the relationship between kainic acid (KA)-induced gamma oscillations and excitotoxicity in genetically engineered mice in which N-methyl-D-aspartic acid receptor deletion was confined to CA3 pyramidal cells. Mutants showed reduced CA3 pyramidal cell firing and augmented sharp wave-ripple activity, resulting in higher susceptibility to KA-induced seizures, and leading to strikingly selective neurodegeneration in the CA1 subfield. Interestingly, the increase in KA-induced gamma-aminobutyric acid (GABA) levels, and the persistent 30-50-Hz gamma oscillations, both of which were observed in control mice prior to the first seizure discharge, were abolished in the mutants. Consequently, on subsequent days, mutants manifested prolonged epileptiform activity and massive neurodegeneration of CA1 cells, including local GABAergic neurons. Remarkably, pretreatment with the potassium channel blocker alpha-dendrotoxin increased GABA levels, restored gamma oscillations, and prevented CA1 degeneration in the mutants. These results demonstrate that the emergence of low-frequency gamma oscillations predicts increased resistance to KA-induced excitotoxicity, raising the possibility that gamma oscillations may have potential prognostic value in the treatment of epilepsy.

Axonal ion channels from bench to bedside: a translational neuroscience perspective

Over recent decades, the development of specialised techniques such as patch clamping and site-directed mutagenesis have established the contribution of neuronal ion channel dysfunction to the pathophysiology of common neurological conditions including epilepsy, multiple sclerosis, spinal cord injury, peripheral neuropathy, episodic ataxia, amyotrophic lateral sclerosis and neuropathic pain. Recently, these insights from in vitro studies have been translated into the clinical realm. In keeping with this progress, novel clinical axonal excitability techniques have been developed to provide information related to the activity of a variety of ion channels, energy-dependent pumps and ion exchange processes activated during impulse conduction in peripheral axons. These non-invasive techniques have been extensively applied to the study of the biophysical properties of human peripheral nerves in vivo and have provided important insights into axonal ion channel function in health and disease. This review will provide a translational perspective, focusing on an overview of the investigational method, the clinical utility in assessing the biophysical basis of ectopic symptom generation in peripheral nerve disease and a review of the major findings of excitability studies in acquired and inherited neurological disease states.

Patents related to therapeutic activation of K(ATP) and K(2P) potassium channels for neuroprotection: ischemic/hypoxic/anoxic injury and general anesthetics

BACKGROUND

Mechanisms of neuroprotection encompass energy deficits in brain arising from insufficient oxygen and glucose levels following respiratory failure; ischemia or stroke, which produce metabolic stresses that lead to unconsciousness and seizures; and the effects of general anesthetics. Foremost among those K(+) channels viewed as important for neuroprotection are ATP-sensitive (K(ATP)) channels, which belong to the family of inwardly rectifying K(+) channels (K(ir)) and contain a sulfonylurea subunit (SUR1 or SUR2) combined with either K(ir)6.1 (KCNJ8) or K(ir)6.2 (KCNJ11) channel pore-forming alpha-subunits, and various members of the tandem two-pore or background (K(2P)) K(+) channel family, including K(2P)1.1 (KCNK1 or TWIK1), K(2P)2.1 (KCNK2 or TREK/TREK1), K(2P)3.1 (KCNK3 or TASK), K(2P)4.1 (KCNK4 or TRAAK), and K(2P)10.1 (KCNK10 or TREK2).

OBJECTIVES

This review covers patents and patent applications related to inventions of therapeutics, compound screening methods and diagnostics, including K(ATP) channel openers and blockers, as well as K(ATP) and K(2P) nucleic/amino acid sequences and proteins, vectors, transformed cells and transgenic animals. Although the focus of this patent review is on brain and neuroprotection, patents covering inventions of K(ATP) channel openers for cardioprotection, diabetes mellitus and obesity, where relevant, are addressed.

RESULTS/CONCLUSIONS

Overall, an important emerging therapeutic mechanism underlying neuroprotection is activation/opening of K(ATP) and K(2P) channels. To this end substantial progress has been made in identifying and patenting agents that target K(ATP) channels. However, current K(2P) channels patents encompass compound screening and diagnostics methodologies, reflecting an earlier 'discovery' stage (target identification/validation) than K(ATP) in the drug development pipeline; this reveals a wide-open field for the discovery and development of K(2P)-targeting compounds.

Angiotensin II increases excitability and inhibits a transient potassium current in vagal primary sensory neurons

The octapeptide angiotensin II (ANG II) plays a pivotal role in the maintenance of blood pressure by activating ANG II receptors located in variety of cell types including neurons housed in the central nervous system (CNS) and in the peripheral nervous system (PNS). ANG II (100 nM) blocked spike frequency accommodation (SFA) recorded with whole-cell patch technique in acutely isolated nodose ganglion neurons (NGN) from adult rats. ANG II increased the frequency of action potentials (AP) produced by supramaximal 500 ms depolarizing currents recorded in both tonic (16 Hz vs. 58 Hz, control vs. ANG II perfusion respectively, n=9) and phasic (1Hz vs. 38 Hz, n=13) NGNs. ANG II produced no significant changes in: the resting membrane potential (-51 mV vs. -50 mV, n=65), AP overshoot (46 mV vs. 41 mV, n=25), AP undershoot (-65 mV vs. -61 mV, n=25), AP duration (1 ms vs. 1.2 ms, n=25), and AP threshold (-40 mV vs. -43 mV, n=19). CV-11974 (600 nM), a specific AT1 receptor antagonist, prevented ANG II-evoked changes SFA (n=10). ANG II (100 nM) had no significant effect on total outward potassium current (I(K)) but inhibited a fast activating and fast inactivating I(K) recorded in the presence of TEA. A kinetically similar I(K) was also inhibited by 4-AP (3mM). In phasic NGNs, 4-AP occluded the effects of 100 nM ANG II on SFA. Our results indicate that ANG II can block an A-type of I(K) and that this effect may underlie the ANG II-mediated change in SFA.

Bis(4-amino-pyridinium) tetra-chlorido-cobaltate(II)

In the title compound, (C₅H₇N₂)₂[CoCl₄], the cobalt(II) ion is coordinated by four chloride ions in a slightly distorted tetra­hedral geometry. The crystal packing is stabilized by inter­molecular N—H⋯Cl hydrogen bonding, forming a three-dimensional network. The crystal was a non-merohedral twin emulating tetra­gonal symmetry, but being in fact ortho­rhom­bic.

Bis(4-amino-pyridinium) bis(hydrogen oxalate) monohydrate

In the title compound, 2C₅H₇N₂⁺·2C₂HO₄⁻·H₂O, the asymmetric unit consists of an amino­pyridinium cation, an oxalic actetate anion and a half-molecule of water, which lies on a two-fold rotation axis. The crystal packing is consolidated by inter­molecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. The mol­ecules are linked into an infinite one dimensional chain along [010].

4-Amino-pyridinium hydrogen succinate

In the title salt, C₅H₇N₂⁺·C₄H₅O₄⁻, the asymmetric unit comprises an amino­pyridinium cation and a hydrogen succinate anion as protonation of the aromatic N atom of the 4-amino­pyridine mol­ecule has occurred. The crystal packing is stabilized by inter­molecular O—H⋯O and N—H⋯O hydrogen bonds that lead to a two-dimensional array. Short C—H⋯O contacts are also present.

Sustained-release oral fampridine in multiple sclerosis: a randomised, double-blind, controlled trial

BACKGROUND

Clinical studies suggested that fampridine (4-aminopyridine) improves motor function in people with multiple sclerosis. This phase III study assessed efficacy and safety of oral, sustained-release fampridine in people with ambulatory deficits due to multiple sclerosis.

METHODS

We undertook a randomised, multicentre, double-blind, controlled phase III trial. We randomly assigned 301 patients with any type of multiple sclerosis to 14 weeks of treatment with either fampridine (10 mg twice daily; n=229) or placebo (n=72), using a computer-generated sequence stratified by centre. We used consistent improvement on timed 25-foot walk to define response, with proportion of timed walk responders in each treatment group as the primary outcome. We used the 12-item multiple sclerosis walking scale to validate the clinical significance of the response criterion. Efficacy analyses were based on a modified intention-to-treat population (n=296), which included all patients with any post-treatment efficacy data. The study is registered with ClinicalTrials.gov, number NCT00127530.

FINDINGS

The proportion of timed walk responders was higher in the fampridine group (78/224 or 35%) than in the placebo group (6/72 or 8%; p<0.0001). Improvement in walking speed in fampridine-treated timed walk responders, which was maintained throughout the treatment period, was 25.2% (95% CI 21.5% to 28.8%) and 4.7% (1.0% to 8.4%) in the placebo group. Timed walk responders showed greater improvement in 12-item multiple sclerosis walking scale scores (-6.84, 95% CI -9.65 to -4.02) than timed walk non-responders (0.05, -1.48 to 1.57; p=0.0002). Safety data were consistent with previous studies.

INTERPRETATION

Fampridine improved walking ability in some people with multiple sclerosis. This improvement was associated with a reduction of patients' reported ambulatory disability, and is a clinically meaningful therapeutic benefit.

N-(4-pyridyl) methyl carbamate inhibits fast potassium currents in guinea pig dorsal root ganglion cells

Axonal demyelination is a critical pathological phenomenon associated with spinal cord injury and multiple sclerosis (MS). Previous studies demonstrated that 4-Aminopyridine, a fast potassium channel blocker, enhances impulse conduction on damaged and/or demyelinated axons, allowing for functional recovery in spinal cord injuries and MS, but with severe therapeutic limitations. To continue to explore the therapeutic value of blocking fast potassium channels while circumventing the side effects of 4-AP, we have developed three novel 4-AP derivatives that enhance impulse conduction in spinal cord trauma. In the current study, we have shown that one of these three derivatives, N-(4-pyridyl) methyl carbamates (MC), significantly inhibits a fast, I(A) like potassium current in guinea pig dorsal root ganglion cells in a whole cell patch clamp configuration. This inhibition of I(A) likely plays a critical role in MC's ability to restore conduction in mechanically injured spinal cord axons and may present a viable alternative to 4-AP for individuals with spinal cord injury or MS. From this, compounds with greater efficacy and perhaps less side effects will likely emerge in the near future, which will greatly enhance the functional restoration and lessen the suffering of SCI and MS patients.

Octa-akis(4-amino-pyridine)-1κN,2κN-aqua-2κO-μ-carbonato-1:2κO,O':O''-dinickel(II) dichloride penta-hydrate

In the title compound, [Ni(2)(CO(3))(C(5)H(6)N(2))(8)(H(2)O)]Cl(2)·5H(2)O, one of the the Ni(II) ions is six-coordinated in a distorted octa-hedral geometry, with the equatorial plane defined by four pyridine N atoms from four amino-pyridine ligands, the axial positions being occupied by one water O and a carbonate O atom. The other Ni(II) ion is also six-coordinated, by four other pyridine N atoms from four other amino-pyridine ligands and two carbonate O atoms to complete a distorted octa-hedral geometry. In the crystal structure, mol-ecules are linked into an infinite three-dimensional network by O-H⋯O, N-H⋯Cl, N-H⋯O, O-H⋯N, C-H⋯O, C-H⋯N and C/N-H⋯π inter-actions involving the pyridine rings.

Sustained-release fampridine for symptomatic treatment of multiple sclerosis

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical trials, and adverse effects of sustained-release (SR) fampridine in patients with multiple sclerosis (MS).

DATA SOURCES

An English-language human data search was done using PubMed/MEDLINE (1966-August 2008) to retrieve relevant material using the search terms fampridine-SR, 4-aminopyridine, and multiple sclerosis. References of selected articles and information from the drug developer were used to further identify pertinent trials.

STUDY SELECTION AND DATA EXTRACTION

Article selection was based primarily on studies that evaluated the pharmacokinetics, safety, and efficacy of fampridine-SR in patients with MS. Relevant meeting abstracts were also included as part of the analysis.

DATA SYNTHESIS

Fampridine-SR is a sustained-release, orally administered potassium-channel blocker acting in the central nervous system to enhance conduction in demyelinated axons. Several small trials have evaluated the safety and efficacy of fampridine-SR in patients with MS to improve their walking ability. Data from a recent large Phase 3 trial indicated that walking speed improved in 42.9% of patients with MS who were treated with fampridine-SR compared with 9.3% of those who received placebo (p < 0.001). Treatment-related adverse events associated with the use of fampridine-SR include dizziness, insomnia, nausea, and paresthesia. More severe adverse events, such as seizure, have occurred in patients receiving doses higher than those currently recommended.

CONCLUSIONS

Positive results from 2 Phase 3 clinical trials have put fampridine-SR on the path toward approval as a medication for improving walking speed and lower extremity strength in patients with MS.

4-Amino-pyridinium 4-nitro-benzoate 4-nitro-benzoic acid

The asymmetric unit of the title compound, C(5)H(7)N(2) (+)·C(7)H(4)NO(4) (-)·C(7)H(5)NO(4), consists of an amino-pyridinium cation, a 4-nitro-benzoate anion and a neutral 4-nitro-benzoic acid mol-ecule. The pyridine ring forms dihedral angles of 64.70 (5)° and 70.37 (5)°, respectively, with the benzene rings of 4-nitro-benzoic acid and 4-nitro-benzoate. In the crystal structure, the cations, anions and the neutral 4-nitro-benzoic acid mol-ecules are linked by O-H⋯O and N-H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). Adjacent networks are cross-linked via C-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distances 3.6339 (6) and 3.6566 (6) Å].

The Kv channel blocker 4-aminopyridine enhances Ag+ uptake: a scanning electrochemical microscopy study of single living cells

We report that silver ion (Ag(+)) uptake is enhanced by 4-aminopyridine (4-AP), a well known voltage-sensitive potassium ion channel (K(v)) blocker. Both bacterial (Escherichia coli) and mammalian (3T3 fibroblast) cells were used as model systems. Ag(+) uptake was monitored with a scanning electrochemical microscope with an amperometric Ag(+) ion-selective electrode (Ag(+)-ISE) and the respiration rates of E. coli cells were measured by oxygen reduction at an ultramicroelectrode. The results showed that not only the amount but also the rate of silver uptake by the cells increased significantly when 4-AP was added to the solution. For fibroblasts, the Ag(+) uptake rate was 4.8 x 10(7) ions per cell per sec without 4-AP compared with 1.0 x 10(8) ions per cell per sec with 0.2 mM 4-AP. For E. coli cells, the uptake rate was 1.5 x 10(4) ions per cell per sec without 4-AP vs. 3.5 x 10(4) ions per cell per sec with 0.5 mM 4-AP and 5.9 x 10(4) ions per cell per sec with 1 mM 4-AP. Thus, 4-AP might be useful where silver is used as antimicrobial agent to speed its uptake.

Up-regulation of slow K(+) channels in peripheral motor axons: a transcriptional channelopathy in multiple sclerosis

Spinal lesions produce plastic changes in motoneuron properties. We have documented the excitability of motor axons in the median nerve of 12 patients with multiple sclerosis and 50 normal subjects, hypothesizing that plastic changes in the properties of spinal motoneurons might be reflected in the properties of peripheral motor axons and be demonstrable in vivo. In the patients, there were changes in physiological measures of axonal excitability attributable to increased slow K(+) channel activity. Other measures were within control limits. These changes could be modelled by an 11% increase in slow K(+) current, with compensatory changes in membrane potential, suggesting increased expression of the responsible channels. The changes cannot be explained solely by changes in membrane potential and are not those expected if peripheral nerve axons were involved in the inflammatory process of multiple sclerosis. They probably represent a transcriptional channelopathy, due to up-regulation of channel expression. The abnormalities do not imply that peripheral nerve function has been significantly compromised, but they do suggest that the properties of the parent motoneurons have changed. This study thus provides evidence for plasticity in motoneuronal properties at a molecular level, the first such evidence for intact human subjects.

Tetra-kis(4-amino-pyridine-κN)dichlorido-copper(II) monohydrate

The asymmetric unit of the title compound, [CuCl(2)(C(5)H(6)N(2))(4)]·H(2)O, contains two crystallographically independent complex mol-ecules and two water mol-ecules. The Cu(II) ion in each mol-ecule is six-coordinated in an elongated octa-hedral geometry, with the equatorial plane defined by four pyridine N atoms of four amino-pyridine ligands and the axial positions occupied by two Cl atoms. In the crystal structure, mol-ecules are linked into a three-dimensional framework by C-H⋯Cl, O-H⋯Cl, N-H⋯O, N-H⋯Cl and N-H⋯N hydrogen bonds and C/N-H⋯π inter-actions involving the pyridine rings.

4-Amino-pyridinium 4-amino-benzene-sulfonate 4-ammonio-benzene-sulfonate monohydrate

The asymmetric unit of the title compound, C₅H₇N₂⁺·C₆H₆NO₃S⁻·C₆H₇NO₃S·H₂O, contains one 4-ammonio­benzene­sulfonate zwitterion (⁺H₃NC₆H₄SO₃⁻), one 4-amino­benzene­sulfonate anion (H₂NC₆H₄SO₃⁻), one 4-amino­pyridinium cation and two half-mol­ecules of water, each lying on a twofold rotation axis. The various ions and molecules in the structure are linked through N—H⋯O, N—H⋯N and N—H⋯S hydrogen bonds and C—H—π inter­actions into a three-dimensional framework.

Drugs and their molecular targets: an updated overview

About 330 targets bind approved drugs, 270 encoded by the human genome and 60 belonging to pathogenic organisms. A large number of druggable targets have been recently proposed from preclinical and first clinical data, but a huge reservoir of putative drug targets, possibly several thousands, remains to be explored. This overview considers the different types of ligands and their selectivity in the main superfamilies of drug targets, enzymes, membrane transporters and ion channels, and the various classes of membrane and nuclear receptors with their signalling pathway. Recently approved drugs such as monoclonal antibodies, tyrosine kinase and proteasome inhibitors, and major drugs under clinical studies are reviewed with their molecular target and therapeutic interest. The druggability of emerging targets is discussed, such as multidrug resistance transporters and cystic fibrosis transmembrane conductance regulator (CFTR), hyperpolarization-activated cyclic nucleotides-gated (HCN), cyclic nucleotide-gated (CNG) and transient receptor potential (TRP) ion channels, tumour necrosis factor (TNF) and receptor activator of NFkappaB (RANK) receptors, integrins, and orphan or recently deorphanized G-protein-coupled and nuclear receptors. Large advances have been made in the therapeutical use of recombinant cytokines and growth factors (i.e. tasonermin, TNFalpha-1a; becaplermin, platelet-derived growth factor (PDGF); dibotermin-alpha, bone morphogenetic proteins (BMP)2; anakinra, interleukin-1 receptor antagonist protein (IRAP), and in enzyme replacement therapy, i.e. algasidase (alpha-galactosidase) and laronidase (alpha-l-iduronidase). New receptor classes are emerging, e.g. membrane aminopeptidases, and novel concepts are stimulating drug research, e.g. epigenetic therapy, but the molecular target of some approved drugs, such as paracetamol and imidazolines, still need to be identified.

Gambierol, a toxin produced by the dinoflagellate Gambierdiscus toxicus, is a potent blocker of voltage-gated potassium channels

In this study, we pharmacologically characterized gambierol, a marine polycyclic ether toxin which is produced by the dinoflagellate Gambierdiscus toxicus. Besides several other polycyclic ether toxins like ciguatoxins, this scarcely studied toxin is one of the compounds that may be responsible for ciguatera fish poisoning (CFP). Unfortunately, the biological target(s) that underlies CFP is still partly unknown. Today, ciguatoxins are described to specifically activate voltage-gated sodium channels by interacting with their receptor site 5. But some dispute about the role of gambierol in the CFP story shows up: some describe voltage-gated sodium channels as the target, while others pinpoint voltage-gated potassium channels as targets. Since gambierol was never tested on isolated ion channels before, it was subjected in this work to extensive screening on a panel of 17 ion channels: nine cloned voltage-gated ion channels (mammalian Na(v)1.1-Na(v)1.8 and insect Para) and eight cloned voltage-gated potassium channels (mammalian K(v)1.1-K(v)1.6, hERG and insect ShakerIR) expressed in Xenopus laevis oocytes using two-electrode voltage-clamp technique. All tested sodium channel subtypes are insensitive to gambierol concentrations up to 10 microM. In contrast, K(v)1.2 is the most sensitive voltage-gated potassium channel subtype with almost full block (>97%) and an half maximal inhibitory concentration (IC(50)) of 34.5 nM. To the best of our knowledge, this is the first study where the selectivity of gambierol is tested on isolated voltage-gated ion channels. Therefore, these results lead to a better understanding of gambierol and its possible role in CFP and they may also be useful in the development of more effective treatments.

Carbon monoxide-releasing molecule tricarbonyldichlororuthenium (II) dimer induces concentration-dependent alterations in the electrophysiological properties of axons in mammalian spinal cord

Traumatic spinal cord injury (SCI) typically involves intraparenchymal hemorrhage and a cascade of inflammatory and cytotoxic processes leading to tissue necrosis and apoptosis. A consequence of the hemorrhage is the accumulation of deoxygenated heme proximal and distal to the epicenter of the lesion. The heme oxygenase (HO) system is an endogenous heme degradation system and is upregulated following neurotrauma. The breakdown of heme via HO activity yields the byproducts carbon monoxide (CO), biliverdin, and iron. CO has documented neuromodulatory properties; however, the effects of elevated concentrations of CO on axonal conduction in the spinal cord have not previously been studied. The present study tested the hypothesis that CO causes alterations in the electrophysiological properties of axons within the isolated guinea-pig spinal cord. Ex vivo spinal cord preparations were exposed to 100, 500, and 1000 microM concentrations of the carbon monoxide-releasing molecule (CORM) 2 for 30 min in a double sucrose gap electrophysiological recording system and the compound action potential (CAP) and membrane potential (CMP) were recorded continuously during pretreatment, CORM-2 treatment, and washout (30 min) with Krebs' solution. CAP amplitude and area were significantly (P<0.05) reduced following treatment with 500 and 1000 microM CORM-2 and did not recover during washout. No effect on CMP was observed, however, stimulus-peak latency did increase significantly (P<0.05) following CORM-2 treatment at these concentrations, and a decrease in the amplitude of the second CAP elicited by paired-pulse stimulation was also evident at interpulse intervals of 2 and 4 ms. These results are consistent with a CO-induced alteration in axonal conduction, possibly attributable to modified Na+ channel conductance. They also identify a new mechanism by which post-traumatic hemorrhage contributes to the neurological deficits observed following SCI.

Intrinsic excitability of cholinergic neurons in the rat parabigeminal nucleus

Cholinergic neurons in the parabigeminal nucleus of the rat midbrain were studied in an acute slice preparation. Spontaneous, regular action potentials were observed both with cell-attached patch recordings as well as with whole cell current-clamp recordings. The spontaneous activity of parabigeminal nucleus (PBN) neurons was not due to synaptic input as it persisted in the presence of the pan-ionotropic excitatory neurotransmitter receptor blocker, kynurenic acid, and the cholinergic blockers dihydro-beta-erythroidine (DHbetaE) and atropine. This result suggests the existence of intrinsic currents that enable spontaneous activity. In voltage-clamp recordings, I(H) and I(A) currents were observed in most PBN neurons. I(A) had voltage-dependent features that would permit it to contribute to spontaneous firing. In contrast, I(H) was significantly activated at membrane potentials lower than the trough of the spike afterhyperpolarization, suggesting that I(H) does not contribute to spontaneous firing of PBN neurons. Consistent with this interpretation, application of 25 microM ZD-7288, which blocked I(H), did not affect the rate of spontaneous firing in PBN neurons. Counterparts to I(A) and I(H) were observed in current-clamp recordings: I(A) was reflected as a slow voltage ramp observed between action potentials and on release from hyperpolarization, and I(H) was reflected as a depolarizing sag often accompanied by rebound spikes in response to hyperpolarizing current injections. In response to depolarizing current injections, PBN neurons fired at high frequencies, with relatively little accommodation. Ultimately, the spontaneous activity in PBN neurons could be used to modulate cholinergic drive in the superior colliculus in either positive or negative directions.

Fampridine-SR for multiple sclerosis and spinal cord injury

Fampridine-SR is a sustained-release tablet form of the K(+) channel-blocking compound 4-aminopyridine that has been shown to restore conduction in focally demyelinated axons, to enhance synaptic transmission in many types of neurons and to potentiate muscle contraction. The present review describes the mechanism of action and chemistry of Fampridine-SR, its pharmacokinetics and safety, and the outcomes of clinical trials of its safety and efficacy for enhancing neuromuscular function in patients with multiple sclerosis or spinal cord injury. Randomized clinical trials completed to date indicate that this form of K(+) channel blockade may be useful for the improvement of walking ability in patients with multiple sclerosis.

Venom therapy in multiple sclerosis

To date many people with multiple sclerosis (MS) seek complementary and alternative medicines (CAM) to treat their symptoms as an adjunct to conventionally used therapies. Among the common CAM therapies, there is a renewed interest in the therapeutic potential of venoms in MS. The efficacy of this therapeutic method remains unclear. However, venom-based therapy using bee, snakes and scorpions venom and/or sea anemones toxin has been recently developed because current investigations have identified the various components and molecular mechanism of the effects of venoms under in vitro and in vivo conditions. The aim of this review is to describe the recent findings regarding the role of venoms and their components in treatment of MS disease and that whether venom therapy could be recommended as a complementary treatment or not.

Voltage-gated potassium channel modulation of neurotoxic activity in human immunodeficiency virus type-1(HIV-1)-infected macrophages

Macrophages play an important role in brain immune and inflammatory responses. They are also critical cells in mediating the pathology of neurodegenerative disorders such as HIV-associated dementia. This is largely through their capacity to secrete a variety of bioactive molecules such as cytokines, leading to neuronal dysfunction and/or death. Accumulating evidence indicates that voltage-gated potassium (Kv) channels play a pivotal role in the modulation of macrophage proliferation, activation, and secretion. Blockade of Kv channels by specific antagonists decreases macrophage cytokine production and ameliorates macrophage-associated neuronal injury. These results suggest that Kv channels might become a potential target for the development of new therapeutic strategies for chronic inflammatory diseases.