Quantitative assessment of sustained-release 4-aminopyridine for symptomatic treatment of multiple sclerosis

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].

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.

Evaluation of the six-minute walk in multiple sclerosis subjects and healthy controls

Objective To assess the characteristics of the 6-min walk (6MW) in multiple sclerosis (MS) subjects of varied disability, and controls. To assess the correlation of 6MW to subjective measures of fatigue, health status and ambulation using the modified fatigue impact scale (MFIS), short form-36 Health Questionnaire physical component score and MS walking scale (MSWS).

Methods Forty MS expanded disability status scale [(EDSS) 0—6.5] and 20 control subjects were recruited from a MS outpatient clinic. Subjects completed survey material and three 6MWs with 1-h interval rest in a single study visit.

Results There was no practice effect or fatigability with repeat 6MW tests with a one-h rest period between test sessions. The 6MW had excellent intra-[intraclass correlation coefficient (ICC) = 0.95] and inter-rater (ICC = 0.91) reliability. MS subjects demonstrated reduced 6MW distance and speed compared with controls ( P < 0.0001). Within the MS population 6MW distance was significantly reduced with increasing disability ( P = 0.05). Compared with the EDSS, the 6MW had a stronger correlation to subjective measures of ambulation and physical fatigue: MSWS ( r = -0.81 versus 0.69) and MFISphy (0.66 versus 0.63).

Conclusions The 6MW is a feasible, reproducible, and reliable measure in MS. MS subjects demonstrate motor fatigue in both 6MW distance and speed compared with controls. In MS subjects there is an inverse relationship between motor fatigue and disability. 6MW has a strong correlation to subjective measures of ambulation and physical fatigue. Multiple Sclerosis 2008; 14: 383—390. http://msj.sagepub.com

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.

Possible mechanisms of the formation of chronic fatigue syndrome in the clinical picture of multiple sclerosis

A frequent manifestation of multiple sclerosis (MS) is chronic fatigue syndrome, which can be defined as a subjective decrease in the level of physical and/or mental energy. Chronic fatigue syndrome can be divided into asthenia (fatigue at rest), pathological fatigability (fatigue on physical loading), and fatigue on the background of deterioration of other symptoms (exacerbation of MS). There are both central and peripheral mechanisms for the formation of fatigue. The combination of fatigue and affective disturbances, especially depression and sleep disorders (insomnia, restless legs syndrome) is common in MS and may provide evidence that they share common mechanisms--decreases in the activity of the serotoninergic and noradrenergic systems. An important component in the formation of chronic fatigue syndrome consists of endocrine and autoimmune factors, the latter having a greater effect on asthenia than on pathological fatigue. Further studies of the pathogenetic mechanisms of the formation of asthenia and pathological fatigue and clarification of their differential diagnostic signs should allow not only a better understanding of the nature of this syndrome, but also better selection of individual treatment.

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.

Spinal cord injury medicine. 5. Long-term medical issues and health maintenance

This self-directed learning module highlights long-term care issues in patients with spinal cord injury (SCI). It is part of the study guide on SCI in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. The most common secondary medical complications include pressure ulcers, pneumonia, and genitourinary issues. Health care maintenance is important to prevent medical complications, for general health as well as for issues specific to SCI. Women with SCI have gender-specific issues regarding amenorrhea, sexuality, fertility, and menopause. Options exist to assist disabled men with sexuality and fertility complications. Pain is a common complication after SCI. Many new areas of research in the field of SCI are discussed.

OVERALL ARTICLE OBJECTIVE

To discuss long-term care issues in patients with spinal cord injury, including health maintenance, secondary conditions, women's health, sexual function, pain, and spinal cord regeneration and recovery.

Molecular docking study of the binding of aminopyridines within the K+ channel

We present a molecular docking study aimed to identify the binding site of protonated aminopyridines for the blocking of voltage dependent K(+) channels. Several active aminopyridines are considered: 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 3,4-diaminopyridine, and 4-aminoquinoleine. We apply the AutoDock force field with a lamarckian genetic algorithm, using atomic charges for the ligands derived from the electrostatic potential obtained at the B3LYP/cc-pVDZ level. We find a zone in the alpha-subunit of the K(+) channel bearing common binding sites. This zone corresponds to five amino acids comprised between residuals Thr107 and Ala111, in the KcsA K(+) channel (1J95 pdb structure). The 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, and 3,4-diaminopyridine bind to the carboxylic oxygens of Thr107 and Ala111. In all cases aminopyridines are perpendicular to the axis of the pore. 4-aminoquinoleine binds to the carboxylic oxygen of Ala111. Due to its large size, the molecular plane is parallel to the axis of the pore. The charge distributions and the structures of the binding complexes suggest that the interaction is driven by formation of several hydrogen bonds. We find 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, and 3,4-diaminopyridine with similar binding energy. Considering the standard error of the estimate of the AutoDock force field, this energy should lie, as a rough estimation, in the interval 3-7 kcal mol(-1). On the other hand, 4-aminoquinoleine seems to have a smaller binding energy.

Fampridine-SR in multiple sclerosis: a randomized, double-blind, placebo-controlled, dose-ranging study

Objective To determine the safety of sustained-release 4-aminopyridine in subjects with mutiple sclerosis (MS) and to examine dose-related efficacy up to 40 mg twice daily.

Method Multicenter, randomized, double-blind, placebo-controlled, study. Following a 4-week baseline peroid, subjects were randomly assigned to receive Fampridine-SR (n=25, doses from 10 to 40 mg twice daily, increasing in 5 mg increments weekly) or placebo (n=11). A battery of assessments was performed weekly, including the MS Functional Composite (MSFC), fatigue questionnaires, and lower extremity manual muscle testing.

Results The most common adverse events were dizziness, insomnia, paresthesia, asthenia, nausea, headache, and tremor. Five subjects were discontinued from Fampridine-SR because of adverse events at doses greater than 25 mg, and these included convulsions in two subjects at doses of 30 and 35 mg twice daily. Improvement were seen in lower extremity muscle strength (prospective analysis) and walking speed (post-hoc analysis) in the Fampridine-SR group compared to placebo (unadjusted p-values of 0.01 and 0.03, respectively). There were no significant differences in other MSFC measure or fatigue scores.

Conclusions Future studies should employ doses up to 20 mg twice daily with lower extremity strength and walking speed as potential outcome measures. Multiple Sclerosis 2007; 13: 357-368. http://msj.sagepub.com

An efficient and chemoselective synthesis of N-substituted 2-aminopyridines via a microwave-assisted multicomponent reaction

A facile and selective synthesis of N-substituted 2-aminopyridines is accomplished via microwave-assisted multi-component reactions controlled by the basicity of amine and the nature of solvent. In addition, a possible mechanism accounting for the reaction was proposed.

Clinical impact of 20% worsening on Timed 25-foot Walk and 9-hole Peg Test in multiple sclerosis

INTRODUCTION

Quantitative tests of motor function, like the Timed 25-foot Walk (T25FW) and 9-hole Peg Test (9HPT), are increasingly being applied as outcome measures in multiple sclerosis (MS) clinical trials. The quantitative nature of the data has a favorable impact on responsiveness, but the clinical impact of the changes is uncertain. The goal of this study was to assess whether a change on T25FW and 9HPT does indeed have a clinical meaning. This was accomplished by comparing 20% changes on these quantitative measurements to concomitant changes on the Guy's Neurological Disability Scale (GNDS), a scale which measures patient-perceived daily life disability.

METHODS

From a longitudinal database, we selected patients with at least two measurements of T25FW, 9HPT and GNDS with a minimal time interval of 350 days. In those patients who experienced at least a 20% change on T25FW or 9HPT, GNDS score changes were examined more closely.

RESULTS

Of 527 patients, 143 experienced a >20% worsening on their T25FW and 71 on their 9HPT, respectively. Patients with a 20% increase in T25FW or 9HPT had more GNDS worsening than patients without such an increase. GNDS worsening associated with an increase in T25FW was mainly due to an increase in perceived disability related to lower extremity function and fatigue; GNDS worsening associated with an increase in 9HPT was more diffuse with respect to domains involved.

CONCLUSION

Worsening on T25FW or 9HPT has a clinical impact on disability, as perceived by MS patients during daily life functioning.

Theoretical prediction of relative and absolute pKa values of aminopyridines

This work presents a study aimed at the theoretical prediction of pK(a) values of aminopyridines, as a factor responsible for the activity of these compounds as blockers of the voltage-dependent K(+) channels. To cover a large range of pK(a) values, a total of seven substituted pyridines is considered as a calibration set: pyridine, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2-chloropyridine, 3-chloropyridine, and 4-methylpirydine. Using ab initio G1, G2 and G3 extrapolation methods, and the CPCM variant of the Polarizable Continuum Model for solvation, we calculate gas phase and solvation free energies. pK(a) values are obtained from these data using a thermodynamic cycle for describing protonation in aqueous and gas phases. The results show that the relatively inexpensive G1 level of theory is the most accurate at predicting pK(a) values in aminopyridines. The highest standard deviation with respect to the experimental data is 0.69 pK(a) units for absolute values calculations. The difference increases slightly to 0.74 pK(a) units when the pK(a) is computed relative to the pyridine molecule. Considering only compounds at least as basic as pyridine (the values of interest for bioactive aminopyridines) the error falls to 0.10 and 0.12 pK(a) units for the absolute and relative computations, respectively. The technique can be used to predict the effect of electronegative substituents in the pK(a) of 4-AP, the most active aminopyridine considered in this work. Thus, 2-chloro and 3-chloro-4-aminopyridine are taken into account. The results show a decrease of the pK(a), suggesting that these compounds are less active than 4-AP at blocking the K(+) channel.

Effects of 4-aminopyridine on classical conditioning of the rabbit (Oryctolagus cuniculus) nictitating membrane response

A large body of data suggests that potassium channels may play an important role in learning and memory. Previous in-vitro research in a number of species including Hermissenda and the rabbit suggests that a 4-aminopyridine-sensitive transient potassium channel may be involved in classical conditioning. We investigated the effects of in-vivo 4-aminopyridine administration (0.5 mg/kg) on classical conditioning of the rabbit nictitating membrane response using a battery of tests designed to assess the associative, sensory, and motor contributors of 4-aminopyridine to responding. 4-Aminopyridine enhanced both classical conditioning and conditioning-specific reflex modification compared with a saline vehicle control, and these effects had several nonassociative components including an increase in the frequency of responding to both the conditioned and the unconditioned stimuli, suggesting a sensitizing effect of the drug. Although 4-aminopyridine can have peripheral effects, it may also modify cerebellar excitability or hippocampal neurotransmitter balance resulting in heightened responsiveness to stimulation.

Symptomatic treatment of multiple sclerosis. Multiple Sclerosis Therapy Consensus Group (MSTCG) of the German Multiple Sclerosis Society

Besides immunomodulation and immunosuppression, the specific treatment of symptoms is an essential component of the overall management of multiple sclerosis (MS). Symptomatic treatment is aimed at the elimination or reduction of symptoms impairing the functional abilities and quality of life of the affected patients. Moreover, with symptomatic treatment the development of a secondary physical impairment due to an existing one may be avoided. Many therapeutic techniques as well as different drugs are used for the treatment of MS symptoms, but only a few of them have been investigated, especially in MS patients, and are approved by the national health authorities. Despite an overwhelming number of publications, only a few evidence-based studies exist and consensus reports are very rare, too. Therefore, it seemed necessary to develop a consensus statement on symptomatic treatment of MS comprising existing evidence-based literature as well as therapeutic experience of neurologists who have dealt with these problems over a long time. This consensus paper contains proposals for the treatment of the most common MS symptoms: disorders of motor function and coordination, of cranial nerve function, of autonomic, cognitive, and psychological functions as well as MS-related pain syndromes and epileptic seizures.

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

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) characterized by demyelination, with a relative sparing of axons. In MS patients, many neurologic signs and symptoms have been attributed to the underlying conduction deficits. The idea that neurologic function might be improved if conduction could be restored in CNS demyelinated axons led to the testing of potassium (K(+)) channel blockers as a symptomatic treatment. To date, only 2 broad-spectrum K(+) channel blockers, 4-aminopyridine (4-AP) and 3,4-diaminopyridine (3,4-DAP), have been tested in MS patients. Although both 4-AP and 3,4-DAP produce clear neurologic benefits, their use has been limited by toxicity. Here we review the current status of basic science and clinical research related to the therapeutic targeting of voltage-gated K(+) channels (K(v)) in MS. By bringing together 3 distinct but interrelated disciplines, we aim to provide perspective on a vast body of work highlighting the lengthy and ongoing process entailed in translating fundamental K(v) channel knowledge into new clinical treatments for patients with MS and other demyelinating diseases. Covered are (1) K(v) channel nomenclature, structure, function, and pharmacology; (2) classic and current experimental morphology and neurophysiology studies of demyelination and conduction deficits; and (3) a comprehensive overview of clinical trials utilizing 4-AP and 3,4-DAP in MS patients.

Lewis acid-promoted transformation of 2-alkoxypyridines into 2-aminopyridines and their antibacterial activity. Part 2: Remarkably facile C–N bond formation

2-Alkoxy-3-cyano-4,6-diarylpyridines 1a,b which were synthesized by condensation of alpha,beta-unsaturated ketones with malononitrils were subjected to Lewis acid-catalyzed nucleophilic displacement reaction with various amines to afford the corresponding 2-aminopyridines 3-21. The potency of the results as antibacterial agents has been evaluated. The structure of the newly prepared compounds was assessed by microanalysis, IR, and NMR spectra. Molecular modeling and QSAR methods are used to study the antibacterial activity of the active compounds by means of the molecular mechanic method.

Pharmacokinetics and safety of multiple oral doses of sustained-release 4-aminopyridine (fampridine-sr) in subjects with chronic, incomplete spinal cord injury 11A commercial party with a direct financial interest in the results of the research supporting this article has conferred or will confer a financial benefit on the author or 1 or more of the authors

OBJECTIVE

To examine the pharmacokinetics and safety of sustained-release 4-aminopyridine (Fampridine-SR), a potassium channel blocker, in subjects with chronic, incomplete spinal cord injury (SCI).

DESIGN

Open-label.

SETTING

Clinical research unit in Ontario.

PARTICIPANTS

Sixteen neurologically stable subjects with chronic, incomplete SCI (American Spinal Injury Association Impairment Scale grade B, C, or D).

INTERVENTION

Oral administration of Fampridine-SR (25, 30, 35, 40, 50, 60 mg twice daily, each for 1 wk).

MAIN OUTCOME MEASURES

Steady-state pharmacokinetic parameters: maximum observed plasma concentration (Cmax), minimum observed plasma concentration (Cmin), average observed plasma concentration (Cav), area under the plasma concentration-time curve from 0 to 12 hours (AUC(0-12)), time to Cmax (tmax), plasma half-life (t(1/2)), apparent volume of distribution (Vd/F), and apparent total clearance (Cl/F). Safety assessments: physical examinations, vital sign measurements, clinical laboratory tests, electrocardiogram recordings, and adverse events.

RESULTS

Mean steady-state Cmax, Cmin, Cav, and AUC(0-12) increased over the entire Fampridine-SR dosage range and were dosage dependent up to 50 mg twice daily. Fampridine-SR had a mean tmax of 2.2 to 3.0 hours and a mean t(1/2) of 5.7 to 6.9 hours. Mean Vd/F (415.4-528.0 L) and Cl/F (51.4-57.7 L/h) were independent of dosage, as were mean tmax and t(1/2) across dosages. Adverse events were mild or moderate and were not dosage related. During the entire study period (17 wk), dizziness was the most frequently reported adverse event, followed by urinary tract infection, paresthesia, ataxia, and insomnia.

CONCLUSION

In subjects with chronic, incomplete SCI, Fampridine-SR was slowly absorbed and eliminated, which will allow Fampridine-SR to be administered in a convenient twice-daily manner. Fampridine-SR was well tolerated at dosages from 25 to 60 mg twice daily.

The use of 4-aminopyridine (fampridine) in demyelinating disorders

4-Aminopyridine (4-AP or fampridine) is a potassium channel-blocking agent that has been shown to restore conduction in focally demyelinated axons. A sustained-release matrix tablet form of 4-AP (fampridine-SR) is currently undergoing multicenter clinical trials in patients with multiple sclerosis or chronic spinal cord injury. This review describes the pharmacology and mechanisms of action of 4-AP, its pharmacokinetics in human subjects, and the outcomes of clinical trials employing either immediate-release or sustained-release formulations of the drug. The randomized clinical trials that have been completed to date indicate that K+ channel blockade may prove to be a useful strategy for ameliorating central conduction deficits due to demyelination. Diverse neurological gains have been reported for both motor and sensory domains. At the present time, however, the clinical trials have not provided sufficiently robust or definitive evidence of efficacy to gain regulatory approval for the symptomatic management of patients with either multiple sclerosis or spinal cord injury.

Aminoborohydrides 15. The First Mild and Efficient Method for Generating 2-(Dialkylamino)-pyridines from 2-Fluoropyridine

[reaction: see text] Lithium aminoborohydride (LAB) reagents promote the amination of 2-fluoropyridine under mild reaction conditions, providing 2-(dialkylamino)pyridines in excellent yield and purity. Treatment of 2-fluoropyridine with 1.1 equiv of lithium aminoborohydride at room temperature affords complete conversion after 1 h. This is the first general way by which 2-(dialkylamino)pyridines may be directly obtained from fluoropyridines under ambient reaction conditions. 2-Chloropyridine can also be converted to 2-(dialkylamino)pyridine by simply increasing the number of LAB equivalents and the reaction temperature.

Protein kinase C inhibits the transplasma membrane influx of Ca2+ triggered by 4-aminopyridine in Jurkat T lymphocytes

4-aminopyridine (4AP) is a general blocker of voltage-dependent K+ channels. This pyridine derivative has also been shown to inhibit T cell proliferation, to modulate immune responses and to alleviate some of the symptoms associated with neurological disorders such as multiple sclerosis, myasthenia gravis and Alzheimer's disease. 4AP triggers a Ca2+ response in lymphocytes, astrocytes, neurons and muscle cells but little is known about the regulation of the 4AP response in these cells. We report that 4AP induced a non-capacitative transplasma membrane influx of Ca2+ in Jurkat T lymphocytes. The influx of Ca2+ was not affected by activation or inhibition of protein kinase A (PKA). In contrast, activation of protein kinase C (PKC) by phorbol myristyl acetate (PMA), mezerein or 1-oleoyl-2-acetyl-sn-glycerol (OAG) inhibited the influx of Ca2+ triggered by 4AP. The inhibitory effect of PKC could be prevented by prior exposure of the cells to the PKC inhibitor GF 109203X. Under these conditions, mezerein and OAG no longer inhibited the 4AP-dependent Ca2+ response. Inhibition of serine and threonine protein phosphatases PP1 and PP2A by treating the cells with calyculin A (CalA) reduced the Ca2+ response to 4AP. Okadaic acid (OA) had no effect, suggesting an involvement of PP1. A combination of CalA and OAG (or PMA) abolished the influx of Ca2+ induced by 4AP, adding further evidence to the importance of protein phosphorylation in the modulation of the 4AP response. Our data suggest that the transplasma membrane influx of Ca2+ triggered by 4AP in Jurkat T cells can be modulated by the opposite actions of PKC and protein serine and threonine phosphatase(s).

Pharmacokinetic studies of single and multiple oral doses of fampridine-SR (sustained-release 4-aminopyridine) in patients with chronic spinal cord injury

Fampridine (4-aminopyridine) is a potassium channel blocking agent that restores conduction in demyelinated axons and improves neurologic function in patients with chronic spinal cord injury (SCI). Based on the pharmacokinetic profile of orally administered fampridine, multiple daily doses (4 or more) would need to be taken to sustain its therapeutic effects. Two studies were conducted to determine the pharmacokinetics and safety profile of an oral, sustained-release (SR) formulation of fampridine (fampridine-SR, 10-25 mg) administered as a single dose (n = 14) and twice daily for 1 week (n = 16) in patients with chronic, incomplete SCI. Mean plasma concentrations and area under the plasma concentration-time curve were proportional to the dose administered, whereas other pharmacokinetic parameters were independent of dose. Fampridine-SR was absorbed slowly (peak plasma concentration shortly after dosing, 2.6-3.7 hours) and eliminated (plasma half-life, 5.6-7.6 hours), and reached steady state after 4 days of twice-daily administration. Fampridine-SR was well tolerated, with only mild to moderate adverse events reported, and no serious adverse events. The extended plasma half-life of fampridine-SR allows convenient twice-daily dosing. Clinical trials designed to assess neurologic and functional improvement using fampridine-SR in patients with chronic SCI are currently underway.

Rational modelling of the voltage-dependent K+ channel inactivation by aminopyridines

A functional model for the in vitro inactivation of voltage-dependent K(+) channels is developed. The model expresses the activity as a function of the aminopyridine pK(a), the interaction energy with the receptor, and a quotient of partition functions. Molecular quantum similarity theory is introduced in the model to express the activity as a function of the principal components of the similarity matrix for a series of agonists. To validate the model, a set of five active (protonated) aminopyridines is considered: 2-aminopyridine, 3-aminopyridine, 4-aminoquinoleine, 4-aminopyridine, and 3,4-diaminopyridine. A regression analysis of the model gives good results for the variation of the observed activity with the overlap similarity index when pyridinic rings are superposed. The results support the validity of the model, and the hypothesis of a ligand-receptor entropy variation depending mainly on the nature of the ligand. In addition, the results suggest that the pyridinic ring must play an active role in the interaction with the receptor site. This interaction with the protonated pyridinic nitrogen can involve a cation-pi interaction or a donor hydrogen bond. The amine groups, at different relative positions of the pyridinic nitrogen, can form one or more hydrogen bonds due to the C(4) symmetry of the inner part of the pore in the K(+) channel.

Pharmacokinetics of an immediate-release oral formulation of Fampridine (4-aminopyridine) in normal subjects and patients with spinal cord injury

Plasma concentration profiles of the K+ channel-blocking compound Fampridine were obtained from (1) control subjects (n = 6) following oral administration of doses of 10, 15, 20, and 25 mg and (2) patients with spinal cord injury (SCI) (n = 11) following a single oral dose of 10 mg of an immediate-release formulation. Plasma concentrations were determined using a reversed-phase ion-pair high-performance liquid chromatography (HPLC) assay with ultraviolet light detection employing liquid extraction. The drug was rapidly absorbed with a tmax approximately 1 hour for both groups; tmax was independent of dose. Cmax and AUC0-infinity were linearly related to dose, and t 1/2 was 3 to 4 hours for both groups. There were no obvious differences in the (10-mg) plasma concentration profiles between control subjects and SCI patients. The drug was well tolerated, with only mild and transient side effects of light-headedness, dysesthesias, and dizziness.

Quantitative functional measures in MS: what is a reliable change?

As a first step toward understanding which changes should be considered as meaningful, the authors assessed the reliability of quantitative functional tests on 5 consecutive days in 63 patients with MS, determining the range of measurement variability present when patients are clinically stable. Time to walk 25 feet (T25FW) and the 9-hole peg test (9HPT) varied by <20% of individual mean scores on repeated testing. Therefore, a 20% change on these tests can be considered to be the threshold that reliably indicates a true change in function for an individual.

The nature of the receptor site for the reversible K+ channel blocking by aminopyridines

This work presents a theoretical study aimed at the identification of the receptor site for the blocking of the voltage dependent K+ channels by protonated aminopyridines. Thus, the density functional theory (DFT) at the B3LYP/6-311 G (d,p) level is applied, both in vacuum and in solution, to a series of active (protonated) compounds: 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 3,4-diaminopyridine, and 4-aminoquinoleine. Analysis of the X-ray structure of the alpha-subunit of the channel shows that charged aminopyridines can interact electrostatically with a glutamic acid residue in the outside of the pore, or through a cation-pi interaction in the inside. To test both possibilities, model complexes are built using as nucleophiles a carboxylic group and an ethylene molecule, respectively. The three-dimensional electrostatic potential distribution of the protonated aminopyridines shows that an approaching nucleophile will be oriented toward the N-H (protonated) bond. Interaction with the carboxylic residue leads to a proton transfer, with the aminopyridine-carboxylic acid linked by a hydrogen bond. The observed breaking of the equivalence of the Laplacian of the charge density, the relative energy variation for the complexes, and the interaction with only one of the carboxylic residues in the fourfold alpha-subunit of the K+ channel are not compatible with the observed in vitro activity variation of aminopyridines. On the other hand, the study on the ethylene complexes shows, in vacuum and solution, a cation-pi interaction, clearly characterized by the atoms in molecules (AIM) theory. The variation of relative energy in solution is very small, but approaches the variation of in vitro activity. Our results, the pharmacophoric characteristics of aminopyridines, and the analysis of the three-dimensional internal structure of the K+ channel alpha-subunit suggest two putative receptor sites. One is formed by the four Thr-Thr-Val chains conforming the entrance to the narrow part of the inner K+ channel. The other is defined by four Thr residues within the pore.

Fatigue in progressive multiple sclerosis: results of a randomized, double-blind, placebo-controlled, crossover trial of oral 4-aminopyridine

Previous studies suggest that aminopyridine may play a role in the symptomatic treatment of fatigue in multiple sclerosis. Although the mechanism underlying the beneficial effect on fatigue remains unclear, it has been proposed that aminopyridines may help to improve conduction in demyelinated central pathways, implicating both axonal and synaptic mechanisms. The objective of the present study is to determine whether 4-AP decreases daily-living fatigue in progressive multiple sclerosis. The effect of 4-AP on other neurophysiological and neuropsychological parameters was also considered. A 'double-blind', randomized, 'placebo-controlled', crossover trial was conducted on 54 patients with progressive multiple sclerosis. All patients received treatment with placebo and 32 mg per day of 4-AP, each for 6 months. The main outcome measure was the Fatigue Severity Scale. Secondary measures were EDSS, cognitive functions and neurophysiological parameters. Forty-nine patients (91%) completed the study. Changes in fatigue scores, EDSS and cognitive functions were not significantly different between 4-AP and placebo. However, when patients treated with 4-AP were divided into two groups according to the serum level of 4-AP, a significant effect on fatigue compared with placebo was observed in the 'high level' (>30 ng/ml) group (P=0.05). Synchronization of motor evoked potentials improved during 4-AP with respect to placebo (P=0.019) and this correlated positively with fatigue reduction (P=0.010). No relevant side effects were observed.

Theoretical analysis of the molecular determinants responsible for the K(+) channel blocking by aminopyridines

This work presents a theoretical analysis of the molecular determinants responsible for the pharmacological activity (K(+) channel blocking) of aminopyridines. Thus, DFT theory at the B3LYP/cc-pVDZ level is applied to a series of active compounds: 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 3,4-diaminopyridine, and 4-aminoquinoleine. The two forms present in the biological environment, neutral and cationic (protonated), are considered in vacuum as well as in aqueous solution. The results show pyramidal and planar structures for the neutral and cationic forms, respectively. An analysis of the topology of the electron density show that an increase in conjugation between the pyridine ring and the amine group is responsible for the observed planarity of the protonated forms. By computing the Laplacian of the charge density we found the pyridine nitrogen to be the preferred protonation site, as a consequence of a much higher curvature of the charge density field. Also, from three-dimensional (3D) isoLaplacian diagrams a common reactivity pattern is only found in the charged forms. This reactivity pattern implies that interaction with the biological receptor site is mediated by electrostatic interactions and hydrogen bonding. Development of a physical-mathematical model allows identification of the specific relationship of the pharmacological activity index with the affinity for the receptor and the protonation ability.

Mobilization of calcium from intracellular stores, potentiation of neurotransmitter-induced calcium transients, and capacitative calcium entry by 4-aminopyridine

In this study we analyzed the effect of 4-aminopyridine (4-AP) on free cytosolic calcium concentration ([Ca(2+)](i)) in basal conditions, after stimulation with neurotransmitters, and during capacitative calcium entry. Using fura-2 ratiometric calcium imaging, we found that 4-AP increased [Ca(2+)](i) in type I astrocytes, neurons, and in skeletal muscle cells. The [Ca(2+)](i) elevation induced by 4-AP was concentration-dependent and consisted of two phases: the first was dependent on intracellular calcium mobilization, and the second was dependent on extracellular calcium influx. 4-AP also increased the second messenger inositol trisphosphate in both neurons and astrocytes. In astrocytes, 4-AP treatment potentiated the sustained phase of the [Ca(2+)](i) elevation induced by ATP and bradykinin. In addition, capacitative calcium entry was potentiated severalfold by 4-AP, in astrocytes and muscle cells but not in neurons. These effects of 4-AP were completely and promptly reversible. 4-AP blocked voltage-sensitive K(+) currents in astrocytes. However, voltage-sensitive K(+) channel blockers inhibiting these currents did not affect agonist-induced calcium transients or capacitative calcium entry, indicating that 4-AP effects on [Ca(2+)](i) were not caused by the blockade of voltage-gated K(+) channels. We conclude that 4-AP is able to affect calcium homeostasis at multiple levels, from increasing basal [Ca(2+)](i) to potentiating capacitative calcium entry. The potentiation of capacitative calcium entry in astrocytes or muscle cells may explain some of the therapeutic activities of 4-AP as a neurotransmission enhancer.

Aminopyridines for symptomatic treatment in multiple sclerosis

BACKGROUND

Because of their ability to increase nerve conduction in demyelinated nerve fibers, potassium channel blockers 4-aminopyridine (AP) and 3,4-diaminopyridine (DAP) have been proposed as a symptomatic therapy for people with multiple sclerosis (MS).

OBJECTIVES

To determine the efficacy and safety of aminopyridines in improving neurological deficits in people with MS.

SEARCH STRATEGY

Computerised general (MEDLINE, EMBASE) and specialised databases (Cochrane MS Group's trials register, CCTR). Hand search of bibliographic references from retrieved studies and recent MS symposia reports. Contact with principal investigators of known studies.

SELECTION CRITERIA

Trials were included if they fulfilled all following criteria: randomised controlled trials (RCTs); adults with MS, out of exacerbation; AP or DAP treatment versus placebo; clinical endpoints.

DATA COLLECTION AND ANALYSIS

We identified 26 potentially pertinent studies. Three reviewers independently extracted data and assessed trial quality from the 16 studies available as full papers.

MAIN RESULTS

Five studies (six publications) and 144 participants were considered in this review. Two more abstracts are awaiting assessment. All five studies were single-centre, double-blind, crossover trials. Four studies assessed the efficacy of AP versus placebo, one compared DAP with active placebo. The duration of treatment ranged from hours to three months. The median quality score of the studies was 3 (range 2-5). The heterogeneity of outcome assessment and the absence of information on individual study periods, allowed quantitative pooling of results for few categorical variables. Of the 144 treated patients, there were six major side effects: one acute encephalopathy, three episodes of confusion, and two seizures. Manual muscle testing was assessed in three studies (54 patients), with 29 patients (54%) improving in at least one muscular district during study treatment versus four patients (7%) during placebo (odds ratio [OR] 14.5, 95% confidence interval [CI] 4.7-43.7). Ambulation was assessed in three studies (54 patients): 9 patients (17%) improved during study treatment versus none during placebo (p<0.001). An improvement in EDSS score was found in 13 of the 144 participants during study treatment (9%) versus none during placebo (p<0.001). No improvement in neuropsychological tests was found in the two trials that evaluated cognitive function. Finally, 47 of 136 people with MS (35%) felt improved when receiving the study drug, against 7(5%) on placebo (OR 9.7, 95% CI 4.3-22.0).

REVIEWER'S CONCLUSIONS

Based on currently available information, no unbiased statement can be made about the safety or efficacy of aminopyridines for treating MS symptoms. Furthermore, we could not obtain any data on three unpublished RCTs involving more than 300 participants. We conclude that publication bias remains a pervasive problem in this area, and that until the results of these unpublished studies are available to the scientific community, no confident estimate of effectiveness of aminopyridines in the management of MS symptoms is possible.

Absorption characteristics of sustained-release 4-aminopyridine (fampridine SR) in patients with chronic spinal cord injury

Fampridine SR (4-aminopyridine) is a potassium channel-blocking drug currently being investigated for its therapeutic efficacy in ameliorating central conduction deficits due to demyelination in patients with spinal cord injury (SCI). The present open-label pharmacokinetic trial examined the absorption characteristics of a sustained-release form of the drug in 25 SCI subjects with chronic incomplete injuries. The overall group mean Cmax of 27.7 +/- 6.2 ng/mL occurred at a tmax of 3.4 +/- 1.4 hours. AUC0-12 was 210.5 +/- 49.5 ng/mL.h. For paraplegics, AUCtmax was 76.02 +/- 33.28 and for tetraplegics was significantly less at 51.25 +/- 20.36 (p = 0.037). A statistically significant difference in the initial rate and extent of absorption, but not in total 4-AP bioavailability over the 12-hour study period, was evident between tetraplegic patients, 0.60 +/- 0.23, and paraplegic patients, 0.39 +/- 0.14 (p = 0.02). There was a linear correlation (p < 0.05) between the neurological level of injury and Cmax/AUCtmax. These results confirm and extend previous observations of different rates of drug absorption among SCI patients with lesions above and below the sympathetic outflow (T6) and provide evidence of the absorption characteristics of this sustained-release form of 4-aminopyridine, which is helpful for optimal dosing.

The pathophysiology of multiple sclerosis: the mechanisms underlying the production of symptoms and the natural history of the disease

The pathophysiology of multiple sclerosis is reviewed, with emphasis on the axonal conduction properties underlying the production of symptoms, and the course of the disease. The major cause of the negative symptoms during relapses (e.g. paralysis, blindness and numbness) is conduction block, caused largely by demyelination and inflammation, and possibly by defects in synaptic transmission and putative circulating blocking factors. Recovery from symptoms during remissions is due mainly to the restoration of axonal function, either by remyelination, the resolution of inflammation, or the restoration of conduction to axons which persist in the demyelinated state. Conduction in the latter axons shows a number of deficits, particularly with regard to the conduction of trains of impulses and these contribute to weakness and sensory problems. The mechanisms underlying the sensitivity of symptoms to changes in body temperature (Uhthoff's phenomenon) are discussed. The origin of 'positive' symptoms, such as tingling sensations, are described, including the generation of ectopic trains and bursts of impulses, ephaptic interactions between axons and/or neurons, the triggering of additional, spurious impulses by the transmission of normal impulses, the mechanosensitivity of axons underlying movement-induced sensations (e.g. Lhermitte's phenomenon) and pain. The clinical course of the disease is discussed, together with its relationship to the evolution of lesions as revealed by magnetic resonance imaging and spectroscopy. The earliest detectable event in the development of most new lesions is a breakdown of the blood-brain barrier in association with inflammation. Inflammation resolves after approximately one month, at which time there is an improvement in the symptoms. Demyelination occurs during the inflammatory phase of the lesion. An important mechanism determining persistent neurological deficit is axonal degeneration, although persistent conduction block arising from the failure of repair mechanisms probably also contributes.

Human axons contain at least five types of voltage-dependent potassium channel

1. We investigated voltage-gated potassium channels in human peripheral myelinated axons; apart from the I, S and F channels already described in amphibian and rat axons, we identified at least two other channel types. 2. The I channel activated between -70 and -40 mV, and inactivated very slowly (time constant 13.1 s at -40 mV). It had two gating modes: the dominant ('noisy') mode had a conductance of 30 pS (inward current, symmetrical 155 mM K+) and a deactivation time constant (tau) of 25 ms (-80 mV); it accounted for most ( approximately 50-75 %) of the macroscopic K+ current in large patches. The secondary ('flickery') gating mode had a conductance of 22 pS, and showed bi-exponential deactivation (tau = 16 and 102 ms -80 11 mV); it contributed part of the slow macroscopic K+ current. 3. The I channel current was blocked by 1 microM alpha-dendrotoxin (DTX); we also observed two other DTX-sensitive K+ channel types (40 pS and 25 pS). The S and F channels were not blocked by 1 microM DTX. 4. The conductance of the S channel was 7-10 pS, and it activated at slightly more negative potentials than the I channel; its deactivation was slow (tau = 41.7 ms at -100 mV). It contributed a second component of the slow macroscopic K+ current. 5. The F channel had a conductance of 50 pS; it activated at potentials between -40 and +40 V, deactivated very rapidly (tau = 1.4 ms at -100 mV), and inactivated rapidly (tau = 62 ms at +80 mV). It accounted for the fast-deactivating macroscopic K+ current and partly for fast K+ current inactivation. 6. We conclude that human and rat axonal K+ channels are closely similar, but that the correspondence between K+ channel types and the macroscopic currents usually attributed to them is only partial. At least five channel types exist, and their characteristics overlap to a considerable extent.

Safety and efficacy of 4-aminopyridine in humans with spinal cord injury: a long-term, controlled trial

STUDY OBJECTIVE

To determine the effects of the long-term administration of 4-aminopyridine (4-AP) on sensorimotor function in humans with long-standing spinal cord injury (SCI).

DESIGN

Randomized, open-label, active-treatment control, dosage-blinded study.

SETTING

University-affiliated, tertiary-level care, Department of Veterans Affairs Medical Center.

PATIENTS

Twenty-one healthy men and women outpatients suffering from traumatic SCI (14 tetraplegic, 7 paraplegic) for 2 years or more.

INTERVENTIONS

Dosages of an immediate-release formulation of 4-AP were titrated. At 3 months, 16 subjects were receiving 4-AP 30 mg/day (high dose); 5 subjects were receiving 4-AP 6 mg/day (low dose) and served as an active-treatment control group.

MEASUREMENTS AND MAIN RESULTS

Composite motor and sensory scores had statistically significant increases at 3 months. Maximal expiratory pressure, maximal inspiratory pressure, forced vital capacity, and forced expiratory volume in 1 second showed clinically meaningful and/or statistically significant increases among patients receiving 4-AP 30 mg/day. These subjects also had significant decreases in spasticity (modified Ashworth Scale). Serial biochemical profiles and electroencephalographs were unchanged from baseline, and no clinically significant drug toxicity was encountered.

CONCLUSIONS

Long-term oral administration of immediate-release 4-AP was associated with improvement in and recovery of sensory and motor function, enhanced pulmonary function, and diminished spasticity in patients with long-standing SCI. 4-Aminopyridine appears to be safe and relatively free from toxicity when administered orally over 3 months. Each patient who received immediate-release 4-AP 30 mg/day showed a response in one or more of the outcome measures.

Treatment of multiple sclerosis: recent trials and future perspectives

In the past year, further evidence establishing the usefulness of beta interferons and glatiramer in the treatment of relapsing-remitting multiple sclerosis has been advanced. Interferon-beta-1b was also shown to be efficacious in secondary progressive multiple sclerosis. This and other trials of symptomatic treatments are reviewed. Based on an appraisal of recent experimental studies, future promising approaches to intervene in the chain of immunopathogenetic events are discussed.

Recent developments in drug therapy for multiple sclerosis

Symptomatic treatment of multiple sclerosis (MS) includes a diverse range of drugs intended to relieve the specific symptoms with which a patient may present at a particular point in the progression of the disease. These drugs, not specifically designed for the treatment of MS, may include antispastic agents (e.g. baclofen), drugs to reduce tremor (e.g. clonazepam), anticholinergics (e.g. oxybutynin) which relieve urinary symptoms, anti-epileptics (e.g. carbamazepine) to control neuralgia, stimulants to reduce fatigue (e.g. amantadine), and antidepressants (e.g. fluoxetine) to treat depression. The treatment of acute relapses or exacerbations is dominated by corticosteroids such as methylprednisolone. The most active area of current investigation is the development of drugs which will inhibit the progression of the disease process itself, and in this category the beta- and alpha-interferons are the most effective drugs currently available, although many new treatments are currently in trials, including immunoglobulin, copolymer-1. bovine myelin, T-cell receptor (TCR) peptide vaccines, platelet activating factor (PAF) antagonists, matrix metallo-proteinase inhibitors, campath-1, and insulin-like growth factor (IGF).

Dynamic potassium channel distributions during axonal development prevent aberrant firing patterns

The distribution and function of Shaker-related K+ channels were studied with immunofluorescence and electrophysiology in sciatic nerves of developing rats. At nodes of Ranvier, Na+ channel clustering occurred very early (postnatal days 1-3). Although K+ channels were not yet segregated at most of these sites, they were directly involved in action potential generation, reducing duration, and the refractory period. At approximately 1 week, K+ channel clusters were first seen but were within the nodal gap and in paranodes, and only later (weeks 2-4) were they shifted to juxtaparanodal regions. K+ channel function was most dramatic during this transition period, with block producing repetitive firing in response to single stimuli. As K+ channels were increasingly sequestered in juxtaparanodes, conduction became progressively insensitive to K+ channel block. Over the first 3 weeks, K+ channel clustering was often asymmetric, with channels exclusively in the distal paranode in approximately 40% of cases. A computational model suggested a mechanism for the firing patterns observed, and the results provide a role for K+ channels in the prevention of aberrant excitation as myelination proceeds during development.

Alkoxypsoralens, novel nonpeptide blockers of Shaker-type K+ channels: synthesis and photoreactivity

A series of psoralens and structurally related 5,7-disubstituted coumarins was synthesized and investigated for their K+ channel blocking activity as well as for their phototoxicity to Artemia salina and their ability to generate singlet oxygen and to photomodify DNA. After screening the compounds on Ranvier nodes of the toad Xenopus laevis, the affinities of the most promising compounds, which proved to be psoralens bearing alkoxy substituents in the 5-position or alkoxymethyl substituents in the neighboring 4- or 4'-position, to a number of homomeric K+ channels were characterized. All compounds exhibited the highest affinity to Kv1.2. 5,8-Diethoxypsoralen (10d) was found to be an equally potent inhibitor of Kv1.2 and Kv1.3, while lacking the phototoxicity normally inherent in psoralens. The reported compounds represent a novel series of nonpeptide blockers of Shaker-type K+ channels that could be further developed into selective inhibitors of Kv1.2 or Kv1. 3.

Correlation between symptom fatigue and muscular fatigue in multiple sclerosis

The symptom of fatigue is a frequent complaint in multiple sclerosis (MS) patients. Signs of fatigability have been documented in these patients as well. However, correlation with signs of objective fatigue had not been clarified in MS. The aim of this study was to ascertain the existence of muscular fatigue in multiple sclerosis patients, and to find out if there is a correlation between the subjective symptom of fatigue and muscular fatigue. Fifty MS patients and 50 age and sex matched volunteers were studied using isometric and isotonic tests using the dominant hand. Strength was studied in the baseline condition and also after recovery of either an isotonic (experiment A) or isometric effort (experiment B). Maximum strength, strength in relationship to weight, slope of fatigability in 11 consecutive contractions, and strength and duration of a maximum effort were calculated. Fatigue as a symptom was measured using the Fatigue Severity Scale (FSS) and the Fatigue Descriptive Scale (FDS). Non-parametric techniques were used for the statistical analysis. Patients with MS had less isometric and isotonic strength, but the recovery was the same as recovery in the control group. There was a negative linear correlation between the symptom of fatigue and the baseline strength. In conclusion, this study supports the existence of signs of muscular fatigue in MS patients. However, the recovery after exercise is normal. The correlation between the baseline scores in strength and the symptom of fatigue suggest that the same cause (probably pyramidal deficits) may be involved in both of them. Copyright 1998 Lippincott Williams & Wilkins

Randomized double-blind crossover trial of fampridine-SR (sustained release 4-aminopyridine) in patients with incomplete spinal cord injury

A randomized double-blind dose-titration crossover trial of the safety and efficacy of oral fampridine-SR (sustained release 4-aminopyridine) was conducted on spinal cord injured (SCI) patients at two centers. Twenty-six patients (n = 26) with incomplete lesions completed the trial. These patients all had chronic (>2 years) and stable neurological deficits. They received fampridine-SR 12.5 and 17.5 mg b.i.d. over a 2-week treatment period, followed by a 1-week washout and 2 weeks of placebo, or vice versa. Patients reported significant benefit of fampridine-SR over placebo on patient satisfaction (McNemar's test, p2 < 0.05) and quality of life scores (p2 < 0.01). Sensory scores (p1 < 0.01), including both pin prick (p1 = 0.059) and light touch (p1 = 0.058), and motor scores (adjusted to reflect only paretic segments) (p1 < 0.01) all yielded evidence of benefit of fampridine-SR over placebo. The Ashworth scale of spasticity was significantly (p2 < 0.05) reduced when patients received fampridine-SR. There were no statistically significant benefits of the drug on measures of pain or bowel, bladder and sexual function, or functional independence. Side effects of lightheadedness and nausea were transient and trivial relative to efficacy, and approximately 30% of patients reported a wish to continue to use fampridine-SR. The clinical benefits most likely derive from the K+ channel blocking action of the drug. Potassium channel blockade enhances axonal conduction across demyelinated internodes and enhances neuroneuronal and neuromuscular transmission in preserved axons. These results provide the first evidence of therapeutic benefit of fampridine-SR in SCI patients.