The importance of voltage-dependent sodium channels in cerebral ischaemia

Therapeutic Administration of Oxcarbazepine Saves Cerebellar Purkinje Cells from Ischemia and Reperfusion Injury Induced by Cardiac Arrest through Attenuation of Oxidative Stress

Research reports using animal models of ischemic insults have demonstrated that oxcarbazepine (a carbamazepine analog: one of the anticonvulsant compounds) extends neuroprotective effects against cerebral or forebrain injury induced by ischemia and reperfusion. However, research on protective effects against ischemia and reperfusion cerebellar injury induced by cardiac arrest (CA) and the return of spontaneous circulation has been poor. Rats were assigned to four groups as follows: (Groups 1 and 2) sham asphyxial CA and vehicle- or oxcarbazepine-treated, and (Groups 3 and 4) CA and vehicle- or oxcarbazepine-treated. Vehicle (0.3% dimethyl sulfoxide/saline) or oxcarbazepine (200 mg/kg) was administered intravenously ten minutes after the return of spontaneous circulation. In this study, CA was induced by asphyxia using vecuronium bromide (2 mg/kg). We conducted immunohistochemistry for calbindin D-28kDa and Fluoro-Jade B histofluorescence to examine Purkinje cell death induced by CA. In addition, immunohistochemistry for 4-hydroxy-2-nonenal (4HNE) was carried out to investigate CA-induced oxidative stress, and immunohistochemistry for Cu, Zn-superoxide dismutase (SOD1) and Mn-superoxide dismutase (SOD2) was performed to examine changes in endogenous antioxidant enzymes. Oxcarbazepine treatment after CA significantly increased the survival rate and improved neurological deficit when compared with vehicle-treated rats with CA (survival rates ≥ 63.6 versus 6.5%), showing that oxcarbazepine treatment dramatically protected cerebellar Purkinje cells from ischemia and reperfusion injury induced by CA. The salvation of the Purkinje cells from ischemic injury by oxcarbazepine treatment paralleled a dramatic reduction in 4HNE (an end-product of lipid peroxidation) and increased or maintained the endogenous antioxidant enzymes (SOD1 and SOD2). In brief, this study shows that therapeutic treatment with oxcarbazepine after CA apparently saved cerebellar neurons (Purkinje cells) from CA-induced neuronal death by attenuating oxidative stress and suggests that oxcarbazepine can be utilized as a therapeutic medicine for ischemia and reperfusion brain (cerebellar) injury induced by CA.

Swelling and membrane potential dynamics of glial Müller cells

Presently a detailed biophysical model describing reversible and irreversible swelling dynamics of Müller cells (MC) is reported. The model includes a biophysical block of ionic and neutral species transport via MC membrane, water transport induced by osmotic pressure and pressure generated by membrane deformations, MC membrane potential and membrane mechanical properties. The model describes reversible and irreversible MC swelling (MCS) using the same set of parameters. The model was used in fitting available experimental data, and produced numerical values of previously unknown model parameters, including those describing mechanical properties of Müller cell membrane (MCM) with respect to bending and stretching. Numerical experiments simulating MC swelling showed complex oscillation dynamics of the relevant parameters in physiological initial conditions. In particular, MC membrane potential (ΔΨ_MC) demonstrated complex oscillation dynamics, which may be described by a superposition of several oscillations with their periods in the milliseconds, 100-ms and seconds time ranges. Dynamics of reversible and irreversible MCS, and the transition criteria from reversible to irreversible MCS modes were determined in model simulations.

Pan-cerebral sodium elevations in vascular dementia: Evidence for disturbed brain-sodium homeostasis

Vascular dementia (VaD) is the second most common cause of cognitive impairment amongst the elderly. However, there are no known disease-modifying therapies for VaD, probably due to incomplete understanding of the molecular basis of the disease. Despite the complex etiology of neurodegenerative conditions, a growing body of research now suggests the potential involvement of metal dyshomeostasis in the pathogenesis of several of the age-related dementias. However, by comparison, there remains little research investigating brain metal levels in VaD. In order to shed light on the possible involvement of metal dyshomeostasis in VaD, we employed inductively coupled plasma-mass spectrometry to quantify the levels of essential metals in post-mortem VaD brain tissue (n = 10) and age-/sex-matched controls (n = 10) from seven brain regions. We found novel evidence for elevated wet-weight cerebral sodium levels in VaD brain tissue in six out of the seven regions analyzed. Decreased cerebral-potassium levels as well as increased Na/K ratios (consistent with high tissue sodium and low potassium levels) were also observed in several brain regions. These data suggest that reduced Na⁺/K⁺-exchanging ATPase (EC 7.2.2.13) activity could contribute to the contrasting changes in sodium and potassium measured here.

Pathophysiology and Treatment of Stroke: Present Status and Future Perspectives

Stroke is the second leading cause of death and a major contributor to disability worldwide. The prevalence of stroke is highest in developing countries, with ischemic stroke being the most common type. Considerable progress has been made in our understanding of the pathophysiology of stroke and the underlying mechanisms leading to ischemic insult. Stroke therapy primarily focuses on restoring blood flow to the brain and treating stroke-induced neurological damage. Lack of success in recent clinical trials has led to significant refinement of animal models, focus-driven study design and use of new technologies in stroke research. Simultaneously, despite progress in stroke management, post-stroke care exerts a substantial impact on families, the healthcare system and the economy. Improvements in pre-clinical and clinical care are likely to underpin successful stroke treatment, recovery, rehabilitation and prevention. In this review, we focus on the pathophysiology of stroke, major advances in the identification of therapeutic targets and recent trends in stroke research.

Post-treatment with oxcarbazepine confers potent neuroprotection against transient global cerebral ischemic injury by activating Nrf2 defense pathway

Oxcarbazepine (OXC), a voltage-gated sodium channel blocker, is an antiepileptic medication and used for the bipolar disorders treatment. Some voltage-gated sodium channel blockers have been demonstrated to display strong neuroprotective properties in models of cerebral ischemia. However, neuroprotective effects and mechanisms of OXC have not yet been reported. Here, we investigated the protective effect of OXC and its mechanisms in the cornu ammonis 1 subfield (CA1) of gerbils subjected to 5 min of transient global cerebral ischemia (tGCI). tGCI led to death of most pyramidal neurons in CA1 at 5 days after ischemia. OXC (100 and 200 mg/kg) was intraperitoneally administered once at 30 min after tGCI. Treatment with 200 mg/kg, not 100 mg/kg OXC, significantly protected CA1 pyramidal neurons from tGCI-induced injury. OXC treatment significantly decreased superoxide anion production, 4-hydroxy-2-nonenal and 8-hydroxyguanine levels in ischemic CA1 pyramidal neurons. In addition, the treatment restored levels of superoxide dismutases, catalase, and glutathione peroxidase. Furthermore, the treatment distinctly inhibited tGCI-induced microglia activation and significantly reduced levels of pro-inflammatory cytokines (interleukin-1β and tumor necrosis factor-α). In particular, OXC treatment significantly enhanced expressions of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream protein heme oxygenase-1 in ischemic CA1. The neuroprotective effects of OXC were abolished by brusatol (an inhibitor of Nrf2). Taken together, these results indicate that post-treatment of OXC can display neuroprotection against brain injuries following ischemic insults. This neuroprotection may be displayed by attenuation of oxidative stress and neuroinflammation, which can be mediated by activation of Nrf2 pathway.

A Biophysical Model for Cytotoxic Cell Swelling

We present a dynamic biophysical model to explain neuronal swelling underlying cytotoxic edema in conditions of low energy supply, as observed in cerebral ischemia. Our model contains Hodgkin-Huxley-type ion currents, a recently discovered voltage-gated chloride flux through the ion exchanger SLC26A11, active KCC2-mediated chloride extrusion, and ATP-dependent pumps. The model predicts changes in ion gradients and cell swelling during ischemia of various severity or channel blockage with realistic timescales. We theoretically substantiate experimental observations of chloride influx generating cytotoxic edema, while sodium entry alone does not. We show a tipping point of Na⁺/K⁺-ATPase functioning, where below cell volume rapidly increases as a function of the remaining pump activity, and a Gibbs-Donnan-like equilibrium state is reached. This precludes a return to physiological conditions even when pump strength returns to baseline. However, when voltage-gated sodium channels are temporarily blocked, cell volume and membrane potential normalize, yielding a potential therapeutic strategy.

SIGNIFICANCE STATEMENT

Cytotoxic edema most commonly results from energy shortage, such as in cerebral ischemia, and refers to the swelling of brain cells due to the entry of water from the extracellular space. We show that the principle of electroneutrality explains why chloride influx is essential for the development of cytotoxic edema. With the help of a biophysical model of a single neuron, we show that a tipping point of the energy supply exists, below which the cell volume rapidly increases. We simulate realistic time courses to and reveal critical components of neuronal swelling in conditions of low energy supply. Furthermore, we show that, after transient blockade of the energy supply, cytotoxic edema may be reversed by temporary blockade of Na⁺ channels.

Bioactive marine drugs and marine biomaterials for brain diseases

Marine invertebrates produce a plethora of bioactive compounds, which serve as inspiration for marine biotechnology, particularly in drug discovery programs and biomaterials development. This review aims to summarize the potential of drugs derived from marine invertebrates in the field of neuroscience. Therefore, some examples of neuroprotective drugs and neurotoxins will be discussed. Their role in neuroscience research and development of new therapies targeting the central nervous system will be addressed, with particular focus on neuroinflammation and neurodegeneration. In addition, the neuronal growth promoted by marine drugs, as well as the recent advances in neural tissue engineering, will be highlighted.

Neurological perspectives on voltage-gated sodium channels

The activity of voltage-gated sodium channels has long been linked to disorders of neuronal excitability such as epilepsy and chronic pain. Recent genetic studies have now expanded the role of sodium channels in health and disease, to include autism, migraine, multiple sclerosis, cancer as well as muscle and immune system disorders. Transgenic mouse models have proved useful in understanding the physiological role of individual sodium channels, and there has been significant progress in the development of subtype selective inhibitors of sodium channels. This review will outline the functions and roles of specific sodium channels in electrical signalling and disease, focusing on neurological aspects. We also discuss recent advances in the development of selective sodium channel inhibitors.

Anoxic depolarization of hippocampal astrocytes: possible modulation by P2X7 receptors

Current responses from CA1 neurons and stratum oriens astrocytes were recorded from hippocampal brain slices by means of the whole-cell patch-clamp technique. Anoxic depolarization (AD) was induced by an oxygen/glucose-deprived (OGD) medium also containing sodium iodoacetate and antimycin, in order to block glycolysis and oxidative phosphorylation, respectively. Anoxic depolarization has been reported to be due to the sudden increase of the extracellular K(+) concentration and the accompanying explosive rise in glutamate concentration. We asked ourselves whether the release of ATP activating P2X7 receptors is also involved in the AD. Although, the AD was evoked in absolute synchrony in neurons and astrocytes, and the NMDA receptor antagonistic AP-5 depressed these responses, neither the non-selective P2 receptor antagonist PPADS, nor the highly selective P2X7 receptor antagonist A438079 interfered with the AD or its delay time in neurons/astrocytes after inducing chemical hypoxia. However, A438079, but not PPADS increased in astrocytes the slow inward current observed in a hypoxic medium. It is concluded that ATP co-released with glutamate by hypoxic stimulation has only a minor function in the present brain slice system.

Pharmacology of dimethyl sulfoxide in cardiac and CNS damage

The pharmacological effects of dimethyl sulfoxide (DMSO) administration include some desirable properties that may be useful in the treatment of medical disorders resulting in tissue injury and compromised organ systems. These properties include the reported effects of DMSO on impaired blood flow, suppression of cytotoxicity from excess glutamate release that may result in lethal NMDA-AMPA activation, restriction of cytotoxic Na(+) and Ca(2+) entry into damaged cells, blocking tissue factor (TF) from contributing to thrombosis, reduction of intracranial pressure, tissue edema, and inflammatory reactions, and inhibition of vascular smooth muscle cell migration and proliferation that can lead to atherosclerosis of the coronary, peripheral, and cerebral circulation. A review of the basic and clinical literature on the biological actions of DMSO in cardiac and central nervous system (CNS) damage or dysfunction indicates that this agent, alone or in combination with other synergistic molecules, has been reported to neutralize or attenuate pathological complications that harmed or can further harm these two organ systems. The effects of DMSO make it potentially useful in the treatment of medical disorders involving head and spinal cord injury, stroke, memory dysfunction, and ischemic heart disease.

Potential Roles of Electrogenic Ion Transport and Plasma Membrane Depolarization in Apoptosis

Apoptosis is characterized by the programmed activation of specific biochemical pathways leading to the organized demise of cells. To date, aspects of the intracellular signaling machinery involved in this phenomenon have been extensively dissected and characterized. However, recent studies have elucidated a novel role for changes in the intracellular milieu of the cells as important modulators of the cell death program. Specially, intracellular ionic homeostasis has been reported to be a determinant in both the activation and progression of the apoptotic cascade. Several apoptotic insults trigger specific changes in ionic gradients across the plasma membrane leading to depolarization of the plasma membrane potential (PMP). These changes lead to ionic imbalance early during apoptosis. Several studies have also suggested the activation and/or modulation of specific ionic transport mechanisms including ion channels, transporters and ATPases, as mediators of altered intracellular ionic homeostasis leading to PMP depolarization during apoptosis. However, the role of PMP depolarization and of the changes in ionic homeostasis during the progression of apoptosis are still unclear. This review summarizes the current knowledge regarding the causes and consequences of PMP depolarization during apoptosis. We also review the potential electrogenic ion transport mechanisms associated with this event, including the net influx/efflux of cations and anions. An understanding of these mechamisms could lead to the generation of new therapeutic approaches for a variety of diseases involving apoptosis.

Sodium channel blocking activity of AM-36 and sipatrigine (BW619C89): in vitro and in vivo evidence

Sodium channel blockers are neuroprotective against cerebral ischemia in animal models. A novel neuroprotective compound AM-36, when screened for activity at the most common receptor and ion channel binding sites, revealed activity at site 2 Na+ channels. Studies then investigated this Na+ channel blocking activity in vitro and in vivo relative to other Na+ channel blockers, including the neuroprotective agent sipatrigine (BW619C89). AM-36 inhibited batrachotoxinin (BTX)-sensitive Na+ channel binding in rat brain homogenates with an IC50 of 0.28 microM. Veratridine (100 microM)-induced neurotoxicity in murine cerebellar granule cells was completely inhibited by AM-36 (1.7 microM) compared to only partial inhibition by sipatrigine (26 microM). Veratridine-stimulated glutamate release, as measured through a microdialysis probe in the cortex of anesthetised rats, was inhibited by 90% by superfusion of AM-36 (1000 microM). In the endothelin-1 (ET-1) model of middle cerebral artery occlusion (MCAo) in conscious rats, both AM-36 (6 mg/kg i.p.) and sipatrigine (10 mg/kg i.p.) 30 min post-MCAo significantly reduced cortical, but not striatal infarct volume. As the refractiveness of the striatum is likely to be dependent on the route and time of drug administration, AM-36 (1 mg/kg i.v.) was administered 3 or 5 h after MCAo and significantly reduced both cortical and striatal infarct volumes. The present studies demonstrate Na+ channel blocking activity of AM-36 both in vitro and in vivo, together with significant neuroprotection when administration is delayed up to 5 h following experimental stroke.

Structures of μO-conotoxins from Conus marmoreus

The microO-conotoxins are an intriguing class of conotoxins targeting various voltage-dependent sodium channels and molluscan calcium channels. In the current study, we have shown MrVIA and MrVIB to be the first known peptidic inhibitors of the transient tetrodotoxin-resistant (TTX-R) Na(+) current in rat dorsal root ganglion neurons, in addition to inhibiting tetrodotoxin-sensitive Na(+) currents. Human TTX-R sodium channels are a therapeutic target for indications such as pain, highlighting the importance of the microO-conotoxins as potential leads for drug development. Furthermore, we have used NMR spectroscopy to provide the first structural information on this class of conotoxins. MrVIA and MrVIB are hydrophobic peptides that aggregate in aqueous solution but were solubilized in 50% acetonitrile/water. The three-dimensional structure of MrVIB consists of a small beta-sheet and a cystine knot arrangement of the three-disulfide bonds. It contains four backbone "loops" between successive cysteine residues that are exposed to the solvent to varying degrees. The largest of these, loop 2, is the most disordered part of the molecule, most likely due to flexibility in solution. This disorder is the most striking difference between the structures of MrVIB and the known delta- and omega-conotoxins, which along with the microO-conotoxins are members of the O superfamily. Loop 2 of omega-conotoxins has previously been shown to contain residues critical for binding to voltage-gated calcium channels, and it is interesting to speculate that the flexibility observed in MrVIB may accommodate binding to both sodium and molluscan calcium channels.

The sodium channel blocker RS100642 reverses down-regulation of the sodium channel alpha-subunit Na(v) 1.1 expression caused by transient ischemic brain injury in rats

In this study we evaluated the expression of five sodium channel (NaCh) Alpha-subunit genes after transient middle cerebral artery occlusion (MCAo) in the rat and the effects of treatment with the NaCh blocker and experimental neuroprotective agent RS100642 as compared to the prototype NaCh blocker mexiletine. The expression of Na(v) 1.1, Na(v) 1.2, Na(v) 1.3, Na(v) 1.7, Na(v) 1.8 and the housekeeping gene beta-actin were studied in vehicle or drug-treated rats at 6, 24 and 48 h post-MCAo using real-time quantitative RT-PCR. RS100642 (1 mg/kg), mexiletine (10 mg/kg), or vehicle (1 ml/kg) was injected (i.v.) at 30 min, 2, 4, and 6 h post-injury. Following MCAo only the Na(v) 1.1 and Na(v) 1.2 genes were significantly down-regulated in the ipsilateral hemisphere of the injured brains. RS100642 treatment significantly reversed the down-regulation of Na(v) 1.1 (but not Na(v) 1.2) at 24-48 h post-injury. Mexiletine treatment, on the other hand, had no significant effect on the down-regulation of either gene. These findings demonstrate that treatment with a neuroprotective dose of RS100642 significantly reverses the down-regulation of Na(v) 1.1 caused by ischemic brain injury and suggests that RS100642 selectively targets the Na(v) 1.1 Alpha-subunit of the NaCh. Furthermore, our findings strengthen the hypothesis that ischemic injury may produce selective depletion of voltage-gated NaChs, and suggest that the Na(v) 1.1 NaCh Alpha-subunit may play a key role in the neuronal injury/recovery process.

Solution structure of mu-conotoxin PIIIA, a preferential inhibitor of persistent tetrodotoxin-sensitive sodium channels

Mu-conotoxins are peptide inhibitors of voltage-sensitive sodium channels (VSSCs). Synthetic forms of mu-conotoxins PIIIA and PIIIA-(2-22) were found to inhibit tetrodotoxin (TTX)-sensitive VSSC current but had little effect on TTX-resistant VSSC current in sensory ganglion neurons. In rat brain neurons, these peptides preferentially inhibited the persistent over the transient VSSC current. Radioligand binding assays revealed that PIIIA, PIIIA-(2-22), and mu-conotoxins GIIIB discriminated among TTX-sensitive VSSCs in rat brain, that these and GIIIC discriminated among the corresponding VSSCs in human brain, and GIIIA had low affinity for neuronal VSSCs. (1)H NMR studies found that PIIIA adopts two conformations in solution due to cis/trans isomerization at hydroxyproline 8. The major trans conformation results in a three-dimensional structure that is significantly different from the previously identified conformation of mu-conotoxins GIIIA and GIIIB that selectively target TTX-sensitive muscle VSSCs. Comparison of the structures and activity of PIIIA to muscle-selective mu-conotoxins provides an insight into the structural requirements for inhibition of different TTX-sensitive sodium channels by mu-conotoxins.

Neuroprotective effects of the sodium channel blocker RS100642 and attenuation of ischemia-induced brain seizures in the rat

Seizurogenic activity develops in many patients following brain injury and may be involved in the pathophysiological effects of brain trauma and stroke. We have evaluated the effects of the use-dependent sodium channel blocker RS100642, an analog of mexiletine, as a neuroprotectant and anti-seizure agent in a rat model of transient middle cerebral artery occlusion (MCAo). Post-injury treatment with RS100642 (0.01-5.0 mg/kg) dose-dependently reduced brain infarction, improved functional recovery of electroencephalographic (EEG) power, and improved neurological outcome following 2 h of MCAo and 24 h recovery. This effect was more potent and offered a larger reduction of brain infarct volume than a maximal neuroprotective dose of mexiletine (10.0 mg/kg). Furthermore, brain seizure activity recorded following 1 h MCAo and 72 h of recovery in injured rats was either completely blocked (30 min pre-MCAo treatment) or significantly reduced (30 min post-MCAo treatment) with RS100642 (1.0 mg/kg) treatment resulting in greater than 60% reduction of core brain infarct. These results indicate that brain seizure activity during MCAo likely contributes to the pathophysiology of brain injury and that RS100642 may be an effective neuroprotective treatment not only to decrease brain injury but also to reduce the pathological EEG associated with focal ischemia.

Differential pattern of expression of voltage-gated sodium channel genes following ischemic brain injury in rats

This study investigated the effects of brain ischemia on sodium channel gene (NaCh) expression in rats. Using quantitative RT-PCR, our findings demonstrated the expression ratio of NaCh genes in normal rat brain to be Na(v)1.1 > Na(v)1.8 > Na(v)1.3 > Na(v)1.7 (rBI > PN3 > rBIII > PN1). In contrast, brain injury caused by middle cerebral artery occlusion (MCAo) for 2 h followed by reperfusion significantly down-regulated Na(v)1.3 and Na(v)1.7 genes in both injured and contralateral hemispheres; whereas the Na(v)1.8 gene was down regulated in only the injured hemisphere (though only acutely at 2 or 2-6 h post-MCAo). However, the time-course of NaCh gene expression revealed a significant down-regulation of Na(v)1.1 only in the ischemic hemisphere beginning 6 h post-MCAo and measured out to 48 h post-MCAo. In a separate preliminary study Na(v)1.2 (rBII) gene was found to be expressed at levels greater than that of Na(v)1.1 in normal rats and was significantly down regulated at 24 h post-MCAo). Our findings document, for the first time, quantitative and relative changes in the expression of various NaCh genes following ischemic brain injury and suggest that the Na(v)1.1 sodium channel gene may play a key role in ischemic injury/recovery.

A novel voltage-sensitive Na(+) and Ca(2+) channel blocker, NS-7, prevents suppression of cyclic AMP-dependent protein kinase and reduces infarct area in the acute phase of cerebral ischemia in rat

Binding of cyclic AMP to the regulatory subunit of cyclic AMP-dependent protein kinase (PKA) is an essential step in cyclic AMP-mediated intracellular signal transduction. This binding is, however, rapidly inhibited in the acute phase of cerebral ischemia, indicating that the signal transduction via PKA is very vulnerable to ischemia, although this signal pathway is very important for neuronal survival in the brain. Several lines of evidence suggest that the activation of voltage-sensitive Na+ and Ca(2+) channels is an important mediator of acute ischemic brain damage. In the present study, therefore, we examined the effect of a novel Na+ and Ca(2+) channel blocker, NS-7 (4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride), on changes in the binding activity of PKA to cyclic AMP in permanent focal cerebral ischemia, which was induced by occlusion of the middle cerebral artery by the intraluminal suture method for 5 h in the rat. NS-7 (1 mg/kg) or saline was intravenously infused 5 min after occlusion. The binding activity of PKA to cyclic AMP and local cerebral blood flow were assessed by the in vitro [(3)H]cyclic AMP binding and the [(14)C]iodoantipyrine methods, respectively. NS-7 significantly suppressed inhibition of the binding activity of PKA to cyclic AMP in the ischemic regions such as the frontal and parietal cortices and the medial region of the caudate-putamen without affecting cerebral blood flow or arterial blood pressure. Infarct area measured in the brain slices stained with cresyl violet was significantly smaller in animals treated with NS-7 than in those treated with saline. Blockade of voltage-sensitive Na+ and Ca(2+) channels by NS-7 was expected to reduce ischemia-induced depolarization and thus prevent a massive formation of free radicals, which is known to inhibit the binding activity of PKA to cyclic AMP. These data clearly indicate that NS-7 provides very efficient neuroprotection in the acute phase of cerebral ischemia, and sustains the normal function of PKA.

Ischemic stroke in elderly patients treated with a free radical scavenger-glycolytic intermediate solution: a preliminary pilot trial

The safety and tolerability of a free radical scavenger with Na+ channel blocking activity (dimethyl sulfoxide (DMSO)) combined with a glycolytic intermediate and high energy substrate (fructose 1,6-disphosphate (FDP)) were assessed in a mostly elderly patient group presenting with acute and subacute ischemic stroke. Eleven patients (average age 65) were given i.v. infusions of DMSO-FDP twice daily for an average of 12 days, while five control patients (average age 63) were given standard therapy. Safety and tolerability were evaluated by clinical adverse effects to drug therapy. Efficacy of DMSO-FDP was assessed by MRI lesion size, by magnetic resonance angiography of ischemic territory, and by a 5-point neurologic recovery scale that rated sensory-motor function and level of consciousness. Results suggest that DMSO-FDP administration is safe, well-tolerated and may be of benefit when given within 12 h after the onset of stroke symptoms. No significant changes in blood pressure, EKG, heart rate or hematology and chemistry profiles, were recorded in any patient receiving DMSO-FDP. Neurologic evaluation at 1, 3 and 6 months after treatments revealed that 7 of 11 (63%) patients given DMSO-FDP achieved 'improved' or 'markedly improved' status while 1 of 5 (20%) standard treated patients showed 'improved' status and only at the 3-month follow-up. This preliminary trial indicates that DMSO-FDP is well tolerated by this group of elderly patients and could be of benefit in reducing neurologic disability after stroke.

Incorporation of sodium channel blocking and free radical scavenging activities into a single drug, AM-36, results in profound inhibition of neuronal apoptosis

AM-36 is a novel neuroprotective agent incorporating both antioxidant and Na(+) channel blocking actions. In cerebral ischaemia, loss of cellular ion homeostasis due to Na(+) channel activation, together with increased reactive oxygen species (ROS) production, are thought to contribute to neuronal death. Since neuronal death in the penumbra of the ischaemic lesion is suggested to occur by apoptosis, we investigated the ability of AM-36, antioxidants and Na(+) channel antagonists to inhibit toxicity induced by the neurotoxin, veratridine in cultured cerebellar granule cells (CGC's). Veratridine (10 - 300 microM) concentration-dependently reduced cell viability of cultured CGC's. Under the experimental conditions employed, cell death induced by veratridine (100 microM) possessed the characteristics of apoptosis as assessed by morphology, TUNEL staining and DNA laddering on agarose gels. Neurotoxicity and apoptosis induced by veratridine (100 microM) were inhibited to a maximum of 50% by the antioxidants, U74500A (0.1 - 10 microM) and U83836E (0.03 - 10 microM), and to a maximum of 30% by the Na(+) channel blocker, dibucaine (0.1 - 100 microM). In contrast, AM-36 (0.01 - 10 microM) completely inhibited veratridine-induced toxicity ( IC(50) 1.7 (1.5 - 1.9) microM, 95% confidence intervals (CI) in parentheses) and concentration-dependently inhibited apoptosis. These findings suggest veratridine-induced toxicity and apoptosis are partially mediated by generation of ROS. AM-36, which combines both Na(+) channel blocking and antioxidant activity, provided superior neuroprotection compared with agents possessing only one of these actions. This bifunctional profile of activity may underlie the potent neuroprotective effects of AM-36 recently found in a stroke model in conscious rats.

Voltage-gated sodium channels as therapeutic targets

Voltage-gated sodium channels (VGSCs) play a central role in the generation and propagation of action potentials in neurons and other cells. VGSC modulators have their origins in empirical pharmacology and are being used as local anaesthetics, antiarrhythmics, analgesics and antiepileptics, and for other disorders. However, the identification of a multigene family of VGSCs, along with tools to study the different subtypes in pathophysiology, is now providing a rational basis for selective intervention. Recent advances have addressed the technical challenges of expressing and assaying these complex proteins, enabling the correlation of empirical pharmacology to subtypes and the screening of individual subtypes for novel inhibitors with increased potency and selectivity.

Role of sodium channel inhibition in neuroprotection: effect of vinpocetine

Vinpocetine (ethyl apovincaminate) discovered during the late 1960s has successfully been used in the treatment of central nervous system disorders of cerebrovascular origin for decades. The increase in the regional cerebral blood flow in response to vinpocetine administration is well established and strengthened by new diagnostical techniques (transcranial Doppler, near infrared spectroscopy, positron emission tomography). The latest in vitro studies have revealed the effect of the compound on Ca(2+)/calmodulin dependent cyclic guanosine monophosphate-phosphodiesterase 1, voltage-operated Ca(2+) channels, glutamate receptors and voltage dependent Na(+)-channels; the latest being especially relevant to the neuroprotective action of vinpocetine. The good brain penetration profile and heterogenous brain distribution pattern (mainly in the thalamus, basal ganglia and visual cortex) of labelled vinpocetin were demonstrated by positron emission tomography in primates and man. Multicentric, randomized, placebo-controlled clinical studies proved the efficacy of orally administered vinpocetin in patients with organic psychosyndrome. Recently positron emission tomography studies have proved that vinpocetine is able to redistribute regional cerebral blood flow and enhance glucose supply of brain tissue in ischemic post-stroke patients.

Betaxolol, a beta(1)-adrenoceptor antagonist, reduces Na(+) influx into cortical synaptosomes by direct interaction with Na(+) channels: comparison with other beta-adrenoceptor antagonists

Betaxolol, a beta(1)-adrenoceptor antagonist used for the treatment of glaucoma, is known to be neuroprotective in paradigms of ischaemia/excitotoxicity. In this study, we examined whether betaxolol and other beta-adrenoceptor antagonists interact directly with neurotoxin binding to sites 1 and 2 of the voltage-sensitive sodium channel (Na(+) channel) in rat cerebrocortical synaptosomes. Betaxolol inhibited specific [(3)H]-batrachotoxinin-A 20-alpha-benzoate ([(3)H]-BTX-B) binding to neurotoxin site 2 in a concentration-dependent manner with an IC(50) value of 9.8 microM. Comparison of all the beta-adrenoceptor antagonists tested revealed a potency order of propranolol>betaxolol approximately levobetaxolol>levobunolol approximately carteolol>/=timolol>atenolol. None of the drugs caused a significant inhibition of [(3)H]-saxitoxin binding to neurotoxin receptor site 1, even at concentrations as high as 250 microM. Saturation experiments showed that betaxolol increased the K(D) of [(3)H]-BTX-B binding but had no effect on the B(max). The association kinetics of [(3)H]-BTX-B were unaffected by betaxolol, but the drug significantly accelerated the dissociation rate of the radioligand. These findings argue for a competitive, indirect, allosteric mode of inhibition of [(3)H]-BTX-B binding by betaxolol. Betaxolol inhibited veratridine-stimulated Na(+) influx in rat cortical synaptosomes with an IC(50) value of 28. 3 microM. Carteolol, levobunolol, timolol and atenolol were significantly less effective than betaxolol at reducing veratridine-evoked Na(+) influx. The ability of betaxolol to interact with neurotoxin site 2 of the Na(+) channel and inhibit Na(+) influx may have a role in its neuroprotective action in paradigms of excitotoxicity/ischaemia and in its therapeutic effect in glaucoma.

Potent blockade of sodium channels and protection of brain tissue from ischemia by BIII 890 CL

We have synthesized a new benzomorphan derivative, 2R-[2alpha,3(S*), 6alpha]-1,2,3,4,5,6-hexahydro-6,11, 11-trimethyl-3-[2-(phenylmethoxy)propyl]-2, 6-methano-3-benzazocin-10-ol hydrochloride (BIII 890 CL), which displaced [(3)H]batrachotoxinin A-20alpha-benzoate from neurotoxin receptor site 2 of the Na(+) channel in rat brain synaptosomes (IC(50) = 49 nM), but exhibited only low affinity for 65 other receptors and ion channels. BIII 890 CL inhibited Na(+) channels in cells transfected with type IIA Na(+) channel alpha subunits and shifted steady-state inactivation curves to more negative potentials. The IC(50) value for the inactivated Na(+) channel was much lower (77 nM) than for Na(+) channels in the resting state (18 microM). Point mutations F1764A and Y1771A in transmembrane segment S6 in domain IV of the alpha subunit reduced the voltage- and frequency-dependent block, findings which suggest that BIII 890 CL binds to the local anesthetic receptor site in the pore. BIII 890 CL inhibited veratridine-induced glutamate release in brain slices, as well as glutamate release and neurotoxicity in cultured cortical neurons. BIII 890 CL (3-30 mg/kg s.c.) reduced lesion size in mice and rats when administered 5 min after permanent focal cerebral ischemia at doses that did not impair motor coordination. In contrast to many other agents, BIII 890 CL was neuroprotective in both cortical and subcortical regions of the rat brain. Our results demonstrate that BIII 890 CL is a potent, selective, and highly use-dependent Na(+) channel blocker that protects brain tissue from the deleterious effects of focal cerebral ischemia in rodents.