Neuroprotective properties of the uncompetitive NMDA receptor antagonist remacemide hydrochloride

Conantokin-G attenuates detrimental effects of NMDAR hyperactivity in an ischemic rat model of stroke

The neuroprotective activity of conantokin-G (con-G), a naturally occurring antagonist of N-methyl-D-aspartate receptors (NMDAR), was neurologically and histologically compared in the core and peri-infarct regions after ischemia/reperfusion brain injury in male Sprague-Dawley rats. The contralateral regions served as robust internal controls. Intrathecal injection of con-G, post-middle carotid artery occlusion (MCAO), caused a dramatic decrease in brain infarct size and swelling at 4 hr, compared to 26 hr, and significant recovery of neurological deficits was observed at 26 hr. Administration of con-G facilitated neuronal recovery in the peri-infarct regions as observed by decreased neurodegeneration and diminished calcium microdeposits at 4 hr and 26 hr. Intact Microtubule Associated Protein (MAP2) staining and neuronal cytoarchitecture was observed in the peri-infarct regions of con-G treated rats at both timepoints. Con-G restored localization of GluN1 and GluN2B subunits in the neuronal soma, but not that of GluN2A, which was perinuclear in the peri-infarct regions at 4 hr and 26 hr. This suggests that molecular targeting of the GluN2B subunit has potential for reducing detrimental consequences of ischemia. Overall, the data demonstrated that stroke-induced NMDAR excitoxicity is ameliorated by con-G-mediated repair of neurological and neuroarchitectural deficits, as well as by reconstituting neuronal localization of GluN1 and GluN2B subunits in the peri-infarct region of the stroked brain.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Long-term morphological and functional evaluation of the neuroprotective effects of post-ischemic treatment with melatonin in rats

Consensus on neuroprotection has pointed out the relevance of the long-term morphological and functional evaluation of the effectiveness of putative neuroprotective procedures. In the present study, place learning (Morris water maze) and working memory (eight-arm Olton radial maze) were evaluated in adult male rats 90 days after 15 min of global cerebral ischemia (four-vessel occlusion) followed by continuous i.v. infusion (10 mg/kg/hr) of melatonin (Isch + Mel) or vehicle (Isch + Veh) for 6 hr, and the pyramidal neuron population of the cornus Ammoni (CA) of the hippocampus and layers III and V of the medial prefrontal cortex was assessed at the end of the behavioral testing period (120 days after ischemia). Impairment of place learning, a significant delay in working memory acquisition, and a significant loss of pyramidal neurons in the Ammon's horn (CA1: 23%, CA2: 52% CA3: 73%, hilus: 64% remaining neurons), were observed in the Isch + Veh group. By contrast, a similar performance of the Isch + Mel group to that in the Intact and Sham groups and better than that of the Isch + Veh group, besides a significant reduction of pyramidal neuron loss in the CA subfields (CA1: 79%, CA2: 88% CA3: 86%, hilus: 72% remaining neurons), documented that melatonin treatment led to a long-term preservation of both the neural substrate, and the capability for integration of spatial learning and memory, mainly dependent on a normal hippocampal functioning. Overall the results emphasize the efficacy of melatonin in counteracting the pathophysiological processes induced by ischemia, by exerting its actions during a short but critical period early after the ischemic episode.

Effect of postnatal iron administration on MPTP-induced behavioral deficits and neurotoxicity: behavioral enhancement by L-Dopa-MK-801 co-administration

Two experiments were performed to investigate the interactive effects of postnatal iron administration and adult MPTP treatment upon the function of C57 Bl/6 mice tested at adult age and to ascertain the possible ameliatory effects of a subthreshold dose of L-Dopa co-administered with different doses of the uncompetitive glutamate antagonist, MK-801. Experiment I indicated that postnatal iron induced marked deficits (hypoactivity), initially, in all three parameters of motor activity at the 5.0 and 7.5 mg/kg doses, and to a lesser extent at the 2.5 mg/kg dose. Later combination with MPTP (2x40 mg/kg) potentiated severely these deficits. During the final period of testing a marked hyperactivity was obtained for the two higher dose groups; this effect was abolished in mice administered MPTP. Experiment II indicated that the deficits in motor activity parameters induced by postnatal iron at 7.5 mg/kg were alleviated in a dose-related manner by the co-administration of the uncompetitive glutamate antagonist, MK-801, with a subthreshold dose of L-Dopa. Postnatal iron (7.5 mg/kg) administration followed by low doses of MPTP (2x20 mg/kg) 3 months later virtually abolished all motor activity. The combination of these compounds increased also the motor activity of mice treated with MPTP (2x20 mg/kg) or mice treated with the combination of postnatal iron and MPTP. The combination of MK-801 with L-Dopa increased locomotor (0.3 mg/kg), rearing (0.1 and 0.3 mg/kg) and total activity (0.3 mg/kg) of iron-treated mice during the initial, hypoactive 30-min period of testing. Locomotor activity (0.1 mg/kg) of MPTP-treated mice was increased too during this period. During the final 30-min period of testing all three parameters of activity (locomotion, 0.3 mg/kg; rearing and total activity, 0.1 and 0.3 mg/kg) were enhanced in the iron-treated mice, locomotion (0.1 mg/kg) and rearing (0.1 mg/kg) in the iron plus MPTP treated mice and only locomotion (0.1 mg/kg) in the MPTP-treated mice. In control mice (vehicle+saline), the higher doses of MK-801 (0.1 and 0.3 mg/kg) enhanced both locomotor and total activity. Analyses of total iron concentration in the frontal cortex and basal ganglia of Fe(2+) and vehicle treated mice indicated that marked elevations basal ganglia iron levels of the 5.0 and 7.5 mg/kg groups, later injected either saline or MPTP, were obtained (Experiment I). In Experiment II, iron concentrations in the basal ganglia were elevated in both the Fe(2+)-sal and Fe(2+)-MPTP groups to 170 and 177% of Veh.-sal values, respectively. There was a significant increase in the frontal cortex of iron-treated mice later administered either saline or MPTP (2x40 mg/kg) in Experiment I as well as in those given iron followed by MPTP (2x20mg/kg) in Experiment II. The implications of iron overload in parkinsonism seem confirmed by the interactive effects of postnatal administration of the metal followed by adult MPTP treatment upon motor activity and the activity-enhancing effects of co-administration of L-Dopa with MK-801.

Pharmacological treatment of traumatic brain injury: a review of agents in development

Successful treatment strategies for patients with traumatic brain injury (TBI) remain elusive despite standardised clinical treatment guidelines, improved understanding of mechanisms of cellular response to trauma, and a decade of clinical trials aimed at identifying therapeutic agents targeted at mediators of secondary injury. The information explosion relative to mechanisms of secondary injury has identified several potential targets for intervention. Depending on the type of injury to the brain and the intensity and the success of resuscitation, necrosis, apoptosis, inflammatory and excitotoxic cellular damage can be seen. These same processes may continue postinjury, depending on the adequacy of clinical care. Each of these mechanisms of cellular damage can initiate a cascade of events mediated by endogenous signals that lead to secondary neurological injury. Several factors contributed to the failure of earlier clinical trials. Now that these have been recognised, a positive impact on future drug development in TBI has been realised. Both the US and Europe have organised brain injury consortiums where experts in the treatment of TBI provide insight into study design, implementation, conduct and oversight in conjunction with the pharmaceutical industry. Consequently, future clinical trials of new investigational treatments have greater potential for identifying therapies of merit in specific populations of patients with TBI. Pharmacological strategies under investigation are targeting sites involved in the secondary cascade that contribute to overall poor outcome following the primary injury. These treatments include ion channel antagonists including calcium channel antagonists, growth factors, antioxidants, stem cells, apoptosis inhibitors, and inhibitors of other signal modulators. In conclusion, the complexity of TBI pathology and the mechanisms contributing to secondary injury present unique therapeutic challenges. Appropriate research targets for intervention continue to be investigated, however, the likelihood of improving outcomes with a single approach is extremely small. There is a need for collaborative efforts to investigate the optimal time for drug administration and the logical sequence or combination of treatments that will ultimately lead to improved neurological outcomes in this population.

Co-administration of memantine and amantadine with sub/suprathreshold doses of L-Dopa restores motor behaviour of MPTP-treated mice

The antiparkinsonian effects of the uncompetitive NMDA antagonists, memantine, amantadine and MK-801, in combination with an acute subthreshold dose of L-Dopa (5 mg/kg) in drug-naive MPTP-treated mice or a suprathreshold dose (20 mg/kg) in L-Dopa tolerant MPTP-treated mice were investigated. In the former case, memantine (locomotion: 3 mg/kg; rearing: 1 mg/kg) and amantadine (locomotion and rearing: 10 mg/kg) injected 60 min before the subthreshold dose of L-Dopa (5 mg/kg), each induced an antiparkinsonian action in hypokinesic MPTP-treated mice that consisted of dose-specific, as opposed to dose-related, elevations of locomotion and rearing behaviour. At the same time, higher doses of memantine reduced further the rearing (10 and 30 mg/kg) and locomotor (30mg/kg) behaviour of the MPTP-treated mice. MK-801 plus L-Dopa elevated locomotion (0.1 mg/kg) but reduced rearing at the 0.3 mg/kg dose. In control, saline-treated mice, memantine (3, 10 and 30 mg/kg) and MK-801 (0.1 and 0.3 mg/kg) increased locomotor behaviour but decreased rearing behaviour, while amantadine produced no effects. Memantine increased locomotor (1 and 3 mg/kg, s.c.; 1 mg/kg dose restored activity) and rearing (0.3 and 3 mg/kg) activity in the L-Dopa tolerant MPTP-treated mice, whereas amantadine (3 and 10 mg/kg) restored both locomotor (30 mg/kg significantly increased locomotion but did not restore the activity level) and rearing (3 mg/kg only) activity. MK-801 (0.1 and 0.3 mg/kg, s.c.) also increased significantly locomotor activity of L-Dopa-tolerant MPTP mice although the antikinetic action was not reversed, thereby precluding a restorative effect of the compound. These results, demonstrating both a synergistic and a restorative effect of the NMDA antagonists in coadministration with L-Dopa, demonstrate a putative antiparkinson action by these compounds in a functional animal model that incorporates the "wearing-off" complications of L-Dopa administration in the disorder.

Drugs in development for social anxiety disorder: more to social anxiety than meets the SSRI

Individuals with social phobia (SP) fear and avoid a wide variety of social and performance situations in which they are exposed to unfamiliar persons or to possible scrutiny by others. The lifetime prevalence of SP is estimated to be as high as 13%. It is frequently co-morbid with and usually precedes the onset of other psychiatric illnesses and is associated with significant occupational and social impairment, including academic and vocational underachievement. Fortunately, there are effective treatments for this common and debilitating condition. There is currently considerable evidence for the efficacy of pharmacotherapy and especially the monoamine oxidase inhibitors (MAOIs) and selective serotonin re-uptake inhibitors (SSRIs) in the treatment of this disorder. However, SSRIs are generally preferred as the first-line treatment of choice due to the advantages of SSRIs over MAOIs in terms of safety and tolerability. Despite encouraging results, current treatments most often produce partial symptomatic improvement, rather than high end-state functioning. While current first line treatments for social phobia target the serotonergic system, it is important to remember that different social fears are likely to have different developmental roots and may be based on quite different neurobiological systems. In this article we provide a review of current pharmacotherapeutic options for SP, current knowledge of the neurobiology of SP, and a review of new and promising directions in pharmacological research. It is increasingly clear that serotonin (5-HT) is unlikely to be the whole story in SP and that other brain chemical systems, especially the dopaminergic, noradrenaline-corticotropin releasing hormone and gamma-aminobutyric acid (GABA) dependent systems, most probably have an important role to play in a substantial percentage of cases. A number of new and novel agents, including the substance P antagonists, GABA agonists and CRF antagonists show considerable promise in the treatment of SP. However, in order to enhance the understanding of the neurobiology and treatment response of SP, we need to develop more sophisticated theory-driven typologies of SP.

The low-affinity, use-dependent NMDA receptor antagonist AR-R 15896AR. An update of progress in stroke

Use-dependent N-methyl-D-aspartate (NMDA) receptor antagonists protect neurons from the lethal consequences of excessive stimulation by excitatory amino acids. Clinical development of high-affinity compounds such as MK801 have been limited due to untoward side effects. Toward this end, the lower-affinity use-dependent NMDA antagonists have greater margins of safety and have advanced to clinical trials for stroke, epilepsy, head trauma and chronic neurodegenerative disorders. AR-R 15896AR is currently in Phase II trials for stroke and has been repeatedly demonstrated to afford neuroprotection in a variety of in vivo and in vitro models associated with ischemia/excitotoxic conditions.

Ion channel modulation as the basis for neuroprotective action of MS-153

MS-153, (R)-(-)-5-methyl-1-nicotinoyl-2-pyrazoline, is a new neuroprotective drug. Recent data in the literature suggest that it inhibits glutamate accumulation occurring during ischemia and the translocation of protein kinase C gamma (PKC gamma). The present study was undertaken to prove the hypothesis that MS-153 blocks neuroreceptors and ion channels involved in glutamate accumulation. Neurons isolated from rat dorsal root ganglia and frontal cortex were used for recording channel currents by the whole-cell patch clamp technique. The effects of bath-applied MS-153 were examined on tetrodotoxin-sensitive and tetrodotoxin-resistant sodium channels and high voltage-gated calcium channels of dorsal root ganglion neurons, and channels activated by glutamate, N-methyl-D-aspartate (NMDA), kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxarole propionic acid (AMPA), gamma-aminobutyric acid (GABA) and acetylcholine (ACh) in cortical neurons. MS-153 at a concentration of 300 microM had no effect on either tetrodotoxin-sensitive or tetrodotoxin-resistant sodium channels. High voltage-gated calcium channels were either suppressed or not affected by 1-300 microM MS-153. The variable blocking effect of MS-153 was due to the variable activity of intracellular components in individual neurons, especially that of PKC, whose translocation is known to be inhibited by MS-153. When 100 nM phorbol 12-myristate-13-acetate (PMA) was applied to neurons, MS-153 suppressed the calcium channel current more frequently. Calphostin C (0.5 microM), a specific PKC inhibitor, applied intracellularly via recording patch pipette, completely abolished MS-153 suppression of the calcium channel current. Currents induced by glutamate, NMDA, kainate, AMPA, GABA or ACh were not affected by MS-153 at 300 microM. It was concluded that MS-153 inhibited high voltage-gated calcium channels through interactions with PKC, thereby preventing massive release of glutamate from nerve terminals in ischemic conditions.

Restoration and putative protection in Parkinsonism

Synergistic antiparkinsonian actions of different classes of putative therapeutic agents co-administered with a subthreshold dose of L-3,4-dihydroxyphenylalanine (L-Dopa) (5 mg/kg) in drug-naive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice as well as the restorative actions of those compounds in suprathreshold L-Dopa-tolerant MPTP-treated mice subjected to "wearing-off" of L-Dopa efficacy were assessed in a series of experiments. The classes of compounds studied included the noncompetitive NMDA antagonists, memantine, amantadine and MK-801, the anticonvulsive and putative anticonvulsive agents, lamotrigine, FCE 26743, phenytoin, the monoamine oxidase inhibitors, L-Deprenyl, amiflamine, alpha-ethyltryptamine, clorgyline and guanfacine. In this final case, the restorative effects of clonidine and guanfacine were antagonized by the alpha(2)-adrenoceptor antagonist, yohimbine, but not the alpha(1)-adrenoceptor antagonist, prazosin. Within each class of potentially therapeutic agents a differential restorative efficacy was obtained, but the combination of different doses of apomorphine with clonidine failed to restore motor activity. Finally, the neuroprotective actions of acute and subchronic administration of the nitrone spin-trapping compound, alpha-phenyl-tert-butyl nitrone upon the spontaneous motor behaviour and striatal dopamine concentrations of MPTP-treated mice was examined.

New anti-epileptic drugs

Epilepsy represents the most common serious neurological disorder, with a prevalence of 0.4 - 1%. Approximately 30% of patients are resistant to currently available drugs. New anti-epileptic drugs are needed to treat refractory epilepsy, improve upon current therapies, improve the prognosis of epilepsy and to prevent the epileptogenic process. Designing compounds with specific physiological targets would seem the most rational method of anti-epileptic drug development, but results from this approach have been disappointing; the widespread screening of compounds in animal models has been much more fruitful. Older methods of animal screening have used acute seizure models, which bear scant relationship to the human condition. More modern methods have included the development of animal models of chronic epilepsy; although more expensive, it is likely that these models will be more sensitive and more specific in determining anti-epileptic efficacy. In this review, we consider the possible physiological targets for anti-epileptic drugs, the animal models of epilepsy, problems with clinical trials and ten promising anti-epileptic drugs in development (AWD 131-138, DP16 (DP-VPA), ganaxolone, levetiracetam, losigamone, pregabalin, remacemide, retigabine, rufinamide and soretolide). Perhaps the most important advances will come about from the realisation that epilepsy is a symptom, not a disease. Preclinical testing should be used to determine the spectrum of epilepsies that a drug can treat, and to direct later clinical trials, which need to select patients based on carefully defined epilepsy syndromes and aetiologies. Not only will such an approach improve the sensitivity of clinical trials, but also will lead to a more rational basis on which to treat.

Neuroprotective effect of remacemide hydrochloride in a perforant pathway stimulation model of status epilepticus in the rat

Previous studies have demonstrated that remacemide and its desglycinyl metabolite, AR-R 2495AA, reduce neuronal damage in animal models of ischemia, subarachnoid hemorrhage, and traumatic brain injury. The aim of the present study was to investigate whether remacemide hydrochloride also alleviates seizure-induced neuronal damage in a model of status epilepticus induced by the stimulation of the perforant pathway (PP) in the rat. Chronic oral remacemide treatment (3 x 25 mg/kg/day) was started either 2 days before or 2 h after the beginning of PP stimulation (2 mA, 20 Hz, 0.1 ms pulse duration for 60 min). The effects of remacemide treatment on the severity of seizures, electroencephalogram (EEG) parameters, seizure-induced neuronal damage in the temporal lobe regions, and memory impairment were compared to unstimulated and stimulated vehicle-treated controls, and carbamazepine-pre-treated (3 x 40 mg/kg/day) rats. Both remacemide and carbamazepine pretreatments, but not remacemide posttreatment, decreased pyramidal cell damage in the CA3 and CA1 subregions of the hippocampus (P < 0.05). In addition, overall neuronal damage in the extrahippocampal temporal lobe regions (the piriform cortex, entorhinal cortex, and the amygdaloid complex) was milder in remacemide-pretreated rats compared to stimulated control rats (P < 0.01). The neuroprotective effect was most evident on the side contralateral to stimulation. Remacemide or carbamazepine pretreatment had no evident effect on the number or duration of behavioral seizures during PP stimulation. Neither drug altered the spectral parameters of the baseline EEG or prevented status epilepticus-induced EEG slowing observed 2 weeks after PP stimulation. Nor did remacemide or carbamazepine treatment alleviate spatial memory impairment determined in a Morris water-maze task 2 weeks after PP stimulation. Our data provide evidence that pretreatment with remacemide has a moderate neuroprotective effect against status epilepticus-induced neuronal damage.

New developments in managing transient ischemic attack and acute stroke

During this decade, which has been designated the decade of the brain, the event of transient ischemic attack (TIA) or acute ischemic stroke is considered a brain attack requiring rapid diagnosis and treatment. This increased focus on the clinical problems of TIA and stroke has resulted in rapid advances in management of this patient population. This article will highlight for critical care nurses some of the many advances in patient management of TIA and stroke that have occurred in the past few years. Advances in the areas of diagnostic studies, pharmacologic interventions, and nursing care will be covered. Furthermore, some of the new developments on the horizon will be summarized.

Clinical potential for the use of neuroprotective agents. A brief overview

"Stroke treatment seems to be entering a golden age ...." Fisher's observation not only applies to ischemic stroke, but to all the conditions described above, and in the future, possibly (and quite speculatively), to other neurologic diseases, such as multiple sclerosis, amyotrophic lateral sclerosis, even radiation therapy and Bell's palsy. Physicians must sharpen their criteria for decisions regarding therapy and must" ... be prepared to accept what is actually known from scientific data ... rather than to rely on instinct, clinical impression, or the need to do something rather than nothing."