Is pharmacological neuroprotection dependent on reduced glutamate release?

Traditional and Innovative Anti-seizure Medications Targeting Key Physiopathological Mechanisms: Focus on Neurodevelopment and Neurodegeneration

Despite the wide range of compounds currently available to treat epilepsy, there is still no drug that directly tackles the physiopathological mechanisms underlying its development. Indeed, antiseizure medications attempt to prevent seizures but are inefficacious in counteracting or rescuing the physiopathological phenomena that underlie their onset and recurrence, and hence do not cure epilepsy. Classically, the altered excitation/inhibition balance is postulated as the mechanism underlying epileptogenesis and seizure generation. This oversimplification, however, does not account for deficits in homeostatic plasticity resulting from either insufficient or excessive compensatory mechanisms in response to a change in network activity. In this respect, both neurodevelopmental epilepsies and those associated with neurodegeneration may share common underlying mechanisms that still need to be fully elucidated. The understanding of these molecular mechanisms shed light on the identification of new classes of drugs able not only to suppress seizures, but also to present potential antiepileptogenic effects or "disease-modifying" properties.

Selective adenosine A2A receptor inhibitor SCH58261 reduces oligodendrocyte loss upon brain injury in young rats

Cellular elements of maturing brain are vulnerable to insults, which lead to neurodevelopmental defects. There are no established treatments at present. Here we examined the efficacy of selective adenosine A_2A receptor inhibitor SCH58261 to combat brain injury, particularly oligodendrocyte (OL) lineage cells, in young rats. Wistar rats (n = 24, 6.5 days old) were randomly divided into equal groups of four. The sham (SHAM) group received no treatment, the vehicle (VEHICLE) group received 0.1% dimethylsufoxide, the injury (INJ) group was exposed to oxygen-glucose deprivation insult, and the injury+SCH58261 (INJ+SCH58261) group was exposed to the insult and received 1 μM SCH58261. Immunocytochemical experiments revealed that there was a significant reduction in the populations of mature OL (MBP⁺ OLs) and immature OL precursors (NG2⁺ OPCs) in the INJ group compared to SHAM group. Furthermore, there was also a significant increase in the percent of apoptotic MBP⁺ OL and NG2⁺ OPC populations as evidenced by TUNEL assay. In addition, there was a significant reduction in the proliferation rate among NG2⁺ OPCs, which was confirmed by BrdU immunostaining. On the other hand, treatment with SCH58261 significantly enhanced survival, evidenced by the reduction in apoptotic indices for both cell types, and it is preserved the NG2⁺ OPC proliferation. Activation of adenosine A_2A receptors may contribute to OL lineage cell loss in association with decreased mitotic behavior of OPCs in neonatal brains upon injury. Future investigations assessing ability of SCH58261 to regenerate myelin will provide insights into its wider clinical relevance.

Development, Characterization, and in-vivo Pharmacokinetic Study of Lamotrigine Solid Self-Nanoemulsifying Drug Delivery System

Purpose

This study aimed to prepare solid self-nanoemulsified drug delivery system (S-SNEDDS) of lamotrigine (LMG) for enhancing its dissolution and oral bioavailability (BA).

Methods

Nineteen liquid SNEDDS were prepared (R1-R19) using D-optimal design with different ratios of oil, surfactant (S), and cosurfactant (Cos). The formulations were characterized regarding robustness to dilution, droplet size, thermodynamic stability testing, self-emulsification time, in-vitro release in 0.1 N HCl and phosphate buffer (PB; pH 6.8). Design Expert^® 11 software was used to select the optimum formulations. Eight S-SNEDDS were prepared (S1-S8) using 2³ factorial design, and characterized by differential scanning calorimetry (DSC), powder x-ray diffraction (PXRD), and scanning electron microscopy (SEM). The optimum formulation was chosen regarding in-vitro drug released in 0.1 N HCl and PB, compared to pure LMG and commercial tablet (Lamictal^®). The BA of LMG from the optimized S-SNEDDS formulation was evaluated in rabbits compared to pure LMG and Lamictal^®.

Results

The optimized S-SNEDDS was S2, consisting of R9 adsorbed on Aeroperl^® 300 in a ratio of 1:1, with the best results regarding in-vitro drug released in 0.1 N HCl at 15 min (100%) compared to pure LMG (73.40%) and Lamictal^® (79.43%), and in-vitro drug released in PB at 45 min (100%) compared to pure LMG (30.46%) and Lamictal^® (92.08%). DSC, PXRD, and SEM indicated that LMG was molecularly dispersed within the solid nano-system. The BA of S2 was increased 2.03 and 1.605 folds compared to pure LMG, and Lamictal^®, respectively.

Conclusion

S2 is a promising S-SNEDDS formulation. It can be a potential carrier for improving dissolution, and BA of LMG.

Low doses of Perampanel protect striatal and hippocampal neurons against in vitro ischemia by reversing the ischemia-induced alteration of AMPA receptor subunit composition

Energy depletion caused by ischemic brain insults may result in persistent neuronal depolarization accompanied by hyper-stimulation of ionotropic glutamate receptors and excitotoxic phenomena, possibly leading to cell death. The use of glutamate receptor antagonists, such as the AMPARs antagonist Perampanel (PER), might be a pharmacological approach to counteract the excessive over-activation of glutamate receptors providing neuroprotective effects. Using electrophysiological and molecular analyses, we investigated the effect of PER against in vitro ischemia obtained by oxygen and glucose deprivation (OGD) in rat slices of two brain structures particularly sensitive to ischemic insults, the nucleus striatum and the hippocampus. We found that in these regions PER was able to avoid the OGD-induced neuronal suffering, at low doses not reducing basal excitatory synaptic transmission and not altering long-term potentiation (LTP) induction. Furthermore, in both the analysed regions, PER blocked a pathological form of LTP, namely ischemic LTP (iLTP). Finally, we hypothesized that the protective effect of PER against OGD was due to its capability to normalize the altered synaptic localization and function of AMPAR subunits, occuring after an ischemic insult. Taken together these findings support the idea that PER is a drug potentially effective to counteract ischemic damage.

High-resolution metabolomics study revealing l-homocysteine sulfinic acid, cysteic acid, and carnitine as novel biomarkers for high acute myocardial infarction risk

BACKGROUND

Identifying changes in serum metabolites before the occurrence of acute myocardial infarction (AMI) is an important approach for finding novel biomarkers of AMI.

METHODS

In this prospective cohort study, serum samples obtained from patients at risk of AMI (n = 112) and non-risk controls (n = 89) were tested using high-resolution metabolomics (HRM). Partial least-squares discriminant analysis (PLS-DA), along with univariate analysis using a false discovery rate (FDR) of q = 0.05 were performed to discriminate metabolic profiles and to determine significantly different metabolites between healthy control and AMI risk groups.

RESULTS

PLS-DA significantly separated the AMI risk sera from control sera. The metabolites associated with amino acid biosynthesis, 2-oxocarboxylic acid, tryptophan, and amino sugar and nucleotide sugar metabolism pathways were mainly elevated in patients at risk of AMI. Further validation and quantification by MS/MS showed that tryptophan, carnitine, L-homocysteine sulfinic acid (L-HCSA), and cysteic acid (CA) were upregulated, while L-cysteine and L-cysteine sulfinic acid (L-CSA) were downregulated, specifically among AMI risk sera. Additionally, these discriminant metabolic profiles were not related to hypertension, smoking or alcoholism.

CONCLUSION

In conclusion, detecting upregulated L-HCSA and CA along with carnitine among patients at risk for AMI could serve as promising non-invasive biomarkers for early AMI detection.

The retinoprotective role of phenytoin

Phenytoin is a non-sedative barbiturate derivate and has been recently rediscovered as a neuroprotective and retinoprotective compound in patients affected by optic neuritis secondary to multiple sclerosis. However, currently there are still no neuroprotective compounds registered and available in the clinic. We reviewed the literature supporting the retinoprotective properties of phenytoin and analyzed the various approaches and definitions from the first research periods onwards. The retinoprotective role of phenytoin was already known in the 1970s, but only recently has this effect been rediscovered, confirming that it could indeed provide structural protection of the retinal cells.

Lacosamide protects striatal and hippocampal neurons from in vitro ischemia without altering physiological synaptic plasticity

Lacosamide ([(R)-2-acetamido-N-benzyl-3-methoxypropanamide], LCM), is an antiepileptic that exerts anticonvulsant activity by selectively enhancing slow sodium channel inactivation. By inhibiting seizures and neuronal excitability it might therefore be a good candidate to stabilize neurons and protect them from energetic insults. Using electrophysiological analyses, we have investigated in mice the possible neuroprotective effect of LCM against in vitro ischemia obtained by oxygen and glucose deprivation (ODG), in striatal and hippocampal tissues, two brain structures particularly susceptible to ischemic injury and of pivotal importance for different form of learning and memory. We also explored in these regions the influence of LCM on firing discharge and on long-term synaptic plasticity. We found that in both areas LCM reduced the neuronal firing activity in a use-dependent manner without influencing the physiological synaptic transmission, confirming its anticonvulsant effects. Moreover, we found that this AED is able to protect, in a dose dependent manner, striatal and hippocampal neurons from energy metabolism failure produced by OGD. This neuroprotective effect does not imply impairment of long-term potentiation of striatal and hippocampal synapses and suggests that LCM might exert additional beneficial therapeutic effects beyond its use as antiepileptic.

Glutamate drugs and pharmacogenetics of OCD: a pathway-based exploratory approach

INTRODUCTION

Neuropharmacology research in glutamate-modulating drugs supports their development and use in the management of neuropsychiatric disorders, including major depression, Alzheimer's disorder and schizophrenia. Concomitantly, there is a growing use of these agents used in the treatment of obsessive-compulsive disorder (OCD).

AREAS COVERED

This article provides a review of glutamate-modulating drugs used in the treatment of OCD. Specifically, the authors examine riluzole, N-acetylcysteine, d-cycloserine, glycine, ketamine, memantine and acamprosate as treatments. Furthermore, recent genetic epidemiology research findings are presented with a focus on the positional candidate genes SLC1A1 (a glutamate transporter), ADAR3 (an RNA-editing enzyme), RYR3 (a Ca(2+) channel), PBX1 (a homeobox transcription factor) and a GWAS candidate gene, DLGAP1 (a protein interacting with post-synaptic density). These genetic findings are submitted to a curated bioinformatics database to conform a biological network for discerning potential pharmacological targets.

EXPERT OPINION

In the genetically informed network, known genes and identified key connecting components, including DLG4 (a developmental gene), PSD-95 (a synaptic scaffolding protein) and PSEN1 (presenilin, a regulator of secretase), conform a group of potential pharmacological targets. These potential targets can be explored, in the future, to deliver new therapeutic approaches to OCD. There is also the need to develop a better understanding of neuroprotective mechanisms as a foundation for future OCD drug discovery.

Neuroprotective effects of the mood stabilizer lamotrigine against glutamate excitotoxicity: roles of chromatin remodelling and Bcl-2 induction

Lamotrigine (LTG), a phenyltriazine derivative and anti-epileptic drug, has emerged as an effective first-line treatment for bipolar mood disorder. Like the other mood stabilizers lithium and valproate, LTG also has neuroprotective properties but its exact mechanisms remain poorly defined. The present study utilized rat cerebellar granule cells (CGCs) to examine the neuroprotective effects of LTG against glutamate-induced excitotoxicity and to investigate potential underlying mechanisms. CGCs pretreated with LTG were challenged with an excitotoxic dose of glutamate. Pretreatment caused a time- and concentration-dependent inhibition of glutamate excitotoxicity with nearly full protection at higher doses (≥ 100 μm), as revealed by cell viability assays and morphology. LTG treatment increased levels of acetylated histone H3 and H4 as well as dose- and time-dependently enhanced B-cell lymphoma-2 (Bcl-2) mRNA and protein levels; these changes were associated with up-regulation of the histone acetylation and activity of the Bcl-2 promoter. Importantly, lentiviral-mediated Bcl-2 silencing by shRNA reduced both LTG-induced Bcl-2 mRNA up-regulation and neuroprotection against glutamate excitotoxicity. Finally, the co-presence of a sub-effective concentration of LTG (10 μm) with lithium or valproate produced synergistic neuroprotection. Together, our results demonstrate that the neuroprotective effects of LTG against glutamate excitotoxicity likely involve histone deacetylase inhibition and downstream up-regulation of anti-apoptotic protein Bcl-2. These underlying mechanisms may contribute to the clinical efficacy of LTG in treating bipolar disorder and warrant further investigation.

Gabapentin decreases epileptiform discharges in a chronic model of neocortical trauma

Gabapentin (GBP) is an anticonvulsant that acts at the α2δ-1 submit of the L-type calcium channel. It is recently reported that GBP is a potent inhibitor of thrombospondin (TSP)-induced excitatory synapse formation in vitro and in vivo. Here we studied effects of chronic GBP administration on epileptogenesis in the partial cortical isolation ("undercut") model of posttraumatic epilepsy, in which abnormal axonal sprouting and aberrant synaptogenesis contribute to occurrence of epileptiform discharges. Results showed that 1) the incidence of evoked epileptiform discharges in undercut cortical slices studied 1 day or ~2 weeks after the last GBP dose, was significantly reduced by GBP treatments, beginning on the day of injury; 2) the expression of GFAP and TSP1 protein, as well as the number of FJC stained cells was decreased in GBP treated undercut animals; 3) in vivo GBP treatment of rats with undercuts for 3 or 7 days decreased the density of vGlut1-PSD95 close appositions (presumed synapses) in comparison to saline treated controls with similar lesions;4) the electrophysiological data are compatible with the above anatomical changes, showing decreases in mEPSC and sEPSC frequency in the GBP treated animals. These results indicate that chronic administration of GBP after cortical injury is antiepileptogenic in the undercut model of post-traumatic epilepsy, perhaps by both neuroprotective actions and decreases in excitatory synapse formation. The findings may suggest the potential use of GBP as an antiepileptogenic agent following traumatic brain injury.

Maximizing neuroprotection: where do we stand?

Brain and spinal cord traumas include blunt and penetrating trauma, disease, and required surgery. Such traumas trigger events such as inflammation, infiltration of inflammatory and other cells, oxidative stress, acidification, excitotoxicity, ischemia, and the loss of calcium homeostasis, all of which cause neurotoxicity and neuron death. To prevent trauma-induced neurological deficits and death, each of the many neurotoxic events that occur in parallel or sequentially must be minimized or prevented. Although neuroprotective techniques have been developed that block single neurotoxic events, most provide only limited neuroprotection and are only applied singly. However, because many neurotoxicity triggers arise from common events, an approach for invoking more effective neuroprotection is to apply multiple neuroprotective methods simultaneously before the many neurotoxic triggers and cascades are initiated and become irreversible. This paper first discusses some triggers of neurotoxicity and neuroprotective mechanisms that block them, including hypothermia, alkalinization, and the administration of adenosine. It then examines how the simultaneous application of these techniques provides significantly greater neuroprotection than is provided by any technique alone. The paper also stresses the importance of determining whether the neuroprotection provided by these techniques can be further enhanced by combining them with additional techniques, such as the systemic administration of glucocorticoids. Finally, the paper stresses the absolute critical importance of applying these techniques within the "golden hour" following trauma, before the many neurotoxic events and cascades are manifest and before the neurotoxic cascades become irreversible.

Neuroprotection of lamotrigine on hypoxic-ischemic brain damage in neonatal rats: Relations to administration time and doses

Lamotrigine (LTG), an antiepileptic drug, has been shown to be able to improve cerebral ischemic damage by limiting the presynaptic release of glutamate. The present study investigated further the neuroprotective effect of LTG on hypoxic-ischemic brain damage (HIBD) in neonatal rats and its relations to administration time and doses. The HIBD model was produced in 7-days old SD rats by left common carotid artery ligation followed by 2 h hypoxic exposure (8% oxygen). LTG was administered intraperitoneally with the doses of 5, 10, 20, and 40 mg/kg 3 h after operation and the dose of 20 mg/kg 1 h before and 3 h, 6 h after operation. Blood and brain were sampled 24 h after operation. Nissl staining, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL), and neuron-specific enolase (NSE) immunohistochemical staining were used for morphological studies. Water content in left cortex and NSE concentration in serum were determined. LTG significantly reduced water content in the cerebral cortex, as well as the number of TUNEL staining neurons in the dentate gyrus and cortex in hypoxic-ischemia (HI) model. Furthermore, LTG significantly decreased the NSE level in serum and increased the number of NSE staining neurons in the cortex. These effects, except that on water content, were dose-dependent and were more remarkable in the pre-treated group than in the post-treated groups. These results demonstrate that LTG may have a neuroprotective effect on acute HIBD in neonates. The effect is more prominent when administrated with higher doses and before HI.

Glutamate release predicts ongoing myocardial ischemia of rat hearts

BACKGROUND

Glutamate metabolism is associated with myocardial ischemia-reperfusion, but it is not clear whether glutamate reveals ongoing ischemia (OI). We evaluated whether microdialysis would detect OI induced by coronary artery ligation in a rat cardiac transplantation model.

MATERIAL AND METHODS

A total of 24 Fischer 344 rats underwent syngeneic heterotopic cardiac transplantation. Of these, 16 rats underwent ligation of the left anterior coronary artery (LAD) of the heart to induce ongoing ischemia (OI), of which eight grafts received intra-aortally Gabapentin (12 mg/graft), a glutamate-release inhibitor and eight grafts with transplantation only served as the control. With a microdialysis catheter samples for glucose, lactate, pyruvate, glutamate, and glycerol were analysed spectrophotometrically. Histology and aquaporin 7 evaluations were performed after graft harvesting.

RESULTS

Glutamate was elevated after 15 min of reperfusion in OI as compared with Control (14.31 +/- 5.03 microM vs 6.75 +/- 2.21 microM, p = 0.05), respectively. Glycerol remained high in OI (61.89 +/- 46.13 microM to 15.84 +/- 0.85 microM, p = ns) and low in Control (12.33 +/- 3.36 microM to 5.52 +/- 0.25 microM, p = ns). Gabapentin decreased glutamate release from 7.32 +/- 1.57 microM to 2.71 +/- 0.64 microM, (p < 0.05) and resulted in decrease of glycerol levels from 24.64 +/- 4.03 microM to 10.43 +/- 2.49 microM, (p < 0.05) in OI. The expression of aquaporin 7 and histology confirmed OI.

CONCLUSIONS

We suggest that glutamate release may be used as an early indicator of OI after cardiac arrest.

N-ethyl lidocaine (QX-314) protects striatal neurons against ischemia: an in vitro electrophysiological study

In this study, we have investigated the neuroprotective actions of the membrane impermeable, lidocaine analog, N-ethyl lidocaine (QX-314) in the striatum. The effects of this drug were compared with those caused by the strictly-related-compound and sodium channel blocker lidocaine. To address this issue, electrophysiological recordings were performed in striatal slices, in control condition (normoxia) and during combined oxygen and glucose deprivation (in vitro ischemia). Either QX-314 or lidocaine induced, to some extent, a protection of the permanent electrophysiological alteration (field potential loss) caused by a period (12 min) of ischemia. Thus, both compounds permitted a partial recovery of the ischemic depression of the corticostriatal transmission and reduced the amplitude of the ischemic depolarization in medium spiny neurons. However, while QX-314, at the effective concentration of 100 microM, slightly reduced the amplitude of the excitatory field potential and did not affect the current-evoked spikes discharge of medium spiny striatal neurons, equimolar lidocaine depressed the field potential and eliminated repetitive spikes on a depolarizing step. On the basis of these observations, our results suggest the use of QX-314 as a neuroprotective agent in ischemic brain disorders.

Effect of combined ultrasound and microbubbles treatment in an experimental model of cerebral ischemia

Combined 2-MHz ultrasound (US) and second-generation, sulfur hexafluoride microbubbles (MB) treatment (US+MB) was performed in a permanent middle cerebral artery (MCA) occlusion model in rats to evaluate possible effects on the ischemic cascade. We used 16 Wistar rats and the MCA occlusion model for stroke induction. Glutamate, pyruvate, lactate and glycerol levels were measured by intracerebral microdialysis before and after stroke induction and after US+MB application (n = 8) for 20 h. After 24 h, brain infarct volume, apoptosis and IL-6 and TNF-alpha levels were evaluated. The infarct volume was significantly reduced (p < 0.05) in the US+MB-treated group compared with control animals. In additional, glutamate levels were significantly lower in US+MB-treated animals, and these animals showed a higher rate of apoptotic cell death in the infarcted area. The levels of IL-6 and TNF-alpha concentrations were not different in both groups, and there was no apoptotic cell death outside the infarction in animals treated with US+MB. The results demonstrate that US+MB with second generation microbubbles does not have a harmful effect on ischemic stroke in an MCA occlusion model of the rat.

Neuroprotection by lamotrigine in a rat model of neonatal hypoxic-ischaemic encephalopathy

Hypoxic-ischaemic (HI) encephalopathy is a severe complication of perinatal asphyxia and remains a frequent cause of a variety of brain disorders with long-term effects on the patients' life. The associated brain damage is strongly related to the toxic action of excitatory amino acids, especially glutamate and aspartate. Lamotrigine is an anti-epileptic drug that blocks the voltage-gated sodium channels of the presynaptic neuron and inhibits the release of glutamate. In the present study a well-established model of perinatal asphyxia in 7-d-old rats was used to investigate the effect of lamotrigine on HI-induced damage to different hippocampal brain structures, since disruption of this brain area is thought to play a key role in schizophrenia and epilepsy. Therefore, a combination of ischaemia, induced by unilateral occlusion of the left common carotid artery, followed by exposure to a 1-h period of hypoxia, was carried out in neonatal 7-d-old rats. Immediately after the insult, lamotrigine was given i.p. The histological outcome in the hippocampus was conducted and the tissue levels of glutamate, aspartate, GABA, and glutamine in the same area were determined. A remarkable reduction of HI-evoked damaged neurons in most of the investigated hippocampal regions was noted after lamotrigine administration. Furthermore, lamotrigine decreased the asphyxia-induced hippocampal tissue levels of glutamate and aspartate. Immediately after perinatal asphyxia GABA levels were enhanced, while levels of glutamine were decreased. Lamotrigine administration did not affect either GABA or glutamine levels. These results suggest a neuroprotective effect of lamotrigine in this particular animal model of neonatal HI encephalopathy.

Memantine reduces neuronal dysfunctions triggered by in vitro ischemia and 3-nitropropionic acid

Memantine, a low-affinity uncompetitive NMDA receptor antagonist, has been widely utilized for the treatment of Alzheimer's disease. A possible neuroprotective role of this drug in pathophysiological conditions involving an altered energetic metabolism of the basal ganglia has never been addressed. Thus, we have characterized the electrophysiological effect of memantine on striatal spiny neurons recorded under control conditions and after in vitro ischemia (oxygen and glucose deprivation). Memantine reduced in a dose-dependent manner (EC(50)=5 microM) the irreversible loss of field potential amplitude induced by in vitro ischemia. The neuroprotective effect of memantine against in vitro ischemia was even more potent (EC(50)=3.2 microM) in the absence of external magnesium, a condition enhancing NMDA-mediated glutamatergic transmission. Memantine was also able to block long-term potentiation recorded from spiny neurons following a brief ischemic episode. Moreover, memantine showed protection against irreversible field potential loss induced by 3-nitropropionic acid (3-NP), an inhibitor of the mitochondrial complex II, without influencing toxicity induced by rotenone, a complex I inhibitor. Memantine could represent a potential neuroprotective agent in pathophysiological conditions involving an altered energy metabolism of basal ganglia.

Effect of the L- or D-aspartate on ecto-5'nucleotidase activity and on cellular viability in cultured neurons: participation of the adenosine A(2A) receptors

Glutamate increases the extracellular adenosine levels, an important endogenous neuromodulator. The neurotoxicity induced by glutamate increases the ecto-5'-nucleotidase activity in neurons, which produces adenosine from AMP. L- and D-aspartate (Asp) mimic most of the actions of glutamate in the N-methyl-D-aspartate (NMDA) receptors. In the present study, both amino acids stimulated the ecto-5'-nucleotidase activity in cerebellar granule cells. MK-801 and AP-5 prevented the L- and D-Asp-evoked activation of ecto-5'-nucleotidase. Both NMDA receptor antagonists prevented completely the damage induced by L-Asp, but partially the D-Asp-induced damage. The antagonist of adenosine A(2A) receptors (ZM 241385) prevented totally the L- Asp-induced cellular death, but partially the neurotoxicity induced by D-Asp and the antagonist of adenosine A(1) receptors (CPT) had no effect. The results indicated a different involvement of NMDA receptors on the L- or D-Asp-evoked activation of ecto-5'-nucleotidase and on cellular damage. The adenosine formed from ecto-5'-nucleotidase stimulation preferentially acted on adenosine A(2A) receptor which is probably co-operating with the neurotoxicity induced by amino acids.

A microdialysis study of effects of gastrodin on neurochemical changes in the ischemic/reperfused rat cerebral hippocampus

Gastrodin is a component extracted from the rhizome of Gastrodia elata, and has been shown to possess protective effects against neuron damage induced by simulated cerebral ischemia in previous studies. But its neurochemical effects on the ischemic brain had not been well studied. The present study aimed at evaluating the effects of gastrodin on the changes of transmitter amino acids in rat hippocampus during cerebral ischemia/reperfusion. Microdialysis sampling was performed during ischemia and early reperfusion periods in rats, and the glutamate and gamma-aminobutyric acid (GABA) in the dialysate were measured using high-performance liquid chromatography (HPLC). Administration of gastrodin (100 mg/kg) before ischemia significantly reduced the ischemia-induced elevation of glutamate levels during the postischemic period, increased the rise of extracellular GABA during the reperfusion periods, thus decreased the glutamate/GABA ratios during ischemia and reperfusion. These results provide insights to explain the neurochemical effects of gastrodin when applied prior to an ischemic event.

The phospholipid mediator platelet-activating factor mediates striatal synaptic facilitation

The phospholipid mediator platelet-activating factor (PAF), an endogenous modulator of glutamatergic neurotransmission, can also be secreted by brain mononuclear phagocytes during HIV-1 infection. Platelet-activating factor can induce neuronal apoptosis by NMDA receptor-dependent and independent mechanisms. We now demonstrate that acute administration of sublethal doses of PAF to striatal slices augments synaptic facilitation in striatal neurons following high-frequency stimulation, which can be blocked by PAF receptor antagonists, suggesting that striatal synaptic facilitation can be augmented by PAF receptor agonism. We also demonstrate that repeated sublethal doses of PAF during tetanic stimulation can greatly increase the magnitude of postsynaptic potentials and action potentials, but a lethal dose of PAF destroys the capacity of corticostriatal synapses to achieve this augmented synaptic facilitation. Thus, the relative concentration and temporal pattern of PAF expression at glutamatergic synapses may govern whether it acts in a physiologic or pathophysiologic manner during striatal neurotransmission.

A comparison of the glutamate release inhibition and anti-allodynic effects of gabapentin, lamotrigine, and riluzole in a model of neuropathic pain

The effects of treatment with the anti-convulsant agents, lamotrigine and riluzole were compared with gabapentin in a rat experimental model of neuropathic pain. Rats were treated intraperitoneally, with gabapentin (30, 100 and 300 mg/kg), lamotrigine (2, 10 and 50 mg/kg) or riluzole (6 and 12 mg/kg) prior to, and every 12 h for 4 days following chronic constriction injury (CCI) of the sciatic nerve. Mechanical and cold sensitivity were assessed prior to surgery (baseline) and then at 4, 8 and 12 days following CCI. The four-day treatment with each of the agents was effective at producing reductions in the development of mechanical and cold hypersensitivity for periods ranging from the fourth to 12th day. The highest doses of each of the agents were also assessed on formalin-induced nociceptive behaviors and on formalin-induced increases in extracellular glutamate (Glu) and aspartate (Asp) in the spinal cord dorsal horn (SCDH) of awake behaving rats using in vivo microdialysis. Nociceptive scores in formalin test were significantly decreased by gabapentin (300 mg/kg i.p.) and riluzole (12 mg/kg i.p.), but not by lamotrigine (50 mg/kg i.p.). Formalin-induced increases in glutamate levels in SCDH were lowered significantly, as compared with the controls, with all drugs both in the first phase and second phases, with the greatest effects for riluzole and gabapentin. Similar suppressive effects of the drugs were observed on formalin-induced increases in spinal aspartate, except that gabapentin and lamotrigine produced effects only during the second phase. Riluzole produced profound and prolonged reductions in the spinal levels of glutamate and aspartate both for basal and formalin-stimulated release. In conclusion, the results suggest that the anti-convulsant agents gabapentin, lamotrigine and riluzole may reduce the development of hyperalgesia in a rat model of neuropathic pain by reducing the spinal release of glutamate. Riluzole's pronounced suppressive effects on spinal EAA levels is attributed to its established role as a glutamate release inhibitor and an enhancer of glutamate transporter activity.

Acetyl-l-carnitine protects striatal neurons against in vitro ischemia: The role of endogenous acetylcholine

The neuronal death after ischemia is closely linked to the essential role of mitochondrial metabolism. Inhibition of mitochondrial respiratory chain reduces ATP generation leading to a dysregulation of ion metabolism. Acetyl-L-carnitine (ALC) influences the maintenance of key mitochondrial proteins for maximum energy production and it may play a neuroprotective role in some pathological conditions. In this study we have analyzed ALC-mediated neuroprotection on an in vitro model of brain ischemia. Field potential recordings were obtained from a rat corticostriatal slice preparation. In vitro ischemia (oxygen and glucose deprivation) was delivered by switching to a solution in which glucose was omitted and oxygen was replaced with N2. Ten minutes of in vitro ischemia caused an irreversible loss of the field potential amplitude. Pretreatment with ALC produced a progressive and dose-dependent recovery of the field potential amplitude following in vitro ischemia. The neuroprotective effect of ALC was stereospecific since the pretreatment with two different carnitine-related compounds did not cause neuroprotection. The choline transporter inhibitor hemicholinium-3 blocked the neuroprotective effect of ALC. ALC-mediated neuroprotection was also prevented either by the non-selective muscarinic antagonist scopolamine, or by the putative M2-like receptor antagonist methoctramine. Conversely, the effect of ALC was not altered by the M1-like receptor antagonist pirenzepine. These findings show that ALC exert a neuroprotective action against in vitro ischemia. This neuroprotective effect requires the activity of choline uptake system and the activation of M2 muscarinic receptors.

Functional Pharmacology in Human Brain

Most neurological and psychiatric disorders involve selective or preferential impairments of neurotransmitter systems. Therefore, studies of functional transmitter pathophysiology in human brain are of unique importance in view of the development of effective, mechanism-based, therapeutic modalities. It is well known that central nervous system functional proteins, including receptors, transporters, ion channels, and enzymes, can exhibit high heterogeneity in terms of structure, function, and pharmacological profile. If the existence of types and subtypes of functional proteins amplifies the possibility of developing selective drugs, such heterogeneity certainly increases the likelihood of interspecies differences. It is therefore essential, before choosing animal models to be used in preclinical pharmacology experimentation, to establish whether functionally corresponding proteins in men and animals also display identical pharmacological profiles. Because of evidence that scaffolding proteins, trafficking between plasma membrane and intracellular pools, phosphorylation and allosteric modulators can affect the function of receptors and transporters, experiments with human clones expressed in host cells where the environment of native receptors is rarely reproduced should be interpreted with caution. Thus, the use of neurosurgically removed fresh human brain tissue samples in which receptors, transporters, ion channels, and enzymes essentially retain their natural environment represents a unique experimental approach to enlarge our understanding of human brain processes and to help in the choice of appropriate animal models. Using this experimental approach, many human brain functional proteins, in particular transmitter receptors, have been characterized in terms of localization, function, and pharmacological properties.

NMDA-induced preconditioning attenuates synaptic plasticity in the rat hippocampus

It was recently demonstrated that glutamate could precondition hippocampal slices against the damaging effects of hypoxia, and we have now extended this observation by investigating (i) the ability of glutamate receptor agonists to act as preconditioning agents and (ii) the effects of preconditioning on synaptic plasticity. Using rat hippocampal slices, 15 microM NMDA applied for 10 min (chemical insult) caused abolition of the population spike potentials (PS) followed by approximately 33% recovery at 60 min post-insult. In comparison, a 5 min preconditioning exposure of 10 microM NMDA given 30 min prior to the insult significantly improved the recovery to 69%. Preconditioning did not alter paired pulse facilitation; however, it significantly enhanced paired pulse depression and reduced population spike long-term potentiation (PS-LTP) and LTP in field recordings. This effect on PS-LTP appeared to be NMDA receptor dependent and was blocked by the nitric oxide synthase inhibitors nitro-L-arginine methyl ester (L-NAME) and 7-nitro indazole (7-NI) but not by the adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). We conclude that preconditioning by NMDA can improve recovery following acute insults but may have deleterious effects on neuronal plasticity.

Voltage-gated cation channel modulators for the treatment of stroke

Neuronal voltage-gated cation channels regulate the transmembrane flux of calcium, sodium and potassium. Neuronal ischaemia occurring during acute ischaemic stroke results in the breakdown in the normal function of these ion channels, contributing to a series of pathological events leading to cell death. A dramatic increase in the intracellular concentration of calcium during neuronal ischaemia plays a particularly important role in the neurotoxic cascade resulting in stroke-related acute neurodegeneration. One approach to provide therapeutic benefit following ischaemic stroke has been to target neuronal voltage-gated cation channels, and particularly blockers of calcium and sodium channels, for post-stroke neuroprotection. A recent development has been the identification of openers of large-conductance calcium- and voltage-dependent potassium channels (maxi-K channels), which hyperpolarize ischaemic neurons, reduce excitatory amino acid release, and reduce ischaemic calcium entry. Thus far, targeting these voltage-gated cation channels has not yet yielded significant clinical benefit. The reasons for this may involve the lack of small-molecule blockers of many neuronal members of these ion channel families and the design of preclinical stroke models, which do not adequately emulate the clinical condition and hence lack sufficient rigor to predict efficacy in human stroke. Furthermore, there may be a need for changes in clinical trial designs to optimise the selection of patients and the course of drug treatment to protect neurons during all periods of potential neuronal sensitivity to neuro-protectants. Clinical trials may also have to be powered to detect small effect sizes or be focused on patients more likely to respond to a particular therapy. The development of future solutions to these problems should result in an improved probability of success for the treatment of stroke.

Understanding regulation of nerve cell death by mGluRs as a method for development of successful neuroprotective strategies

A common cause of nerve cell death often leading to vascular dementia is ischemic stroke. Attempts to develop clinically effective stroke treatment and prevention strategies based on pharmacological manipulations of a single mechanism have not led to clinical success. Analysis of clinical neuroprotection trials suggests that combination treatments may be more effective. To identify optimal components for such treatment, N-methyl-d-aspartate receptor (NMDAR) activation-induced cell death in organotypic hippocampal preparations was studied as a model of neurodegeneration that occurs in association with stroke or vascular dementia. Pharmacological manipulation of metabotropic glutamate receptors mGluR1 and 5 resulted in significant reduction of nerve cell susceptibility to NMDA-induced injury, suggesting that these receptors may function as physiological regulators of neuronal vulnerability. cDNA microarray analysis of over 1000 brain-related genes performed after the neuroprotective activation of group I metabotropic glutamate receptors (mGluRs) revealed a complex pattern of activation and inactivation of seemingly unrelated genes responsible for regulation of neuronal excitability, inflammation, cell death pathways, cell adhesion and transcriptional activation. Combined pharmacological targeting of these processes may provide basis for clinical trials of effective neuroprotective compounds.

Glutamate efflux from human cerebrocortical slices during ischemia: vesicular-like mode of glutamate release and sensitivity to A2A adenosine receptor blockade

Glutamate extracellular accumulation is an early event in brain ischemia triggering excitotoxic neuron damage. We have investigated how to control the glutamate efflux from human cerebrocortical slices superfused in conditions simulating an acute ischemic insult (oxygen and glucose deprivation). The efflux of previously accumulated [3H]D-aspartate or endogenous glutamate increased starting 18 min after exposure to ischemia and returned almost to basal values in 6 min reperfusion with standard medium. Superfusion with Ca2+-free, EGTA (0.5 mM)-containing medium or with medium containing tetrodotoxin (TTX; 0.5 microM) inhibited the ischemia (24 min)-evoked [3H]D-aspartate efflux by about 50% and 65%, respectively. The ischemia (24 or 36 min)-evoked efflux of [3H]D-aspartate or endogenous glutamate was reduced at least 40% by the adenosine A(2A) receptor antagonist SCH 58261 (1 microM); the compound was effective when added up to 15 min after exposure to ischemia. No effect of SCH 58261 on the ischemia-evoked [3H]D-aspartate was found in Ca2+-free, EGTA-containing medium. To conclude, a significant component of the ischemia-evoked glutamate efflux in human cerebrocortical slices seems to occur by a vesicular-like mechanism. Endogenously released adenosine is likely to activate A(2A) receptors that enhance vesicular-like glutamate release during ischemia; A(2A) receptor antagonists would deserve consideration for their neuroprotective potential.

Effect of lamotrigine treatment on epileptogenesis: an experimental study in rat

Prevention of epileptogenesis in patients with acute brain damaging insults like status epilepticus (SE) is a major challenge. We investigated whether lamotrigine (LTG) treatment started during SE is antiepileptogenic or disease-modifying. To mimic a clinical study design, LTG treatment (20 mg/kg) was started 2 h after the beginning of electrically induced SE in 14 rats and continued for 11 weeks (20 mg/kg per day for 2 weeks followed by 10 mg/kg per day for 9 weeks). One group of rats (n = 14) was treated with vehicle. Nine non-stimulated rats with vehicle treatment served as controls. Outcome measures were occurrence of epilepsy, severity of epilepsy, and histology (neuronal loss, mossy fiber sprouting). Clinical occurrence of seizures was assessed with 1-week continuous video-electroencephalography monitoring during the 11th (i.e. during treatment) and 14th week (i.e. after drug wash-out) after SE. LTG reduced the number of electrographic seizures during SE to 43% of that in the vehicle group (P < 0.05). In the vehicle group, 93% (13/14), and in the LTG group, 100% (14/14) of the animals, developed epilepsy. In both groups, 64% of the rats had severe epilepsy (seizure frequency >1 per day). The mean frequency of spontaneous seizures, seizure duration, or behavioral severity of seizures did not differ between groups. The severity of hippocampal neuronal damage and density of mossy fiber sprouting were similar. In LTG-treated rats with severe epilepsy, however, the duration of seizures was shorter (34 versus 54s, P < 0.05) and the behavioral seizure score was milder (1.4 versus 3.4, P < 0.05) during LTG treatment than after drug wash-out. LTG treatment started during SE and continued for 11 weeks was not antiepileptogenic but did not worsen the outcome. These data, together with earlier studies of other antiepileptic drugs, suggest that strategies other than Na(+)-channel blockade should be explored to modulate the molecular cascades leading to epileptogenesis after SE.

The effects of citicoline and lamotrigine alone and in combination following permanent middle cerebral artery occlusion in rats

The neuroprotective efficacies of citicoline and lamotrigine, alone and in combination, were investigated in experimental permanent focal ischemia. Seven groups of adult male rats underwent focal cerebral ischemia and were given the following treatments: placebo (P), low and high doses of citicoline (C250 and C500, 250 and 500 mg/kg/day i.p., respectively), low and high doses of lamotrigine (L50 and L100, 50 and 100 mg/kg/day p.o., respectively), and combination regimes of both drugs in low (C250 + L50) and high doses (C500 + L100). Citicoline, but not lamotrigine, exerted neuroprotective efficacy during this acute ischemic stroke model. The citicoline and lamotrigine combination did not provide a significant additive neuroprotective effect.

Levetiracetam protects against kainic acid-induced toxicity

We investigated the Levetiracetam (LVT) ability to protect the brain against kainic acid (KA) induced neurotoxicity. Brain injury was induced by intraperitoneal administration of KA (10 mg/kg). Sham brain injury rats were used as controls. Animals were randomized to receive either LVT (50 mg/kg) or its vehicle (1 ml/kg) 30 min. before KA administration. Animals were sacrificed 6 hours after KA injection to measure brain malonildialdehyde (MDA), glutathione levels (GSH) and the mRNA for interleukin-1beta (IL-1beta) in the cortex and in the diencephalon. Behavioral changes were also monitored. Intraperitoneal administration of LVT decreased significantly MDA in the cortex (KA + vehicle = 0.25 +/- 0.03 nmol/mg protein; KA + LVT = 0.13 +/- 0.01 nmol/mg protein; P < 0.005), and in the diencephalons (KA + vehicle = 1,01 +/- 0.2 nmol/mg protein; KA + LVT = 0,33 +/- 0,08 nmol/mg protein; P < 0.005), prevented the brain loss of GSH in both cortex (KA + vehicle = 5 +/- 1 micromol/g protein; KA + LVT = 15 +/- 2 micromol/g protein; P < 0.005) and diencephalons (KA + vehicle = 9 +/- 0.8 micromol/g protein; KA + LVT = 13 +/- 0.3 micromol/g protein; P < 0.05), reduced brain IL-1beta mRNA and markedly controlled seizures. Histological analysis showed a reduction of cell damage in LVT treated samples. The present data indicate that LVT displays neuro-protective effects against KA induced brain toxicity and suggest that these effects are mediated, at least in part, by inhibition of lipid peroxidation.

Lamotrigine treatment for post-stroke pathological laughing and crying

Pathologic laughing and crying (PLC) is a common distressing and socially disabling condition in stroke patients. Antidepressants, particularly selective serotonin reuptake inhibitors (SSRIs), have been increasingly recognized as the treatment of choice for pathologic crying (PC). However, little is known about etiologies and other treatment options for various clinical manifestations of PLC. This case report illustrates the beneficial effect of lamotrigine, a novel antiepileptic drug with antidepressant and mood-stabilizing properties in post-stroke PLC. A 60-year-old woman developed PLC after an ischemic stroke affecting the left frontal and temporal lobes. She was treated with lamotrigine initially at the dose of 50 mg a day, which was gradually increased to 100 mg a day over a 4-week period. There was a significant and rapid recovery in both laughing and crying components of PCL with lamotrigine treatment. The symptoms of pathologic laughing have shown a better response to lamotrigine than PC. Controlled investigations are needed to evaluate the beneficial as well as the differential effects of lamotrigine on PLC.

Synaptic plasticity in the ischaemic brain

Activity-dependent long-term potentiation (LTP) of excitatory neurotransmission underlies specific forms of associative learning and memory. A brief period of energy deprivation induces LTP in specific subsets of neurons; this synaptic plasticity might contribute to the delayed effects of brain ischaemia. In this review, we discuss the similarities and differences between LTP induced by energy deprivation and "physiological" LTP. On the basis of recent studies, we propose that pathological plasticity induced by energy deprivation can play a part in delayed neuronal death in the hippocampus and the striatum after global ischaemia and in the conversion of ischaemic penumbra to infarct core after focal ischaemia. We discuss evidence that ischaemia could also induce protective and reparative forms of neuronal plasticity that may play a part in ischaemic tolerance and poststroke recovery.

Lamotrigine and remacemide protect striatal neurons against in vitro ischemia: an electrophysiological study

In the present study, we investigated the cellular and synaptic mechanisms underlying the neuroprotective action of lamotrigine and remacemide. Both drugs, in fact, have been reported to exert a neuroprotective action in in vivo animal models of ischemia. To address this issue, electrophysiological recordings and cell swelling measurements were performed from striatal neurons in control condition and during combined oxygen and glucose deprivation (in vitro ischemia) in a brain slice preparation. Lamotrigine, remacemide, and the active desglycinyl metabolite of remacemide, D-REMA, induced a concentration-dependent reduction of both repetitive firing discharge and excitatory postsynaptic potentials. However, while remacemide and D-REMA exerted their inhibitory action on glutamatergic transmission by blocking NMDA receptors, lamotrigine exerted a preferential presynaptic action, as indicated by its ability to increase paired-pulse facilitation. Both remacemide and lamotrigine were found to be neuroprotective against the irreversible field potential loss and cell swelling induced by in vitro ischemia, and coadministration of low concentrations of these drugs exerted an additive neuroprotective action. A combined use of lamotrigine and remacemide could be employed in clinical trials to enhance neuroprotection in neurological disorders involving an abnormal striatal glutamatergic transmission.

Antiepileptic drugs as a possible neuroprotective strategy in brain ischemia

Several new antiepileptic drugs (AEDs) have been introduced for clinical use recently. These new AEDs, as did the classic AEDs, target multiple cellular sites both pre- and postsynaptically. The major common goal of the pharmacological treatment using AEDs is to counteract abnormal brain excitability by either decreasing excitatory transmission or enhancing neuronal inhibition. Interestingly, an excessive release of excitatory amino acids and a reduced neuronal inhibition also occur in brain ischemia. Thus, recently, the use of AEDs as a possible neuroprotective strategy in brain ischemia is receiving increasing attention, and many AEDs have been tested in animal models of stroke, providing encouraging results. Experimental studies utilizing global or focal ischemia in rodents have provided insights into the possible neuroprotective action of the various AEDs. However, the implication of these studies in the treatment of acute stroke in humans is not always direct. In fact, various clinical studies with drugs targeting the same voltage- and ligand-gated channels modulated by most of the AEDs failed to show neuroprotection. The differential mechanisms that underlie the development of focal ischemic injury in experimental animal models versus human stroke require further investigation to open a new therapeutic perspective for neuroprotection that might be applicable in the future.

Transient and progressive electrophysiological alterations in the corticostriatal pathway in a mouse model of Huntington's disease

Alterations in the corticostriatal pathway may precede symptomatology and striatal cell death in Huntington's disease (HD) patients. Here we examined spontaneous EPSCs in striatal medium-sized spiny neurons in slices from a mouse model of HD (R6/2). Spontaneous EPSC frequency was similar in young (3-4 weeks) transgenics and controls but decreased significantly in transgenics when overt behavioral symptoms began (5-7 weeks) and was most pronounced in severely impaired transgenics (11-15 weeks). These differences were maintained after bicuculline or tetrodotoxin, indicating they were specific to glutamatergic input and likely presynaptic in origin. Decreases in presynaptic and postsynaptic protein markers, synaptophysin and postsynaptic density-95, occurred in 11-15 week R6/2 mice, supporting the electrophysiological results. Furthermore, isolated, large-amplitude synaptic events (>100 pA) occurred more frequently in transgenic animals, particularly at 5-7 weeks, suggesting additional dysregulation of cortical inputs. Large events were blocked by tetrodotoxin, indicating a possible cortical origin. Addition of bicuculline and 4-aminopyridine facilitated the occurrence of large events. Riluzole, a compound that decreases glutamate release, reduced these events. Together, these observations indicate that both progressive and transient alterations occur along the corticostriatal pathway in experimental HD. These alterations are likely to contribute to the selective vulnerability of striatal medium-sized spiny neurons.

Ionotropic glutamate receptors: still a target for neuroprotection in brain ischemia? Insights from in vitro studies

Although experimental studies have widely shown that the pharmacological blockade of ionotropic glutamate receptors reduces ischemic damage, clinical trials with classical AMPA and NMDA glutamate receptor antagonists have provided negative results. To address the involvement of ionotropic glutamate receptors in ischemic damage, corticostriatal brain slices were prepared from adult rats. Extracellular recordings were performed in the striatum after stimulation of the glutamatergic corticostriatal fibres. In vitro ischemia was induced for a 10-min period by omitting oxygen and glucose from the external medium. Under control conditions, ischemia produced an irreversible loss of the corticostriatal field potential amplitude, AP5, a competitive NMDA receptor antagonist, induced a slight rescue of the potential, while ifenprodil, a positive modulator of the proton sensor of the NMDA receptors, allowed a complete recovery from the ischemic insult. Similar neuroprotection was achieved by utilizing either CNQX, a broad spectrum AMPA receptors antagonist, or Joro spider toxin, a selective blocker of calcium permeable AMPA receptors. Interestingly, while CNZX also fully suppressed physiological excitatory transmission, Joro spider toxin was ineffective on this parameter. Finally, lamotrigine and remacemide, two antiepileptic drugs that differentially affect excitatory transmission, exerted neuroprotective effects against ischemia. Noticeably, a combination of low concentrations of these two drugs exerted a stronger neuroprotection than a single drug given in isolation. Thus, it might be possible to reach a neuroprotective action by utilizing doses of these compounds low enough to avoid side effects. Our experimental data still support the idea that a negative modulation of excitatory transmission can be neuroprotective against ischemia. In addition, our findings support the concept that it is possible to produce a significant neuroprotective action in the absence of a relevant interference with normal synaptic transmission.

Inhibition of rho-kinase-induced myristoylated alanine-rich C kinase substrate (MARCKS) phosphorylation in human neuronal cells by H-1152, a novel and specific Rho-kinase inhibitor

The functions of small G protein Rho-associated kinase (Rho-kinase) have been determined in muscle and non-muscle cells, but, particularly in neuronal cells, its effector(s) has not been well known. Recently, we preliminarily reported that Rho-kinase phosphorylates the Ser159 residue in myristoylated alanine-rich C kinase substrate (MARCKS) in vitro, but it remains obscure in vivo. To further clarify this point, we developed an isoquinolinesulfonamide derivative, H-1152, that is a more specific, stronger and membrane-permeable inhibitor of Rho-kinase with a Ki value of 1.6 nM, but poor inhibitor of other serine/threonine kinases. H-1152 dose-dependently inhibited the phosphorylation of MARCKS in human neuroteratoma (NT-2) cells stimulated by Rho-activator lysophosphatidic acid (LPA), which was determined by phosphorylation site-specific antibody against phospho-Ser159 in MARCKS, whereas it hardly inhibited the phosphorylation stimulated by phorbol-12,13-dibutyrate (PDBu). In contrast, two other Rho-kinase inhibitors, HA-1077 at 30 microM and Y-27632 at 10-30 microM, inhibited the phosphorylation of MARCKS in the cells stimulated by LPA and PDBu. A PKC inhibitor Ro-31-8220 selectively inhibited PDBu-induced phosphorylation of MARCKS. Taken together with our previous results, the present findings strongly suggest that Rho/Rho-kinase phosphorylates MARCKS at Ser159 residue in neuronal cells in response to LPA stimulation and that H-1152 is a useful tool to confirm Rho-kinase function(s) in cells and tissues.

Blockade of striatal adenosine A2A receptor reduces, through a presynaptic mechanism, quinolinic acid-induced excitotoxicity: possible relevance to neuroprotective interventions in neurodegenerative diseases of the striatum

The aim of the present study was to evaluate whether, and by means of which mechanisms, the adenosine A2A receptor antagonist SCH 58261 [5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine] exerted neuroprotective effects in a rat model of Huntington's disease. In a first set of experiments, SCH 58261 (0.01 and 1 mg/kg) was administered intraperitoneally to Wistar rats 20 min before the bilateral striatal injection of quinolinic acid (QA) (300 nmol/1 microl). SCH 58261 (0.01 but not 1 mg/kg, i.p.) did reduce significantly the effects of QA on motor activity, electroencephalographic changes, and striatal gliosis. Because QA acts by both increasing glutamate outflow and directly stimulating NMDA receptors, a second set of experiments was performed to evaluate whether SCH 58261 acted by preventing the presynaptic and/or the postsynaptic effects of QA. In microdialysis experiments in naive rats, striatal perfusion with QA (5 mm) enhanced glutamate levels by approximately 500%. Such an effect of QA was completely antagonized by pretreatment with SCH 58261 (0.01 but not 1 mg/kg, i.p.). In primary striatal cultures, bath application of QA (900 microm) significantly increased intracellular calcium levels, an effect prevented by the NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate]. In this model, bath application of SCH 58261 (15-200 nm) tended to potentiate QA-induced calcium increase. We conclude the following: (1) the adenosine A2A receptor antagonist SCH 58261 has neuroprotective effects, although only at low doses, in an excitotoxic rat model of HD, and (2) the inhibition of QA-evoked glutamate outflow seems to be the major mechanism underlying the neuroprotective effects of SCH 58261.

12-hydroxyeicosatetrenoate (12-HETE) attenuates AMPA receptor-mediated neurotoxicity: evidence for a G-protein-coupled HETE receptor

12-hydroxyeicosatetraenoic acid (12-HETE) is a neuromodulator that is synthesized during ischemia. Its neuronal effects include attenuation of calcium influx and glutamate release as well as inhibition of AMPA receptor (AMPA-R) activation. Because 12-HETE reduces ischemic injury in the heart, we examined whether it can also reduce neuronal excitotoxicity. When treated with 12-(S)HETE, cortical neuron cultures subjected to AMPA-R-mediated glutamate toxicity suffered up to 40% less damage than untreated cultures. The protective effect of 12-(S)HETE was concentration-dependent (EC50 = 88 nm) and stereostructurally selective. Maximal protection was conferred by 300 nm 12-(S)HETE; 300 nm 15-(S)HETE was similarly protective, but 300 nm 5-(S)HETE was less effective. The chiral isomer 12-(R)HETE offered no protection; neither did arachidonic acid or 12-(S)hydroperoxyeicosatetraenoic acid. Excitotoxicity was calcium-dependent, and 12-(S)HETE was demonstrated to protect by inactivating N and L (but not P) calcium channels via a pertussis toxin-sensitive mechanism. Calcium imaging demonstrated that 12-(S)HETE also attenuates glutamate-induced calcium influx into neurons via a pertussis toxin-sensitive mechanism, suggesting that it acts via a G-protein-coupled receptor. In addition, 12-(S)HETE stimulates GTPgammaS binding (indicating G-protein activation) and inhibits adenylate cyclase in forskolin-stimulated cultures over the same concentration range as it exerts its anti-excitotoxic and calcium-influx attenuating effects. These studies demonstrate that 12-(S)HETE can protect neurons from excitotoxicity by activating a G(i/o)-protein-coupled receptor, which limits calcium influx through voltage-gated channels.

Nitric oxide-dependent damage to neuronal mitochondria involves the NMDA receptor

Cytokine-stimulated astrocytes produce nitric oxide, which can inhibit components of the mitochondrial respiratory chain. We have previously demonstrated that prolonged exposure (48 h) to rat astrocytic nitric oxide damages complexes II--III and IV of neighbouring rat neurons in coculture, resulting in neuronal death. Expanding on these observations, we have now shown that the NMDA receptor antagonist, MK-801, prevents this damage, suggesting involvement of glutamate. We postulate that astrocyte-derived nitric oxide stimulates release of neuronal glutamate. Indeed we demonstrate that neurons incubated with nitric oxide-generating astrocytes display enhanced glutamate release. Furthermore, direct exposure to the nitric oxide donor, DETA-NONOate resulted in a loss of activity of all the neuronal mitochondrial complexes, which was again prevented by MK-801. Thus, nitric oxide, generated by both cytokine-stimulated astrocytes and by a nitric oxide donor, causes activation of the NMDA receptor leading to damage to the neuronal mitochondrial respiratory chain. Glutamate exposure is known to damage the neuronal mitochondrial respiratory chain via neuronal nitric oxide synthase. Therefore, we propose that astrocyte-derived nitric oxide is capable of eliciting neuronal glutamate release, which in turn activates the neuronal NMDA receptor and stimulates further formation of reactive nitrogen species via neuronal nitric oxide synthases, leading to mitochondrial damage and neuronal death. Our findings support the hypothesis that glutamate, reactive nitrogen species and mitochondrial dysfunction may have a role in the neurodegenerative process.

The novel and specific Rho-kinase inhibitor (S)-(+)-2-methyl-1-[(4-methyl-5-isoquinoline)sulfonyl]-homopiperazine as a probing molecule for Rho-kinase-involved pathway

We have developed several kinds of protein kinase inhibitors, which are classified as isoquinolinesulfonamides and characterized as ATP competitive inhibitors of Ser/Thr protein kinases. These include H9, H89, KN62, and 1-(5-isoquinolinesulfonyl)-homopiperazine (HA-1077) against protein kinase C (PKC), protein kinase A, Ca(2+)/calmodulin-dependent protein kinase II, and Rho-kinase, respectively, and they have been used widely to confirm the involvement of the target protein kinase in biological or physiological reaction(s). In some cases, inhibitors have predicted the involvement of the target protein kinase in cell or tissue before its precise mechanism or its effector was defined. On a clinical level, we developed the Rho-kinase inhibitor HA-1077 as an anti-spastic that effectively suppresses the spasm of cerebral arteries after subarachnoid hemorrhage. We have improved HA-1077 to obtain (S)-(+)-2-methyl-1-[(4-methyl-5-isoquinoline)sulfonyl]-homopiperazine (H-1152P), which is a more selective inhibitor of Rho-kinase, with a K(i) value of 1.6 nM for Rho-kinase, 630 nM for protein kinase A, and 9270 nM for PKC. This inhibitor suppressed the phosphorylation of myristoylated alanine-rich C-kinase substance (MARCKS) in neuronal cells stimulated with lysophosphatidic acid, whose phosphorylation site was confirmed to be the Ser159 residue, using a phosphorylation site-specific antibody. In contrast, phorbol 12-myristate 13-acetate-induced phosphorylation of MARCKS was scarcely inhibited by H-1152P. Furthermore, lysophosphatidic acid-stimulated phosphorylation in neuronal cells was characterized as a C3 toxin-sensitive event. Our results show that the Rho-kinase inhibitor targets a protein with a well-known function, MARCKS in neuronal cells. Although MARCKS is widely recognized as a substrate of PKC, our results raise the possibility that MARCKS is a target protein of Rho-kinase in neuronal cells. In this review, we address the possible role of Rho-kinase in neuronal functions, using the Rho-kinase specific inhibitor H-1152P.

Neuroprotective actions in vivo and electrophysiological actions in vitro of 202W92

202W92 (R-(-)-2,4-diamino-6-(fluromethyl)-5-(2,3,5-trichlorophenyl)pyrimidine) is a novel compound in the same chemical series as the antiepileptic drug lamotrigine and the neuroprotective sipatrigine. Here 202W92 was quantitatively assessed as a neuroprotective agent in focal cerebral ischaemia, and as an inhibitor of sodium and calcium channels and of synaptic transmission. In the rat permanent middle cerebral artery occlusion (MCAO) model of acute focal ischaemia, 202W92 reduced infarct volume by 75% in cortex and by 80% in basal ganglia, with ED(50) approximately 2 mg/kg (single i.v. dose, 10 min post-occlusion). In whole-cell current recordings from single cells, 202W92 completely and reversibly inhibited voltage gated sodium channels (IC(50) 3 x 10(-6) M) in rat freshly-isolated cortical neurons and in the GH(3) pituitary cell line. 202W92 also inhibited a nifedipine-sensitive fraction (approximately 35%) of native high-voltage-activated (HVA) calcium current in rat cortical neurons (IC(50) 15 x 10(-6) M) and weakly inhibited low-voltage-activated (LVA) calcium currents of the recombinant alpha1I-mediated T-type (IC(50)>100 x 10(-6) M). The drug inhibited the amplitude and frequency of 4-aminopyridine-evoked glutamatergic excitatory post-synaptic currents (EPSCs). In conclusion, 202W92 is an effective neuroprotective agent when administered post-ischaemia and a potent sodium channel inhibitor in vitro.