Nefiracetam enhances acetylcholine outflow from the frontal cortex: in vivo microdialysis study in the rat

Anticonvulsant and neuroprotective effects of the novel nootropic agent nefiracetam on kainic acid-induced seizures in rats

Nefiracetam is a novel pyrrolidone-type nootropic agent, and it has been reported to possess a potential for antiepileptic therapy as well as cognition-enhancing effects. We investigated the anticonvulsant and neuroprotective effects of nefiracetam in kainic acid-induced seizures of rats, compared with levetiracetam and standard antiepileptic drugs. Subcutaneous injection of kainic acid (10 mg/kg) induced typical behavioral seizures such as wet dog shakes and limbic seizures and histopathological changes in the hippocampus (degeneration and loss of pyramidal cells in CA1 to CA4 areas). Nefiracetam (25, 50 and 100 mg/kg po) had no effect on the behavioral seizures and dose-dependently inhibited the hippocampal damage. In contrast, levetiracetam, a pyrrolidone-type antiepileptic drug, inhibited neither. Valproic acid and ethosuximide prevented the hippocampal damage without attenuating the behavioral seizures as nefiracetam. Zonisamide and phenytoin did not inhibit the behavioral seizures, while zonisamide enhanced the hippocampal damage and phenytoin increased the lethality rate. Carbamazepine inhibited the behavioral seizures at 50 mg/kg and enhanced that at 100 mg/kg, and it completely inhibited the hippocampal damage at both doses. We have previously reported that anticonvulsant spectrum of nefiracetam paralleled that of zonisamide, phenytoin or carbamazepine in standard screening models. However, the pharmacological profile of nefiracetam was closer to valproic acid or ethosuximide than that of zonisamide, phenytoin or carbamazepine in this study. These results suggest that anticonvulsant spectrum and mechanism of nefiracetam are distinct from those of standard antiepileptic drugs, and nefiracetam possesses a neuroprotective effect that is unrelated to seizure inhibition.

Effects of Nefiracetam, a novel pyrrolidone-type nootropic agent, on the amygdala-kindled seizures in rats

PURPOSE

Nefiracetam (NEF) is a novel pyrrolidonetype nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the effects of NEF in amygdala-kindled seizures and its potential for antiepileptic therapy.

METHODS

Effects of NEF on fully amygdala-kindled seizures and development of amygdala-kindled seizures were investigated in rats and compared with those of levetiracetam (LEV), a pyrrolidone-type antiepileptic drug (AED).

RESULTS

In fully amygdala-kindled rats, NEF (25, 50, and 100 mg/kg, p.o.) decreased afterdischarge induction, afterdischarge duration, seizure stage, and motor seizure duration in a dose-dependent manner. LEV (25, 50, and 100 mg/kg, p.o.) had no effects on afterdischarge induction and slightly decreased afterdischarge duration, whereas it markedly decreased seizure stage and motor seizure duration. In contrast to the results in fully amygdala-kindled rats, NEF (25 and 50 mg/kg/day, p.o.) had few or no effects on the development of amygdala-kindled seizures. As well as fully amygdala-kindled seizures, LEV (50 mg/kg/day, p.o.) markedly inhibited the development of behavioral seizures without reducing daily afterdischarge duration.

CONCLUSIONS

Although NEF possesses potent anticonvulsant effects on fully amygdala-kindled seizures, it has few or no effects on the development of amygdala-kindled seizures. LEV shows marked anticonvulsant effects on both phases of kindling. In fully amygdala-kindled rats, NEF inhibits both electroencephalographic and behavioral seizures, whereas LEV inhibits only behavioral seizures. This double dissociation suggests that NEF has a distinct anticonvulsant spectrum and mechanisms from those of LEV.

Anticonvulsant properties of the novel nootropic agent nefiracetam in seizure models of mice and rats

PURPOSE

Nefiracetam (NEF) is a novel pyrrolidone-type nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the anticonvulsant effect of NEF and its potential for antiepileptic therapy.

METHODS

The anticonvulsant properties of NEF were investigated in experimental seizure models of mice and rats, compared with levetiracetam (LEV) and other standard antiepileptic drugs [AEDs; zonisamide (ZNS), phenytoin (PHT), carbamazepine (CBZ), valproic acid (VPA), diazepam (DZP), and ethosuximide (ESM)]. With reference to standard programs for evaluating potential AEDs, the study included the traditional maximal electroshock seizure and subcutaneous chemoconvulsant (pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate) seizure tests and two threshold models (the increasing-current electroshock seizure test and intravenous pentylenetetrazole seizure threshold test). Neurotoxic activities were examined with the rotarod test and traction test.

RESULTS

NEF inhibited electroshock-induced seizures at nontoxic doses, whereas it had no effect on seizures chemically induced by pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate. The anticonvulsant spectrum of NEF paralleled that of ZNS, PHT, and CBZ. The anticonvulsant efficacy of NEF was comparable with that of ZNS and less potent than that of PHT, CBZ, and DZP. However, the safety margin of NEF was superior to that of ZNS, CBZ, VPA, and DZP. LEV showed only slight anticonvulsant effects in threshold models, and it was not effective in conventional screening models.

CONCLUSIONS

These results suggest that NEF has distinct anticonvulsant spectrum and mechanisms from those of LEV. NEF is an orally active and safe AED, and it possesses a potential for antiepileptic therapy.

Ion channel modulators that enhance acetylcholine release: potential therapies for Alzheimer’s disease

Enhancing the release of acetylcholine (ACh) in the brain is one approach to increasing neuronal activity, restoring central cholinergic tone and improving attention and cognition. ACh release is modulated by both ligand-gated (gamma-amino butyric acid A receptors/benzodiazepine [GABA(A)/BDZ], nicotinic-acetylcholine and serotonin, 5-HT3) and voltage-gated (calcium and potassium) ion channels. Of the ligand-gated channel modulators, the BDZ receptor (BDZR) inverse agonists (beta-CCM, ZK 93426) enhance activity-dependent release in animals, whereas S-8510, a partial inverse agonist, and the BDZR antagonist, flumazenil, show enhancement regardless of the behavioural state of the animal. Some of these agents have undergone limited clinical evaluation for Alzheimer's disease (AD) (ZK 93426, flumazenil, S-8510), but their potential anxiogenic liability makes their therapeutic use uncertain until more clinical data are available. Within the group of nicotinic agonists, ABT-418, though less potent than nicotine and epibatidine in promoting ACh release in vitro, was clinically evaluated based on its in vivo profile. Its lack of oral bioavailability has limited its acceptability, though transdermal administration has been used to circumvent this deficiency. Serotonin 5-HT3 receptor modulators have not been advanced for clinical evaluation for the treatment of AD. Among the voltage-gated ion channel modulators affecting L- or N-type calcium channels, nefiracetam, a nootropic agent, also increased ACh release in animal studies. It is currently undergoing clinical evaluation for AD, though a need for more potent and brain selective calcium channel blockers exists. Potassium channel modulators have been the most studied ACh release enhancing agents and several of these compounds (4-AP, 3,4-DAP, linopirdine) have been clinically evaluated. In AD patients, 4-AP, an A-type K+ channel blocker, elicited inconsistent and unremarkable effects. Linopirdine, whose enhancement of ACh release correlates with its ability to block M-type K+ channels, also produced disappointing clinical results, which may have been related to its suboptimal pharmacokinetic profile. Further work in this series has provided a compound (DMP 543) that should be a more reliable indicator of whether a blocker of this ion channel can activate the cholinergic system in man. This agent is currently undergoing clinical evaluation for AD.

Treatment of progressive supranuclear palsy and corticobasal degeneration

Success in treating patients with progressive supranuclear palsy and corticobasal degeneration remains exceedingly low. This finding probably relates to the widespread distribution of the pathological changes that account for the varied and complex spectrum of clinical manifestations. Dopaminergic drugs are regularly used for the parkinsonian features; however, these rarely result in more than modest benefit, and when better or sustained responses are obtained, as sometimes occurs in progressive supranuclear palsy, the clinical features are atypical and diagnosis is often delayed or not made in life. A variety of other treatments have been used in both disorders, sometimes directed at other specific features such as dystonia or myoclonus, and these treatments will be reviewed. Greater success in treating these disorders will require advances in our understanding of their cause(s) or the pathogenetic mechanisms underlying the neurodegenerative processes. The similarities in the molecular pathology of these four-repeat tauopathies suggests that important advances in the management of one will have a definite impact on the treatment of the other.

Effects of nefiracetam on the levels of brain-derived neurotrophic factor and synapsin I mRNA and protein in the hippocampus of microsphere-embolized rats

Our recent study demonstrated that nefiracetam, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, prevented impairment of the cyclic AMP (cAMP)/cAMP-responsive element binding (CREB) protein signaling pathway in sustained cerebral ischemia. The purpose of the present study was to determine whether nefiracetam has an effect on the expression of brain-derived neurotrophic factor (BDNF) and synapsin I mRNAs that are believed to be produced via CREB, and the alteration in their protein contents in the hippocampus after cerebral ischemia. Sustained cerebral ischemia was induced by injection of 700 microspheres into the right hemisphere of each rat. The rats were treated once daily with 10 mg/kg nefiracetam, p.o., from 15 h after the operation. Treatment with nefiracetam reduced the prolongation of the escape latency in the water maze test on days 7-9 after microsphere embolism-induced sustained cerebral ischemia, suggesting an improvement in the spatial learning function. Microsphere-embolized rats on day 5 showed decreases in BDNF and synapsin I mRNA levels and their protein contents in the ipsilateral hippocampus. Treatment with nefiracetam partially attenuated the decreases. These results suggest that enhancement of BDNF and synapsin I expression by nefiracetam treatment may be, at least in part, due to the improvement in the CREB binding activity, contributing to the prevention of learning and memory dysfunction after sustained cerebral ischemia.

Nefiracetam metabolism by human liver microsomes: role of cytochrome P450 3A4 and cytochrome P450 1A2 in 5-hydroxynefiracetam formation

An in-vitro study was conducted to investigate the metabolism of nefiracetam in human liver microsomes and to identify the enzymes responsible for the metabolism. Nefiracetam was hydroxylated by human liver microsomes to 5-hydroxynefiracetam (5-OHN). Eadie-Hofstee plots for the formation of 5-OHN suggested substrate activation. The kinetic parameters, apparent Km, Vmax, and Hill coefficient, for the formation of 5-OHN by pooled human liver microsomes were 4012 microM, 2.66 nmol min(-1) (mg protein)(-1), and 1.65, respectively. The formation of 5-OHN was significantly correlated with cytochrome P450 (CYP)3A4-mediated testosterone 6beta-hydroxylase activity and dextromethorphan N-demethylase activity. The 5-OHN formation was inhibited (94%) by antibody to human CYP3A4/5. The 5-OHN formation was also inhibited by the CYP3A4 inhibitors ketoconazole and troleandomycin, but not significantly inhibited by several other P450 inhibitors. The microsomes containing cDNA-expressed CYP3A4 formed 5-OHN with sigmoidal kinetics. CYP3A5-containing microsomes did not form 5-OHN. These results indicated that CYP3A, most likely CYP3A4, was the major isozyme responsible for the formation of 5-OHN in human liver microsomes. CYP1A2 and CYP2C19 microsomes were also capable of forming 5-OHN. However, the contribution of CYP1A2 was considered to be relatively minor compared with that of CYP3A4, and the contribution of CYP2C19 was assumed to be negligible, based on the result of the immunoinhibition study and taking into account both the turnover rate by each isozyme and the relative abundance of each isozyme in human liver. We conclude that on average the formation of 5-OHN, the major metabolite of nefiracetam, is principally mediated by CYP3A4 with a relatively minor contribution by CYP1A2.

Improvement by nefiracetam of beta-amyloid-(1-42)-induced learning and memory impairments in rats

1. We have previously demonstrated that continuous i.c.v. infusion of amyloid beta-peptide (A beta), the major constituent of senile plaques in the brains of patients with Alzheimer's disease, results in learning and memory deficits in rats. 2. In the present study, we investigated the effects of nefiracetam [N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, DM-9384] on A beta-(1-42)-induced learning and memory deficits in rats. 3. In the A beta-(1-42)-infused rats, spontaneous alternation behaviour in a Y-maze task, spatial reference and working memory in a water maze task, and retention of passive avoidance learning were significantly impaired as compared with A beta-(40-1)-infused control rats. 4. Nefiracetam, at a dose range of 1-10 mg kg(-1), improved learning and memory deficits in the A beta-(1-42)-infused rats when it was administered p.o. 1 h before the behavioural tests. 5. Nefiracetam at a dose of 3 mg kg(-1) p.o. increased the activity of choline acetyltransferase in the hippocampus of A beta-(1-42)-infused rats. 6. Nefiracetam increased dopamine turnover in the cerebral cortex and striatum of A beta-(1-42)-infused rats, but failed to affect the noradrenaline, serotonin and 5-hydroxyindoleacetic acid content. 7. These results suggest that nefiracetam may be useful for the treatment of patients with Alzheimer's disease.

Nefiracetam elevates extracellular acetylcholine level in the frontal cortex of rats with cerebral cholinergic dysfunctions: an in vivo microdialysis study

We determined the effect of nefiracetam, a novel cognitive enhancer, on the extracellular acetylcholine (ACh) level in the frontal cortex of freely moving rats, using a microdialysis technique without an acetylcholinesterase inhibitor in the perfusate. Treatment with nefiracetam (10 mg/kg, p.o.) produced a significant increase in the level of ACh in the brain dialysate, compared with the vehicle-treated group. This enhancing effect was also observed when the ACh level was elevated by administration of scopolamine (1 mg/kg, i.p.) at 45 min after the treatment with nefiracetam. In addition, perfusion of nefiracetam at the concentration of 10 microM significantly increased the extracellular ACh level in the frontal cortex of basal forebrain (BF)-lesioned rats, in which a marked decrease of the basal ACh level was observed in this region. These results suggest that enhancement of cortical ACh release by nefiracetam may contribute to an anti-amnesic effect on the learning deficits induced by treatment of scopolamine or BF-lesion in rats.

Effects of nefiracetam on amnesia animal models with neuronal dysfunctions

The effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide (nefiracetam; DM-9384), on learning and memory in several amnesia animal models with neuronal dysfunctions were investigated. Nefiracetam improved scopolamine-, bicuculline-, picrotoxin-, ethanol-, chlordiazepoxide- and cycloheximide-induced amnesia. Anti-amnesic action of nefiracetam on scopolamine model was antagonized by nifedipine and flunarizine, but not by diltiazem. Repeated administration of nefiracetam to AF64A-treated animals improved impairment of learning and memory as well as the alterations in cholinergic and monoaminergic neurotransmitters in the hippocampus. Basal forebrain (BF) lesioned rats induced by excitotoxin or by thermal coagulation showed impairment of learning accompanied by a marked reduction in choline acetyltransferase (ChAT) and acetylcholine esterase activities. Nefiracetam improved the learning deficit of the BF-lesioned rats. Nefiracetam also improved the carbon monoxide-induced delayed and acute amnesia. Nefiracetam stimulated acetylcholine release in the frontal cortex. Repeated administration of nefiracetam increased ChAT activity, gamma-aminobutyric acid (GABA) turnover and glutamic acid decarboxylase activity, and facilitated the Na(+)-dependent high-affinity GABA uptake. Nefiracetam activated the high voltage-activated (N/L-type) Ca2+ channel. The dose-response curves of nefiracetam were bell-shaped in both behavioral and biochemical studies. Therefore, it is suggested that nefiracetam improves the dysfunction of cholinergic, GABAergic and/or monoaminergic neuronal function by acting at Ca2+ channel and enhancing the release of neurotransmitters, and modifies impairment of memory processes induced by drugs and hypoxia.

Neuronal mechanisms mediating drug-induced cognition enhancement: cognitive activity as a necessary intervening variable

The conceptual foundations of a research aimed at the determination of potential neuronal, neuropharmacological, and behavioral/cognitive mechanisms mediating drug-induced cognition enhancement are discussed. The available evidence justifies a focus on attentional processes as a target for drug-induced cognition enhancement. Neuropharmacological mechanisms that may mediate drug-induced enhancement of attentional functions are proposed to interact necessarily with attention-associated neuronal activity. The elements of a transsynaptic approach to increase the excitability of basal forebrain cholinergic neurons and hence, attentional functions are discussed. Experimental tests of this hypothesis require the demonstration of interactions between cognition-induced increases in the activity of cortical cholinergic afferents and the effects of putative cognition enhancers. The available data illustrate that the effects of benzodiazepine receptor (BZR) agonists and inverse agonists on cortical acetylcholine (ACh) efflux interact with the state of activity in this system. The feasibility, potential heuristic power, and the experimental and conceptual problems of studies attempting to simultaneously assess drug effects on behavioral/cognitive abilities, ACh efflux, and neuronal activity have been revealed by an experiment intended to correlate performance in a task measuring sustained attention with medial prefrontal ACh efflux and medial prefrontal single-unit activity. The rational development of a psychopharmacology of cognition enhancers requires a union among behavioral/cognitive pharmacology, neuropharmacological and electrophysiological approaches.