Conformationally-restricted vigabatrin analogs as irreversible and reversible inhibitors of gamma-aminobutyric acid aminotransferase

Compounds that inhibit gamma-aminobutyric acid aminotransferase exhibit anticonvulsant activity; vigabatrin is a known irreversible inhibitor of this enzyme and anticonvulsant drug. Conformationally-restricted, five-membered- and six-membered-ring vigabatrin analogs were synthesized and tested as inhibitors of gamma-aminobutyric acid aminotransferase. Two monofluorinated compounds, 4 and 5, are time-dependent inhibitors of the enzyme, and their potencies are comparable to that of vigabatrin. Compounds 6 and 7 are weak reversible inhibitors.     

Acute anticonvulsant activity of structural analogues of valproic acid and changes in brain GABA and aspartate content

Ten analogues of valproic acid (substituted butyric, pentanoic and hexanoic acids) were tested for anticonvulsant activity against audiogenic seizures in DBA/2 mice. There is a consistent correlation between the structure of these branched-chain fatty acids and their anticonvulsant potency, the larger molecules being the more active. There is also a strong correlation between the anticonvulsant potency of these compounds and their ability to reduce cerebral aspartate levels. Cerebral GABA levels are elevated by most, but not all, of the actively anticonvulsant valproate analogues.     

Anticonvulsant activity of glycylglycine and delta-aminovaleric acid: evidence for glutamine exchange in amino acid transport

We have proposed that glutamine serves in a facilitated diffusion process, mediated by the enzyme gamma-glutamyl transferase (gamma-glutamyl transpeptidase; gamma GT) and that it leaves the brain in exchange for entering amino acids. Glutamine is also a precursor of gamma-aminobutyric acid (GABA). Thus, providing an alternate substrate for gamma GT should spare brain glutamine, raise GABA, and cause an anticonvulsant effect. We have found that glycylglycine, the best-known substrate for gamma GT, and delta-aminovaleric acid (DAVA), a structural analog, have anticonvulsant activity in DBA/2J mice. Both compounds can decrease the incidence and severity of seizures induced by L-methionine-RS-sulfoximine or electroconvulsive shock. DAVA was also tested and found to be active against seizures caused by pentylenetetrazol or picrotoxin. [14C]DAVA entered the brain at the rate of 18.7 nmol/g/min. The activity of DAVA as a substrate of gamma GT was intermediate to that of glycylglycine and glutamine. Preliminary studies have shown that brain glutamine and perhaps GABA are elevated 3 h after administration of DAVA (7.5 mmol/kg). These findings support the theory that glutamine exchange plays a role in amino acid transport across the blood-brain barrier and suggests a new concept in anticonvulsant therapy.     

New derivatives of picolinic acid and nicotinic acid with anticonvulsant activity

Previously obtained Pic-BZA is a potent anticonvulsant with low neurotoxicity, but its half-time of action is only about 15 min. In search for equally effective anticonvulsants but with a longer time of action fourteen Pic-BZA analogs were obtained. The compounds were evaluated in the Anticonvulsant Screening Project (ASP) of Antiepileptic Drug Development Program (ADDP) of NIH. Picolinic acid 2-fluorobenzylamide (Pic-2-F-BZA, 7) appeared to be the most effective compound of the series.     

Valproic acid extends Caenorhabditis elegans lifespan

Aging is an important biological phenomenon and a major contributor to human disease and disability, but no drugs have been demonstrated to delay human aging. Caenorhabditis elegans is a valuable model for studies of animal aging, and the analysis of drugs that extend the lifespan of this animal can elucidate mechanisms of aging and might lead to treatments for age-related disease. By testing drugs that are Food and Drug Administration approved for human use, we discovered that the mood stabilizer and anticonvulsant valproic acid (VA) extended C. elegans lifespan. VA also delayed age-related declines of body movement, indicating that VA delays aging. Valproic acid is a small carboxylic acid that is the most frequently prescribed anticonvulsant drug in humans. A structure-activity analysis demonstrated that the related compound valpromide also extends lifespan. Valproic acid treatment may modulate the insulin/IGF-1 growth factor signaling pathway, because VA promoted dauer larvae formation and DAF-16 nuclear localization. To investigate the mechanism of action of VA in delaying aging, we analyzed the effects of combining VA with other compounds that extend the lifespan of C. elegans. Combined treatment of animals with VA and the heterocyclic anticonvulsant trimethadione caused a lifespan extension that was significantly greater than treatment with either of these drugs alone. These data suggest that the mechanism of action of VA is distinct from that of trimethadione, and demonstrate that lifespan-extending drugs can be combined to produce additive effects.     

Brain anticonvulsant protection of mice given chronic carbamazepine under various fatty acid and magnesium diet conditions

The anticonvulsant and mood stabilizer drug carbamazepine (CBZ) was evaluated for anti-seizure activity after drug pretreatment of young weaning mice given various oil-based diets. These diets had various mono-(MUFA) and poly-(PUFA) unsaturated fatty acid contents, were associated or not with magnesium deprivation, and were given over the entire experimental period (34 days). The diets included a commercial and three purified synthetic diets (n-6 PUFA, n-3 PUFA and MUFA-based chows containing 5% corn/sunflower oils 1:3, 5% rapeseed oil and 5% high oleic acid sunflower oil/sunflower oil 7:3, respectively). A 10-days CBZ treatment (50mg/kg/day fragmented in two daily intraperitoneal injections of 25mg/kg) was given 20 days after initiating diet administration and evaluations of mice was performed 4 days after arrest of CBZ in various seizure tests. In these conditions, CBZ pretreatment still exhibited anticonvulsant protection especially in magnesium-deficient animals. Ethosuximide (ESM)-like profiles under MUFA and n-3 PUFA diets and unusual GABA(A)ergic profile under n-6 PUFA diet in magnesium-deficiency dependent audiogenic seizures (MDDAS) test as well as protection against NMDA-induced seizures in all lipid (n-3 PUFA>MUFA and n-6 PUFA) diet conditions were observed in CBZ-pretreated mice. By highlighting ESM-like and anti-NMDA mechanisms previously induced by an n-3 PUFA diet, present CBZ anticonvulsant properties suggest brain protective targets common to CBZ and n-3 PUFAs.     

Anticonvulsant effects of the 3-hydroxyanthranilic acid dioxygenase inhibitor NCR-631

Summary. The kynurenine pathway intermediate 3-hydroxyanthranilic acid (3-HANA) is converted by 3-HANA 3,4-dioxygenase (3-HAO) to the pro-convulsive excitotoxin quinolinic acid. In the present study, the anticonvulsant effect of the 3-HAO inhibitor NCR-631 was investigated in models of chemically- and sound-induced seizures. Administration of NCR-631 i.c.v. at a dose of 300 nmol in Sprague-Dawley rats was found to prolong the latency of occurrence of pentylenetetrazole (PTZ)-induced seizures. Also systemic pre-treatment with NCR-631 s.c. in N.M.R.I. mice subjected to PTZ-induced seizures provided an increase in the latency until onset of seizures, concomitant with a reduction in the severity of the seizures. However, the anticonvulsant effect of NCR-631 was short lasting (15–30 min), and only observed at a dose of 250 mg/kg. A similar dose- and time-dependent anticonvulsant effect of NCR-631 was found in seizure-prone DBA/2J mice following sound-induced convulsions. Hence, the findings show that NCR-631 has anticonvulsant properties against generalized tonic-clonic seizures of different origin, suggesting that it may constitute a useful tool to study the role of kynurenines in various convulsive states. Received August 31, 1999 Accepted September 20, 1999     

Bilobalide prevents reduction of gamma-aminobutyric acid levels and glutamic acid decarboxylase activity induced by 4-O-methylpyridoxine in mouse hippocampus

We previously reported that bilobalide, a constituent of Ginkgo biloba L. leaves, protected mice against convulsions induced by 4-O-methylpyridoxine (MPN). To elucidate the mechanism of the anticonvulsant activity of bilobalide, this study examined the effect of bilobalide on MPN-induced changes in the levels of gamma-aminobutyric acid (GABA) and glutamate, and in the activity of glutamic acid decarboxylase (GAD) in the hippocampus, cerebral cortex and striatum of the mouse. GABA levels and GAD activity in the hippocampus and cerebral cortex were significantly enhanced by bilobalide treatment (30 mg/kg, p.o., for 4 days) alone. MPN significantly decreased GABA levels and GAD activity in the three brain regions tested compared with those in the control. Pretreatment with bilobalide effectively suppressed the MPN-induced reduction in GABA levels and GAD activity in the hippocampus and cerebral cortex. On the other hand, there were no significant differences in the glutamate levels in the three regions despite various treatments. These results suggested that bilobalide prevents MPN-induced reduction in GABA levels through potentiation by bilobalide of GAD activity, and this effect of bilobalide contributes to its anticonvulsant effect against MPN-induced convulsions.     

Excavating precursors from the traditional Chinese herb Polygala tenuifolia and Gastrodia elata: Synthesis,anticonvulsant activity evaluation of 3,4,5-trimethoxycinnamic acid (TMCA) ester derivatives

Epilepsy is a group of neurological disorders characterized by recurrent seizures that disturbs about 60 million people worldwide. In this article, a novel series of 3,4,5-trimethoxycinnamic acid (TMCA) ester derivatives 1–35 were designed inspired from the traditional Chinese herb pair drugs Polygala tenuifolia and Gastrodia elata and synthesized followed by in vivo and in silico evaluation of their anticonvulsant potential. All the synthesized derivatives were biologically evaluated for their anticonvulsant potential using two acute model of seizures induced in mice, the maximal electroshock (MES) and sc-pentylenetetrazole (PTZ) models. Simultaneously, the motor impairment as a surrogate of acute neurotoxicity and in vitro screening of cytotoxicity against HepG-2 cells line were assessed through the rotarod performance test and CCK-8 assay, respectively. In addition, the physicochemical and pharmacokinetic parameters of the active compounds were determined. Our results showed that compounds 5, 7, 8, 13, 20, 25, 28, 30 and 32 exhibited preferable anticonvulsant activity in primary evaluation, with compounds 28 and 32 being the most promising anticonvulsant agents in according to results of subsequent pharmacology and toxicity evaluation. Additionally, the molecular modeling experiments predicted good binding interactions of part of the obtained active molecules with the gamma-aminobutyric acid (GABA) transferas. Therefore, it could be concluded that the synthesized derivatives 28 and 32 would represent useful lead compounds for further investigation in the development of anticonvulsant agents.     

Antagonism of intrastriatal and intravenous kainic acid by 1-nuciferine: Comparison with various anticonvulsants and gabamimetics

1-Nuciferine has been proposed as an antagonist of kainic acid (KA) and/or glutamate on the basis of iontophoretic experimental results. Its effectiveness against KA-induced destruction of rat striatal cholinergic neurons was therefore evaluated and compared with that of diazepam, phenobarbital, baclofen, haloperidol, and related substances. Drugs were administered intraperitoneally before and after intrastriatal microinjection of KA (0.5–1.5 μg), and choline acetyltransferase activity in striatum was assessed 24 hr later. Among the substances tested, only 1-nuciferine attenuated KA-induced depletions of striatal choline acetyltransferase. This effect was not secondary to anticonvulsant activity, because (a) 1-nuciferine did not block metrazol-, maximal electroshock-, or intravenous KA-induced seizures, and (b) anticonvulsants such as phenobarbital and diazepam, which are effective in these procedures, failed to modify KA-induced striatal neurotoxicity. 1-Nuciferine antagonized certain other neurological effects of intravenous KA, but antagonism was also seen with some of the other drugs tested. Intrastriatal microinjection of KA and/or glutamate may offer a means to detect selective antagonism of KA and/or glutamate, as distinguished from simple anticonvulsant activity.     

Effects of felbamate,kynurenic acid derivatives and nmda antagonists on in vitro kainate-induced epileptiform activity

The effects of the novel anticonvulsant felbamate, which binds to the 5–7 dichlorokynurenic binding sites, were tested towards the CA1 epileptiform activity induced in rat hippocampal slices by kainic acid. The effects of the kynurenic acid derivatives 7-chlorokynurenic acid and 5–7-dichlorokynurenic acid and of the NMDA antagonists COS 19755, MK-801 and ketamine were also studied for comparison. Slice perfusion with 1 μM kainic acid produced within 30 min the development of an evoked CA1 epileptiform bursting made up by an increase in amplitude of the primary population spikes followed by the appearance of secondary epileptiform population spikes. Slice perfusion with CGS 19755 (100 μM) or MK-801 (100 μM) or ketamine (100 μM) failed to affect within 30 min the CA1 epileptiform activity due to kainic acid. On the contrary, slice perfusion with felbamate (1.3–1.6 mM) or 7-chlorokynurenic acid (100 μM) or 5–7-dichlorokynurenic acid (100 μM) produced within 30 min a significative (P < 0.05) decrease of the kainate-induced epileptiform bursting duration. The results indicate that felbamate and kynurenic acid derivatives but not NMDA antagonists present an inhibitory effect against the epileptiform activity due to kainic acid.     

Modulation of benzodiazepine by lysine and pipecolic acid on pentylenetetrazol-induced seizures

L-lysine, an essential amino acid for man and animals, and its metabolite pipecolic acid (PA) have been studied for their effects on pentylenetetrazol (PTZ)-induced seizures in mice. L-Lysine or L-PA i.p. significantly increased clonic and tonic latencies in a dose-dependent manner against 90 mg/kg PTZ-induced seizures. L-Lysine but not L-PA enhanced the anticonvulsant effect of diazepam (DZ) (0.2 mg/kg). L-PA (0.1 mmol/kg) i.c.v. showed a slight decrease in clonic latency; it did not enhance the antiseizure activity of DZ; it caused seizures at 0.6 mmol/kg. D-PA (0.1 mmol/kg) i.c.v. displayed an opposite effect compared to its L-isomer. The anticonvulsant effect of L-lysine in terms of increase in seizure latency and survival was even more amplified when tested with a submaximal PTZ concentration (65 mg/kg). L-Lysine showed an enhancement of specific 3H-flunitrazepam (FZ) binding to mouse brain membranes both in vitro and in vivo. The possibility of L-lysine acting as a modulator for the GABA/benzodiazepine receptors was demonstrated. Since L-PA showed enhancement of 3H-FZ binding only in vitro but not in vivo, the anticonvulsant effect of L-PA may not be linked to the GABA/benzodiazepine receptor.     

Developmental toxicity of valproic acid

Valproic acid is a very effective anticonvulsant agent widely used in the management of various forms of epilepsy. Administration of the drug during pregnancy results in increased incidence of congenital abnormalities in both humans and experimental animals. In recent years, a significant number of research efforts have attempted to define the contributory role of valproic acid to the impairment of normal prenatal growth and development. The present report summarizes current knowledge that has emerged from clinical and research studies. The specific topics include: the placental transfer of valproic acid; the teratogenic potential; structure-teratogenicity and dose-response relationships; species and strain differences; biochemical changes evoked by the drug in the fetus.     

Effects of anticonvulsants and gamma-aminobutyric acid (GABA)-mimetic drugs on immunoreactive somatostatin and GABA contents in the rat brain

Immunoreactive somatostatin (IR-SRIF) and gamma-aminobutyric acid (GABA) contents in the rat brain were investigated to study chronic effects of the treatment with anticonvulsants, carbamazepine (CBZ), valproic acid (VPA) and phenytoin (PHT). Decreased IR-SRIF levels were found in several brain regions after chronic treatment with VPA and CBZ. GABA concentrations were found to be increased significantly in chronic CBZ and VPA treatment in the rat brain, especially in limbic structures. PHT had no effect on both IR-SRIF and GABA contents in the rat brain. Effects of several GABA-mimetic drugs also were studied on IR-SRIF contents in the rat brain. Aminooxyacetic acid an inhibitor of GABA transaminase, induced a decrease in IR-SRIF concentration in the pyriform and entorhinal cortex, whereas ethanolamine-o-sulfate, another GABA-transaminase inhibitor and muscimol, a GABA receptor agonist had no effect on brain IR-SRIF after acute administration. The present results suggest that endogenous somatostatin has an important role for anticonvulsant properties of CBZ and VPA, but not of PHT. The relationship between the changes in IR-SRIF and the GABA transmitter system in the anticonvulsant action of CBZ and VPA remains to be clarified.     

The effect of taurine on kindled seizures in the rat

Recently, it has been reported that taurine, an amino acid with anticonvulsant properties, does not suppress experimental seizures generated by the "kindling" technique. This finding seems somewhat paradoxical since taurine antagonizes other sorts of experimental convulsion and since kindled seizures are easily suppressed by other anticonvulsant drugs. Further tests were therefore conducted during which taurine's anticonvulsant effects were assessed: (1) when kindling stimulation was dropped to near-threshold levels; (2) when cortical as well as limbic kindled foci were stimulated; (3) when developing as well as fully kindled seizures were involved; and (4) when taurine was introduced directly into the ventricles of the brain. Even in these tests which were specifically designed to favour the appearance of anticonvulsant effects, no taurine antagonism of kindled seizures was found.     

Effect of a noncompetitive antagonist (MK-801) of NMDA receptors on convulsions and brain amino acid level in E1 mice

Anticonvulsant action of MK-801, a novel noncompetitive antagonist of N-methyl-d-aspartate (NMDA) receptor, was examined in genetically epileptic E1 mice. Systemic injection of MK-801 (0.1–1.0 mg/kg) potently suppressed generalized tonic-clonic convulsions of in a dose-dependent manner (ED₅₀, 0.17 mg/kg). This anticonvulsant effect of MK-801 appeared at a dose which did not induced any obvious behavioral changes. Following the administration of a fully anticonvulsant dose of MK-801 (1 mg/kg), amino acid analysis revealed a significantly elevated level of glycine in the hippocampus. Levels of other amino acids including glutamate, aspartate, taurine, glutamine, alanine, and -aminobutyrate were not changed either in the hippocampus or in the cerebral cortex. This study suggests that NMDA system may play an essential role in seizure-triggering mechanisms in E1 mouse.     

Convulsions induced by kynurenine and quinolinic acid as a sensitive test for assessing the anticonvulsant activity of GABA-ergic preparations

Phenibut, sodium hydroxybutyrate and baclofen are selectively effective against seizures induced in mice by the endogenous metabolites of tryptophan, L-kynurenine and quinolinic acid. The seizures were not affected by the drugs in doses under study. Depakine and aminooxyacetic acid as well as diazepam and phenobarbital appeared the most effective against pentylenetetrazole seizures. GABA and muscimol administered intracerebroventricularly merely prolonged the latency of seizures. Dissimilarities in the GABA-ergic mechanisms of the anticonvulsant effects of the drugs under consideration are discussed.     

Lack of attenuation of valproic acid-induced effects by folinic acid in rat embryos in vitro

The anticonvulsant drug valproic acid (VPA) is suspected to be a developmental toxicant in humans, inducing primarily neural tube defects. The mechanism for this effect is unknown, but it has been suggested that the drug may act via a deficiency of the vitamin folic acid. We examined this possibility by concurrent treatment of rat embryos in a whole embryo culture system with VPA and folinic acid (FA), a folic acid derivative. Groups of CD rat embryos were treated with various concentrations of VPA, various concentrations of FA, or a combination of a teratogenic dose of VPA plus various levels of FA. At the end of the 44 hour culture period, each embryo was evaluated for viability (presence of a heartbeat), yolk sac circulation, presence of any malformations, morphological score, crown-rump and head lengths, as well as DNA and protein contents. The anticonvulsant did not decrease viability but did decrease yolk sac circulation and all growth and developmental endpoints in a dose-responsive manner. There was also a dose-related increase in the incidence of open neural tubes. The addition of FA alone had no significant effect on growth and development. When various concentrations of FA were added simultaneously with a teratogenic dose of VPA, there was no decrease in the incidence of open neural tubes. Growth and developmental endpoints were altered in a somewhat random fashion but were never increased to the control level. The lack of attenuation by FA was not due to instability of the compound in the culture system, nor was there a difference in the amount of FA present in the exocoelomic fluid of VPA-treated and control embryos.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stereoselective synthesis of 2-amino-3-fluoro bicyclo[3.1.0]hexane-2,6-dicarboxylic acid.

(+)-2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY354740) is a conformationally restricted glutamate analogue that is a potent, selective and orally active group 2 metabotropic glutamate receptor agonist possessing anticonvulsant and anxiolytic properties. Herein, we describe a stereoselective and highly efficient synthesis of its 3-beta fluoro derivative using the Corey-Link methodology to create the amino acid stereogenic center.