Anticonvulsant drug action and regional neurotransmitter amino acid changes

The effect of valproate on the amino acids, monoamines, and kynurenic acid concentrations in brain structures involved in epileptogenesis in the pentylenetetrazol-kindled rats

BACKGROUND

The study aimed to assess the influence of a single valproate (VPA) administration on inhibitory and excitatory neurotransmitter concentrations in the brain structures involved in epileptogenesis in pentylenetetrazol (PTZ)-kindled rats.

METHODS

Adult, male Wistar rats were kindled by repeated intraperitoneal (ip) injections of PTZ at a subconvulsive dose (30 mg/kg, three times a week). Due to the different times required to kindle the rats (18-22 injections of PTZ), a booster dose of PTZ was administrated 7 days after the last rats were kindled. Then rats were divided into two groups: acute administration of VPA (400 mg/kg) or saline given ip. The concentration of amino acids, kynurenic acid (KYNA), monoamines, and their metabolites in the prefrontal cortex, hippocampus, amygdala, and striatum was assessed by high-pressure liquid chromatography (HPLC).

RESULTS

It was found that a single administration of VPA increased the gamma-aminobutyric acid (GABA), tryptophan (TRP), 5-hydroxyindoleacetic acid (5-HIAA), and KYNA concentrations and decreased aspartate (ASP) levels in PTZ-kindled rats in the prefrontal cortex, hippocampus, amygdala and striatum.

CONCLUSIONS

Our results indicate that a single administration of VPA in the PTZ-kindled rats restored proper balance between excitatory (decreasing the level of ASP) and inhibitory neurotransmission (increased concentration GABA, KYNA) and affecting serotoninergic neurotransmission in the prefrontal cortex, hippocampus, amygdala, and striatum.

A study of glutamate excitotoxicity in seizures related to tuberculous meningitis

BACKGROUND AND PURPOSE

Glutamate is a neurotransmitter that regulates approximately half of the nervous system, along with the sensory system. Glutamate excitotoxicity is related to seizures but its role in TBM-related seizure has not been reported to our best knowledge. It is proposed to report plasma glutamate level and its receptors in TBM patients with seizures and correlate with the type of seizures, Magnetic Resonance Imaging (MRI) findings, and outcome.

METHODS

TBM was diagnosed clinically with MRI as well as cerebrospinal fluid examination. TBM-related seizures have been categorized into early (< 1 month) or late (> 1 month) seizures. Six months outcome was defined using modified Rankin Scale as good (mRS ≤ 2) or poor (mRS > 2). Plasma glutamate was measured by ELISA, along with NR1, NR2A, and NR2B receptors using Real Time Polymerase Chain Reaction (RT-PCR) and have been correlated with seizure, MRI abnormalities, and outcome.

RESULTS

A total of 29 (53.7%) patients developed seizures (early-09, late-20). Glutamate (P < 0.0001), NR1 (p ≤ 0.0001), NR2A (p ≤ 0.0001), and NR2B (p ≤ 0.0001) were higher than the controls. In TBM patients with seizures, plasma glutamate (p = 0.01), NR1 (p = 0.03) and NR2A (p = 0.001) were significantly higher than those without seizures. Plasma glutamate level and all three receptor genes expression were higher during seizures and improved on cessation of seizure compared to the baseline. These markers correlated well with MRI findings and determined the outcome. ROC curve was used to estimate the diagnostic accuracy of the markers. The result indicated that NR2A gene was the best predictor followed by glutamate and NR1 gene.

CONCLUSION

Our results highlight the role of glutamate and its receptors in TBM-related seizures and outcomes.

Synthesis and biological evaluation of 2-phenoxyacetamide analogues, a novel class of potent and selective monoamine oxidase inhibitors

Monoamine oxidases (EC 1.4.3.4; MAOs), a family of FAD-containing enzymes, is an important target for antidepressant drugs. In this paper, a series of 2-phenoxyacetamide analogues were synthesized, and their inhibitory potency towards monoamine oxidases A (MAO-A) and B (MAO-B) were evaluated using enzyme and cancer cell lysate. 2-(4-Methoxyphenoxy)acetamide (compound 12) (SI = 245) and (2-(4-((prop-2-ynylimino)methyl)phenoxy)acetamide (compound 21) (IC_50MAO-A = 0.018 μM, IC_50MAO-B = 0.07 μM) were successfully identified as the most specific MAO-A inhibitor, and the most potent MAO-A/-B inhibitor, respectively. The inhibitory activities of these two compounds in living cells were also further evaluated utilizing HepG2 and SHSY-5Y cell lysates.

Fosinopril and zofenopril, two angiotensin-converting enzyme (ACE) inhibitors, potentiate the anticonvulsant activity of antiepileptic drugs against audiogenic seizures in DBA/2 mice

The renin-angiotensin system (RAS) exists in the brain and it may be involved in pathogenesis of neurological and psychiatric disorders including seizures. The aim of the present research was to evaluate the effects of some angiotensin-converting enzyme inhibitors (ACEi; captopril, enalapril, fosinopril and zofenopril), commonly used as antihypertensive agents, in the DBA/2 mice animal model of generalized tonic-clonic seizures. Furthermore, the co-administration of these compounds with some antiepileptic drugs (AEDs; carbamazepine, diazepam, felbamate, gabapentin, lamotrigine, phenobarbital, phenytoin, topiramate and valproate) was studied in order to identify possible positive interactions in the same model. All ACEi were able to decrease the severity of audiogenic seizures with the exception of enalapril up to the dose of 100mg/kg, the rank order of activity was as follows: fosinopril>zofenopril>captopril. The co-administration of ineffective doses of all ACE inhibitors with AEDs, generally increased the potency of the latter. Fosinopril was the most active in potentiating the activity of AEDs and the combination of ACEi with lamotrigine and valproate was the most favorable, whereas, the co-administrations with diazepam and phenobarbital seemed to be neutral. The increase in potency was generally associated with an enhancement of motor impairment, however, the therapeutic index of combined treatment of AEDs with ACEi was predominantly more favorable than control. ACEi administration did not influence plasma and brain concentrations of the AEDs studied excluding pharmacokinetic interactions and concluding that it is of pharmacodynamic nature. In conclusion, fosinopril, zofenopril, enalapril and captopril showed an additive anticonvulsant effect when co-administered with some AEDs, most notably carbamazepine, felbamate, lamotrigine, topiramate and valproate, implicating a possible therapeutic relevance of such drug combinations.

Quantitative genetics of sleep in inbred mice

The timing and the organization of sleep architecture are mainly controlled by the circadian system, while sleep need and intensity are regulated by a homeostatic process. How independent these two systems are in regulating sleep is not well understood. In contrast to the impressive progress in the molecular genetics of circadian rhythms, little is known about the molecular basis of sleep. Nevertheless, as summarized here, phenotypic dissection of sleep into its most basic aspects can be used to identify both the single major genes and small effect quantitative trait loci involved. Although experimental models such as the mouse are more readily amenable to genetic analysis of sleep, similar approaches can be applied to humans.

Species differences in the interactions of the anticonvulsant milacemide and some analogues with monoamine oxidase-B

Oxidation of the anticonvulsant drug milacemide [2-n-(pentylamino)acetamide] by monoamine oxidase-B (MAO-B) has been reported to be important in terminating its activity. Comparison of the oxidation of this compound by MAO-B preparations from ox and rat liver showed the former enzyme to have a significantly higher Km value towards this substrate. In keeping with this, the Ki values for milacemide acting as a competitive inhibitor of these enzymes showed it to have a lower affinity for ox liver MAO-B. Comparative studies on the time-dependent inhibition of the two enzymes also showed a lower sensitivity of that from the ox liver. Studies with a series of analogues involving replacement of pentylamino group of milacemide showed marked differences between the sensitivities of the two enzymes. The largest differences were shown by the compound 2(4-(3-chlorobenzoxy)phenethylamino)acetamide which gave IC50 values of 0.051 +/- 0.008 and 4.1 +/- 0.8 microM with the rat and ox enzymes, respectively, when activities were assayed without prior enzyme-inhibitor preincubation. When the enzyme and inhibitor were incubated for 60 min at 37 degrees before assay these values fell to 0.027 +/- 0.002 and 3.5 +/- 0.4 microM, respectively. These marked differences prompted a study of the inhibition of MAO-A and MAO-B from human liver and brain, mouse brain and rat brain as well as MAO-B from ox liver by milacemide and alpha-methylmilacemide. There were no significant differences in the sensitivities of any of the mitochondrial MAO-A preparations studied towards these compounds. However, MAO-B from human brain and liver mitochondrial resembled that from ox liver in being less sensitive to inhibition than the rat and mouse enzymes. Purification of the ox liver MAO-B did not significantly affect its interactions with milacemide and alpha-methylmilacemide. The marked species differences reported here raise questions concerning the validity of rodent model systems, that have frequently been used for assessing the in vivo and in vitro actions of milacemide and its analogues, for the situation in the human.

Interactions of some analogues of the anticonvulsant milacemide with monoamine oxidase

A series of analogues of the anticonvulsant drug milacemide (2-(n-pentylamino)-acetamide; Compound I) has been synthesized: 2-(benzylamino)acetamide (Compound II), 2-(phenethylamino)acetamide (Compound III), 2-(2-indol-3-yl)-ethylamino acetamide (Compound IV), 2-(2-(5-methoxyindol-3-yl)ethylamino)-acetamide (Compound V), 2-(2(4-chlorobenzamido)-ethylamino)acetamide (Compound VI), 2-(2-benzamidoethylamino)-acetamide (Compound VII) and 2-(4-(3-chlorobenzyloxy)phenethylamino)acetamide (Compound VIII). These compounds involve retention of the aminoacetamide portion of milacemide but replacement of the pentyl moiety with aromatic residues present in the structures of substrates and inhibitors of the monoamine oxidases. All the compounds tested were substrates for ox liver monoamine oxidase-B (MAO-B), producing an aldehyde that could act as a substrate for ox liver aldehyde dehydrogenase and H2O2 as a result of oxidative cleavage which also released glycinamide, although their Michaelis-Menten parameters differed markedly. None showed detectable activity as substrates for rat liver monoamine oxidase-A (MAO-A). Inhibition of the MAO-B by all the compounds except Compounds VIII and IV showed marked time dependence and was at least partly irreversible. There was no apparent change in the inhibition of MAO-A during enzyme-inhibitor preincubation at 37 degrees for 60 min. Compound VIII was a potent reversible inhibitor of both MAO-A and MAO-B (Ki = 2.8 +/- 0.1 and 4.1 +/- 0.8 microM), respectively. Comparison of the inhibitory potencies and the specificity constants of the series of compounds as substrates for MAO-B revealed no simple correlations with their anticonvulsant activities, as measured by their ability to prevent bicuculline-induced convulsions and death in the mouse. These results suggest that neither inhibition of MAO nor oxidative cleavage by this enzyme to yield glycinamide plays the major role in the anticonvulsant action of these compounds.

The interactions of milacemide with monoamine oxidase

The interactions of the anticonvulsant drug milacemide (2-n-pentylaminoacetamide) with rat liver mitochondrial monoamine oxidases-A and -B have been studied. The compound acts as a substrate for the B-form of the enzyme, with an apparent Km value of 49 +/- 4.7 microM and a Vmax value of 1.1 +/- 0.2 nmol/min/mg. It is also a time-dependent irreversible inhibitor of that enzyme. Any activity of monoamine oxidase-A towards this substrate was too low to allow accurate determinations to be made by either luminometric determination of H2O2 formation or spectrophotometric coupling of aldehyde formation to NAD+ reduction in the presence of aldehyde dehydrogenase. Milacemide was a reversible competitive inhibitor towards monoamine oxidase-A. The inhibitor constant (Ki) was 115 +/- 35 microM indicating a higher affinity than that towards monoamine oxidase-B, which was also competitively inhibited in the absence of enzyme-inhibitor preincubation (Ki = 331 +/- 185 microM). Determination of the formation of H2O2 and the aldehyde product of the oxidative cleavage of milacemide by purified monoamine oxidase-B from ox liver indicated that cleavage resulted solely in the formation of pentanal and glycinamide. There was no evidence for alternative cleavage to pentylamine and oxamaldehyde.

Milacemide therapy for Parkinson's disease

The clinical effects of central glutamatergic stimulation by the glycine prodrug milacemide were studied in six patients with Parkinson's disease under double-blind, placebo-controlled conditions. When administered as monotherapy at a single oral dose of 1,200 mg, the drug increased overall parkinsonian severity transiently, mostly due to an effect on rigidity. Milacemide did not, however, alter levodopa-induced dyskinesias. These results support the view that drugs acting on the glutamatergic system can influence motor function in patients with extrapyramidal movement disorders and that pharmaceutical agents that selectively block certain subtypes of glutamate receptors may ameliorate parkinsonian symptoms.

A rapid assay for neurotransmitter amino acids, aspartate, glutamate, glycine, taurine and ?-aminobutyric acid in the brain by high-performance liquid chromatography with electrochemical detection

For simultaneous assay of the five neurotransmitter amino acids, Asp, Glu, Gly, Tau, and GABA in brain tissues, a very rapid and simple chromatographic method using high-performance liquid chromatography with electrochemical detection in combination with o-phthalaldehyde derivatization is described. Because the present method permits the determination of these five amino acids within less than five minutes in one chromatographic run, up to 100 samples a working day can be analyzed using an autosampler. Within-run coefficients of variation for these five amino acids were less than 2% (n = 20). The quantitative detection limit was 2.5 pmol for the 5 amino acids. The present method has been applied to the measurement of the five amino acid neurotransmitter levels in several discrete brain regions of mice treated with and without electroconvulsive shock.

Is the oxidation of milacemide by monoamine oxidase a major factor in its anticonvulsant actions?

The anticonvulsant drug milacemide (2-n-pentylaminoacetamide) is known to be oxidized by monoamine oxidase-B to yield glycinamide which then breaks-down to give glycine. It has been postulated that it is this liberation of glycine in the brain that accounts for the anticonvulsant effects. In order to test this hypothesis, and since amines bearing a methyl-group in the alpha-position have been shown to be resistant to oxidation by monoamine oxidase, the effects of milacemide were compared with those of alpha-methyl-milacemide. Although the latter compound was found to be toxic at higher concentrations, it was found to antagonize bicuculline-induced convulsions in mice. When milacemide was administered to mice (0.5 mmol/kg, p.o.) there was a substantial increase in urinary glycinamide excretion. No such increase was observed after the administration of the same dose of alpha-methyl-milacemide. Furthermore, alpha-methyl-milacemide was not oxidized by either monoamine oxidase-A or -B in vitro to any detectable extent, although it was a competitive inhibitor of both forms of the enzyme. The findings that alpha-methyl-milacemide has anticonvulsant properties in the bicuculline test but is not a substrate for monoamine oxidase or a source of urinary glycinamide cast doubt on the importance of the oxidation or milacemide to form glycinamide as a major factor in its anticonvulsant action.

Very rapid and simple assay of taurine in the brain within two minutes by high-performance liquid chromatography with electrochemical detection

We describe a very rapid and simple method for the assay of taurine (Tau) in the brain tissue, using high-performance liquid chromatography (HPLC) with electrochemical detection in combination with precolumn o-phthalaldehyde (OPA) derivatization. The present method permits Tau assay within 2 min in one chromatographic run. Recovery for Tau was 107.4 +/- 1.3% (SD, n = 10). Within-run coefficients of variation were +/- 1.6% (n = 15). The limit of quantitative detection of the method was 0.1 pmol for Tau. The present method has been applied to the measurement of Tau levels in several discrete brain areas of the mouse.

MAO activity, metabolism and anticonvulsant activity of milacemide in rats and mice

Milacemide was found to protect Swiss albino CD1 mice but not Sprague Dawley rats against bicuculline-induced lethality. Since it had been previously suggested that the anticonvulsant activity of milacemide might be related to MAO-B- mediated glycine formation, brain and liver MAO-A and-B activities and the urinary metabolic pattern of milacemide were determined in the same mice and rat strains. Similar brain and liver MAO activities were found in the two species, except for liver MAO-A activity which was higher in rats. After the same oral dose of milacemide, the percent of the dose excreted as glycinamide was significantly higher in mice than in rats, whereas that excreted as metabolite UK1 was significantly higher in rats. These results support the hypothesis of a glycine-mediated anticonvulsant activity for milacemide and suggest that the increased formation of UK1 to the detriment of glycinamide might account for the lack of protection against bicuculline-induced lethality by milacemide in rats.

Beta-DL-methylene-aspartate, an inhibitor of aspartate aminotransferase, potently inhibits L-glutamate uptake into astrocytes

[3H]Glutamate uptake into astrocytes in primary culture was potently inhibited by the aspartate analogues L- and D-aspartic acid, DL-threo-beta-hydroxy-aspartic acid-beta-hydroxymate (IC50's: 136, 259, 168, and 560 microM, respectively) and by beta-DL-methylene-aspartate, a suicide inhibitor of aspartate aminotransferase (IC50: 524 microM), and by the endogenous sulphur-containing amino acid L-cysteinesulfinic acid (IC50: 114 microM), [3H]Glutamate uptake was not significantly affected by either N-methyl-D-aspartate or DL-homocysteine thiolactone. These results demonstrate that other excitatory amino acids including aspartate and L-cysteinesulfinic acid (but excluding L-homocysteic acid) interact with the glutamate transport system of astrocytes. Inhibition of glutamate uptake may significantly increase the level of neuronal excitability.