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

Antiepileptogenic Effects of Anakinra, Lamotrigine and Their Combination in a Lithium-Pilocarpine Model of Temporal Lobe Epilepsy in Rats

Temporal lobe epilepsy is a common, chronic disorder with spontaneous seizures that is often refractory to drug therapy. A potential cause of temporal lobe epilepsy is primary brain injury, making prevention of epileptogenesis after the initial event an optimal method of treatment. Despite this, no preventive therapy for epilepsy is currently available. The purpose of this study was to evaluate the effects of anakinra, lamotrigine, and their combination on epileptogenesis using the rat lithium-pilocarpine model of temporal lobe epilepsy. The study showed that there was no significant difference in the number and duration of seizures between treated and untreated animals. However, the severity of seizures was significantly reduced after treatment. Anakinra and lamotrigine, alone or in combination, significantly reduced neuronal loss in the CA1 hippocampus compared to the control group. However, the drugs administered alone were found to be more effective in preventing neuron loss in the hippocampal CA3 field compared to combination treatment. The treatment alleviated the impairments in activity level, exploratory behavior, and anxiety but had a relatively weak effect on TLE-induced impairments in social behavior and memory. The efficacy of the combination treatment did not differ from that of anakinra and lamotrigine monotherapy. These findings suggest that anakinra and lamotrigine, either alone or in combination, may be clinically useful in preventing the development of histopathological and behavioral abnormalities associated with epilepsy.

Zinc signaling and epilepsy

Evidence from both preclinical and clinical studies suggest the importance of zinc homeostasis in seizures/epilepsy. Undoubtedly, zinc, via modulation of a variety of targets, is necessary for maintaining the balance between neuronal excitation and inhibition, while an imbalance between excitation and inhibition underlies seizures. However, the relationship between zinc signaling and seizures/epilepsy is complex as both extracellular and intracellular zinc may produce either protective or detrimental effects. This review provides an overview of preclinical/behavioral, functional and molecular studies, as well as clinical data on the involvement of zinc in the pathophysiology and treatment of seizures/epilepsy. Furthermore, the potential of targeting elements associated with zinc signaling or homeostasis and zinc levels as a therapeutic strategy for epilepsy is discussed.

Effect of lamotrigine on seizure development in a rat pentylenetetrazole kindling model

INTRODUCTION

Epileptogenesis is a process of seizure development. Lamotrigine is a novel antiepileptic drug which is also used for antiepileptogenic research. Kindling models are recommended as potentially useful tools for antiepileptogenic treatment discovery. However, previous studies demonstrated that the antiepileptogenic effect of lamotrigine is controversial in the electrical kindling model. Chemical kindling such as with pentylenetetrazole is another kindling model. The aims of this study were to examine whether lamotrigine could prevent the development of seizure in pentylenetetrazole kindling rats.

METHODS

Female rats were kindled by subconvulsive doses of pentylenetetrazole (35 mg/kg) once every other day for 15 times. Thereafter, the kindled rats received different doses of lamotrigine (5, 10 and 20 mg/kg) before pentylenetetrazole to observe the anticonvulsant effect. For the antiepileptogenic experiment, rats were kindled as the same way while pretreated (1 h) with different doses of lamotrigine (5, 10 and 20 mg/kg) before each injection of pentylenetetrazole. After a washout period for 1 week, the rats were administrated with pentylenetetrazole again for 3 times. The seizures were recorded each time. Later it was in vivo electrophysiological experiments followed with histologic analysis.

RESULTS

For the anticonvulsant experiment lamotrigine dose-dependently suppressed pentylenetetrazole-induced seizures. Here, 20 mg/kg of lamotrigine pretreatment significantly blocked the seizure development in rats for their seizure stages remained longer in 1-3 during the kindling phase. Mean seizure stages or generalized seizure durations in the 10 and 20 mg/kg lamotrigine pretreated groups were significantly lower or shorter when received 3 times of pentylenetetrazole after the washout period. Electrophysiological study also demonstrated 20 mg/kg of lamotrigine pretreatment obviously eliminated increased population spike amplitude in hippocampus. However, different doses of lamotrigine pretreatment could not alleviate severity of hippocampal neuronal damage.

CONCLUSIONS

The results suggest that adequate doses of lamotrigine can prevent seizure development in the pentylenetetrazole kindling rat model.

Lamotrigine as monotherapy in clinical practice: efficacy of various dosages in epilepsy

OBJECTIVES/AIMS

The study was designed to evaluate the optimal dosage of lamotrigine, as monotherapy, in the treatment of adults suffering from complex partial seizures with or without secondary generalization in everyday clinical practice.

MATERIALS AND METHODS

The ones used in this study was the collection of the data of all adult patients treated with lamotrigine, retrospectively. The dosage and efficacy of treatment were evaluated along with side effects and retention rate.

RESULTS

They showed that, out of 188 patients, 77% continued lamotrigine treatment; the mean effective dose was 250 mg or higher of lamotrigine, and the results more pronounced in older patients (age above 30 years) and those with a longer disease duration (5 years and more).

CONCLUSION

It may be appropriate to reach a daily lamotrigine dose above 250 mg in adult patients suffering from epilepsy for more than 5 years using lamotrigine as monotherapy.

Post-status epilepticus treatment with the cannabinoid agonist WIN 55,212-2 prevents chronic epileptic hippocampal damage in rats

Repeated seizures are often associated with development of refractory chronic epilepsy, the most common form of which is temporal lobe epilepsy. G-protein-coupled cannabinoid receptors (CB1 and CB2 receptors) regulate neuronal excitability and have been shown to mediate acute anticonvulsant effects of cannabinoids in animal models. However, the potential of cannabinoids to prevent chronic neuronal damage and development of epilepsy remains unexplored. We hypothesized that treatment with a CB receptor agonist after an episode of status epilepticus--but before development of spontaneous recurrent seizures--might prevent the development of functional changes that lead to chronic epilepsy. Using the rat pilocarpine model, a therapeutic approach was simulated by administering the CB agonist, WIN 55,212-2 after an episode of status epilepticus. Epileptic behavior was monitored during development of spontaneous recurrent seizures for up to 6 months. Histology, neurochemistry, redox status and NMDA receptor subunit expression were assessed at 6 months after pilocarpine-induced seizures. Sub-acute treatment with WIN 55,212-2 (for 15 days starting 24h after PILO injection) dramatically attenuated the severity, duration and frequency of spontaneous recurrent seizures. Further, in contrast to vehicle-treated animals, hippocampi from WIN 55,212-2-treated animals showed: normal thiol redox state, normal NR2A and NR2B subunit expression, preservation of GABAergic neurons and prevention of abnormal proliferation of GABAergic progenitors. This study shows for the first time that, after a known inciting event, treatment with a compound targeting CB receptors has the potential to prevent the epileptogenic events that result in chronic epileptic damage.

Antiepileptic activity of preferential inhibitors of persistent sodium current

OBJECTIVE

Evidence from basic neurophysiology and molecular genetics has implicated persistent sodium current conducted by voltage-gated sodium (NaV ) channels as a contributor to the pathogenesis of epilepsy. Many antiepileptic drugs target NaV channels and modulate neuronal excitability, mainly by a use-dependent block of transient sodium current, although suppression of persistent current may also contribute to the efficacy of these drugs. We hypothesized that a drug or compound capable of preferential inhibition of persistent sodium current would have antiepileptic activity.

METHODS

We examined the antiepileptic activity of two selective persistent sodium current blockers ranolazine, a U.S. Food and Drug Administration (FDA)-approved drug for treatment of angina pectoris, and GS967, a novel compound with more potent effects on persistent current, in the epileptic Scn2a(Q54) mouse model. We also examined the effect of GS967 in the maximal electroshock model and evaluated effects of the compound on neuronal excitability, propensity for hilar neuron loss, development of mossy fiber sprouting, and survival of Scn2a(Q54) mice.

RESULTS

We found that ranolazine was capable of reducing seizure frequency by approximately 50% in Scn2a(Q54) mice. The more potent persistent current blocker GS967 reduced seizure frequency by >90% in Scn2a(Q54) mice and protected against induced seizures in the maximal electroshock model. GS967 greatly attenuated abnormal spontaneous action potential firing in pyramidal neurons acutely isolated from Scn2a(Q54) mice. In addition to seizure suppression in vivo, GS967 treatment greatly improved the survival of Scn2a(Q54) mice, prevented hilar neuron loss, and suppressed the development of hippocampal mossy fiber sprouting.

SIGNIFICANCE

Our findings indicate that the selective persistent sodium current blocker GS967 has potent antiepileptic activity and that this compound could inform development of new agents.

Certain secondary antiepileptic drugs can rescue hippocampal injury following a critical growth period despite poor anticonvulsant activity and cognitive deficits

Clinical and experimental studies have shown that many common secondary antiepileptic drugs (AEDs) are ineffective at blocking seizures in adulthood; however, some afford neuroprotection. In early development, certain AEDs cause apoptosis; however, it is unknown whether these drugs are neurotoxic to the juvenile brain following a developmentally regulated proapoptotic period and whether they alter the seizure threshold, seizure-induced neuronal vulnerability, and/or cognitive function. Lamotrigine (LTG), carbamazepine (CBZ), phenytoin (PHT), valproate (VPA), and topiramate (TPM) were systemically administered to rat pups for 7days beginning on postnatal (P) day 14 (P14), then half the animals were injected with kainate (KA) to trigger seizures, an age when the CA1 subregion becomes preferentially sensitive to status epilepticus. Histological outcome, seizure severity, and learning and memory were determined with an electroencephalograph (EEG), silver impregnation, and a water-maze swim task. None of the AEDs tested significantly attenuated behavioral or electrographic seizures. Phenytoin increased mortality, identifying a detrimental side effect of this drug. The other drugs (LTG, VPA, TPM, and CBZ) afforded different amounts of protection to the CA1 subregion but not to the CA3 subregion or extrahippocampal structures. With the exception of VPA, AED-treated animals lagged behind during swim task acquisition. All groups improved in the water-maze swim task over time, particularly on the last trials; however, the average escape latency was still impaired for TPM-treated animals and all AED+KA-treated groups. Thus, while certain AEDs demonstrated some neuroprotective effects, poor antiepileptic activity, memory impairment, and other deleterious side effects were observed with these drugs suggesting that the search for potentially more effective and tolerated agents is essential for improving clinical outcome in children and adolescents with epilepsy.

Prevention or modification of epileptogenesis after brain insults: experimental approaches and translational research

Diverse brain insults, including traumatic brain injury, stroke, infections, tumors, neurodegenerative diseases, and prolonged acute symptomatic seizures, such as complex febrile seizures or status epilepticus (SE), can induce "epileptogenesis," a process by which normal brain tissue is transformed into tissue capable of generating spontaneous recurrent seizures. Furthermore, epileptogenesis operates in cryptogenic causes of epilepsy. In view of the accumulating information about cellular and molecular mechanisms of epileptogenesis, it should be possible to intervene in this process before the onset of seizures and thereby either prevent the development of epilepsy in patients at risk or increase the potential for better long-term outcome, which constitutes a major clinical need. For identifying pharmacological interventions that prevent, interrupt or reverse the epileptogenic process in people at risk, two groups of animal models, kindling and SE-induced recurrent seizures, have been recommended as potentially useful tools. Furthermore, genetic rodent models of epileptogenesis are increasingly used in assessing antiepileptogenic treatments. Two approaches have been used in these different model categories: screening of clinically established antiepileptic drugs (AEDs) for antiepileptogenic or disease-modifying potential, and targeting the key causal mechanisms that underlie epileptogenesis. The first approach indicated that among various AEDs, topiramate, levetiracetam, carisbamate, and valproate may be the most promising. On the basis of these experimental findings, two ongoing clinical trials will address the antiepileptogenic potential of topiramate and levetiracetam in patients with traumatic brain injury, hopefully translating laboratory discoveries into successful therapies. The second approach has highlighted neurodegeneration, inflammation and up-regulation of immune responses, and neuronal hyperexcitability as potential targets for antiepileptogenesis or disease modification. This article reviews these areas of progress and discusses the challenges associated with discovery of antiepileptogenic therapies.

Disease-modifying activity of progesterone in the hippocampus kindling model of epileptogenesis

Progesterone (P) is an endogenous anticonvulsant hormone. P is being evaluated as a treatment for epilepsy, traumatic brain injury, and other complex neurological conditions. Preclinical and clinical studies suggest that P appears to interrupt epileptogenic events. However, the potential disease-modifying effect of P in epileptogenic models is not widely investigated. In this study, we examined the effects of P on the development of hippocampus kindling in female mice. In addition, we determined the role of progesterone receptors (PR) in the P's effect on the kindling epileptogenesis utilizing PR knockout (PRKO) mice. P, at 25 mg/kg, did not affect seizures and did not exert sedative/motor effects in fully-kindled mice. P treatment (25 mg/kg, twice daily for 2 weeks) significantly suppressed the rate of development of behavioral kindled seizure activity evoked by daily hippocampus stimulation in wild-type (WT) mice, indicating a disease-modifying effect of P on limbic epileptogenesis. There was a significant increase in the rate of 'rebound or withdrawal' kindling during drug-free stimulation sessions following abrupt discontinuation of P treatment. A washout period after termination of P treatment prevented such acceleration in kindling. PRKO mice were kindled significantly slower than WT mice, indicating a modulatory role of PRs in seizure susceptibility. P's effects on early kindling progression was partially decreased in PRKO mice, but the overall (˜2-fold) delay in the rate of kindling for the induction of stage 5 seizures was unchanged in PRKO mice. Moreover, the acute anticonvulsant effect of P was undiminished in fully-kindled PRKO mice. These studies suggest that P exerts disease-modifying effects in the hippocampus kindling model at doses that do not significantly affect seizure expression and motor performance, and the kindling-retarding effects of P may occur partly through a complex PR-dependent and PR-independent mechanism.

Evaluation of development-specific targets for antiepileptogenic therapy using rapid kindling

We used the method of rapid hippocampal kindling to assess the potential antiepileptogenic efficacy of a number of anticonvulsant medications. This method afforded a higher throughput than methods based on traditional kindling or post-status epilepticus models of epileptogenesis. This "compressed epileptogenesis" model also permitted the study of age-dependent pharmacologic targets, and distinguished among antiepileptic drugs (AEDs) on the basis of their age-specific antiepileptogenic efficacy. We found retigabine to be the most effective anticonvulsant therapy during early development. Topiramate seemed most effective further along development, whereas some drugs did not demonstrate an age-specific effect. The method also reproduced some of the paradoxical pharmacologic findings previously shown with lamotrigine. Although the utility of this model for screening the antiepileptogenic therapies requires further validation, it introduces the ability to undertake development-specific testing and a more rapid throughput than conventional methods.

Effects of lamotrigine and topiramate on hippocampal neurogenesis in experimental temporal-lobe epilepsy

Lamotrigine (LTG) and topiramate (TPM), two of the most commonly used new-generation antiepileptic drugs (AEDs), have been shown to produce no adverse and impaired cognitive effects in patients with epilepsy, respectively. As seizure-induced neurogenesis might contribute to cognitive deficits that are associated with status epilepticus (SE), we examined whether these two drugs produce differential effects on seizure-induced neurogenesis in the hippocampus of adult rats. Lithium pilocarpine model was used to mimic human temporal-lobe epilepsy. Five hours after SE, LTG and TPM were administered intragastrically twice daily throughout the entire length of the experiment with total daily dose of 20 and 80 mg/kg, respectively. The hippocampal neurogenesis was examined using 5-bromodeoxyuridine and doublecortin immunohistochemistry. Both LTG and TPM treatments significantly inhibited seizure-induced proliferation of neural progenitors in the hippocampus, but did not affect the neuronal differentiation of newborn cells. Long-term treatment with both AEDs decreased the number of spontaneous recurrent seizures after SE and alleviated chronic seizure-induced neuronal injury in the dentate hilus. Eventually, TPM significantly increased the number of newborn neurons in the dentate granular cell layer after seizures likely by promoting the survival of newborn neurons. In contrast, LTG treatment significantly reduced the number of ectopic hilar newborn neurons after seizures. Neither of them prevented the formation of hilar basal dendrites of newborn neurons in the epileptic hippocampus. These results indicate that TPM but not LTG promotes aberrant neuron regeneration in the hippocampus after SE, which might be partially related to their differential effects on cognitive function.

Pursuing paradoxical proconvulsant prophylaxis for epileptogenesis

There are essentially two potential treatment options for any acquired disorder: symptomatic or prophylactic. For acquired epilepsies that follow a variety of different brain insults, there remains a complete lack of prophylactic treatment options, whereas at the same time these epilepsies are notoriously resistant, once they have emerged, to symptomatic treatments with antiepileptic drugs. The development of prophylactic strategies is logistically challenging, both for basic researchers and clinicians. Nevertheless, cannabinoid-targeting drugs provide a very interesting example of a system within the central nervous system (CNS) that can have very different acute and long-term effects on hyperexcitability and seizures. In this review, we outline research on cannabinoids suggesting that although cannabinoid antagonists are acutely proconvulsant, they may have beneficial effects on long-term hyperexcitability following brain insults of multiple etiologies, making them promising candidates for further investigation as prophylactics against acquired epilepsy. We then discuss some of the implications of this finding on future attempts at prophylactic treatments, specifically, the very short window within which prevention may be possible, the possibility that traditional anticonvulsants may interfere with prophylactic strategies, and the importance of moving beyond anticonvulsants-even to proconvulsants-to find the ideal preventative strategy for acquired epilepsy.

Antiepileptogenic and antiictogenic effects of retigabine under conditions of rapid kindling: an ontogenic study

PURPOSE

To examine antiepileptogenic and antiictogenic potential of retigabine (RTG) under conditions of rapid kindling epileptogenesis during different stages of development.

METHODS

The experiments were performed in postnatal day 14 (P14), P21, and P35 male Wistar rats. After stereotaxic implantation of hippocampal stimulating and recording electrodes, the effects of RTG on baseline afterdischarge (AD) properties were studied. Next, the animals underwent rapid kindling (sixty 10 s trains, bipolar 20 Hz square wave pulses delivered every 5 min). The progression of seizures (kindling acquisition), and responses to test stimulations after kindling (retention) were compared between RTG and vehicle-treated rats. Additionally, the effects of RTG on the severity of seizures in previously kindled animals were examined.

RESULTS

When administered intraperitoneally in doses that induced only mild, or no motor deficits, RTG significantly dampened brain excitability, evident as the increase of AD threshold and shortening of AD duration. During kindling, RTG delayed the development of focal seizures in P14 rats, and prevented the occurrence of full limbic seizures at all three ages. At P14 and P21, but not at P35, pretreatment with RTG prevented the establishment of kindling-induced enhanced seizure susceptibility. Administration of RTG to kindled animals decreased the severity of seizures induced by test stimulation. The effect was most prominent at P14.

DISCUSSION

RTG exerted both antiepileptogenic and antiictogenic effects under conditions of rapid kindling model. These effects were apparent during postneonatal, early childhood, and adolescent stages of development.

Modulatory effects of nitric oxide-active drugs on the anticonvulsant activity of lamotrigine in an experimental model of partial complex epilepsy in the rat

Background

The effects induced by administering the anticonvulsant lamotrigine, the preferential inhibitor of neuronal nitric oxide synthase 7-nitroindazole and the precursor of NO synthesis L-arginine, alone or in combination, on an experimental model of partial complex seizures (maximal dentate gyrus activation) were studied in urethane anaesthetized rats. The epileptic activity of the dentate gyrus was obtained through the repetitive stimulation of the angular bundle and maximal dentate gyrus activation latency, duration and post-stimulus afterdischarge duration were evaluated.

Results

Either Lamotrigine (10 mg kg^-1) or 7-nitroindazole (75 mg kg^-1) i.p. administration had an anticonvulsant effect, significantly reducing the number of animals responding to angular bundle stimulation. On the contrary, i.p. injection of L-arginine (1 g kg^-1) induced an aggravation of the epileptiform phenomena, demonstrated by the significant augmentation of the duration of both maximal dentate activation and afterdischarge. Furthermore, the injection of lamotrigine and 7-nitroindazole in combination significantly increased the anticonvulsant effects induced by the same drugs separately, either reducing the number of responding animals or decreasing both maximal dentate gyrus activation and afterdischarge durations. On the contrary, the combined treatment with L-arginine and lamotrigine did not modify the maximal dentate gyrus activation parameters suggesting an adversative effect of L-arginine-increased nitric oxide levels on the lamotrigine-induced anticonvulsant action.

Conclusion

The present results indicate that the nitrergic neurotransmission exerts a significant modulatory role in the control of the development of paroxystic phenomena in the maximal dentate gyrus activation model of epilepsy. Finally, our data suggest a functional relationship between the nitric oxide system and the anticonvulsant effect of lamotrigine which could be enhanced by reducing nitric oxide levels and, conversely, dampened by an increased nitrergic activity.

Increased expression of caspase 2 in experimental and human temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is often caused by a neurodegenerative brain insult that triggers epileptogenesis, and eventually results in spontaneous seizures, i.e., epilepsy. Understanding the mechanisms of cell death is a key for designing new drug therapies for preventing the neurodegeneration associated with TLE. Here, we investigated the expression of caspase 2, a protein involved in programmed cell death, during the course of epilepsy. We investigated caspase 2 expression in hippocampal samples derived from patients operated on for drug refractory TLE. To understand the evolution of altered-caspase 2 expression during the epileptic process, we also examined caspase 2 expression and activity in the rat hippocampus after status epilepticus-induced acute damage, during epileptogenesis, and after the onset of epilepsy. Caspase 2 expression was enhanced in the hippocampal neurons in chronic TLE patients. In rats, status epilepticus-induced caspase 2 labeling paralleled the progression of neurodegeneration. Proteolytic activation and cleavage of caspase 2 was also detected in the rat brain undergoing epileptogenesis. Our data suggest that caspase 2-mediated programmed cell death participates in the seizure-induced degenerative process in experimental and human TLE.

Manganese-enhanced magnetic resonance imaging of mossy fiber plasticity in vivo

Mn(2+)-enhanced magnetic resonance imaging (MEMRI) was used to characterize activity-dependent plasticity in the mossy fiber pathway after intraperitoneal kainic acid (KA) injection. Enhancement of the MEMRI signal in the dentate gyrus and the CA3 subregion of the hippocampus was evident 3 to 5 days after injection of MnCl(2) into the entorhinal cortex both in control and KA-injected rats. In volume-rendered three-dimensional reconstructions, Mn(2+)-induced signal enhancement revealed the extent of the mossy fiber pathway throughout the septotemporal axis of the dentate gyrus. An increase in the number of Mn(2+)-enhanced pixels in the dentate gyrus and CA3 subfield of rats with KA injection correlated (P < 0.05) with histologically verified mossy fiber sprouting. These data demonstrate that MEMRI can be used to detect specific changes at the cellular level during activity-dependent plasticity in vivo. The present findings also suggest that MEMRI signal changes can serve as an imaging marker of epileptogenesis.

Caspase 6 expression in the rat hippocampus during epileptogenesis and epilepsy

The molecular basis of neuronal circuit reorganization during epileptogenesis is poorly understood. Such data are, however, critical for the search of new targets for the prevention of epileptogenesis. Here, we extended our previous studies on caspases in epileptogenesis by investigating the expression and activity of caspase 6 at different phases of the epileptic process in rats. Epileptogenesis was triggered by kainate-induced status epilepticus (SE) under video-electroencephalography-monitoring. Caspase 6 activity was measured fluorometrically in the hippocampus 8 h, 24 h, 48 h, 1 week, and 4 weeks after SE. Caspase 6 expression was examined using Western blot and immunohistochemistry. Our data demonstrated that the SE-induced increase in the expression of cleaved caspase 6 and its intraneuronal localization were dependent on the time delay from SE induction. Double-labeling with a neuronal marker, NeuN, indicated that within the first 48 h, caspase 6 immunoreactivity was present both in the hippocampal pyramidal cells and hilar neurons, some of which were also terminal transferase dUTP-end labeling-positive. This was coincident with a transient 18-fold increase in caspase 6 enzymatic activity. At the 1-week and 4-week time points, elevated caspase 6 immunoreactivity was detected in the dendritic processes and neuropil. These findings indicate that caspase 6 expression remains elevated long after the occurrence of acute cell death during epileptogenesis and epilepsy. Further, caspase 6 protein is not exclusively located in the somata of neurons, but also in dendrites. These data suggest that caspase 6 has functions other than execution of programmed cell death in epileptogenic hippocampus.