Genetically engineered GABA-producing cells demonstrate anticonvulsant effects and long-term transgene expression when transplanted into the central piriform cortex of rats

Present in the Aquatic Environment, Unclear Evidence in Top Predators-The Unknown Effects of Anti-Seizure Medication on Eurasian Otters (Lutra lutra) from Northern Germany

Emerging contaminants are produced globally at high rates and often ultimately find their way into the aquatic environment. These include substances contained in anti-seizure medication (ASM), which are currently appearing in surface waters at increasing concentrations in Germany. Unintentional and sublethal, chronic exposure to pharmaceuticals such as ASMs has unknown consequences for aquatic wildlife. Adverse effects of ASMs on the brain development are documented in mammals. Top predators such as Eurasian otters (Lutra lutra) are susceptible to the bioaccumulation of environmental pollutants. Still little is known about the health status of the otter population in Germany, while the detection of various pollutants in otter tissue samples has highlighted their role as an indicator species. To investigate potential contamination with pharmaceuticals, Eurasian otter brain samples were screened for selected ASMs via high-performance liquid chromatography and mass spectrometry. Via histology, brain sections were analyzed for the presence of potential associated neuropathological changes. In addition to 20 wild otters that were found dead, a control group of 5 deceased otters in human care was studied. Even though none of the targeted ASMs were detected in the otters, unidentified substances in many otter brains were measured. No obvious pathology was observed histologically, although the sample quality limited the investigations.

Clocking Epilepsies: A Chronomodulated Strategy-Based Therapy for Rhythmic Seizures

Epilepsy is a neurological disorder characterized by hypersynchronous recurrent neuronal activities and seizures, as well as loss of muscular control and sometimes awareness. Clinically, seizures have been reported to display daily variations. Conversely, circadian misalignment and circadian clock gene variants contribute to epileptic pathogenesis. Elucidation of the genetic bases of epilepsy is of great importance because the genetic variability of the patients affects the efficacies of antiepileptic drugs (AEDs). For this narrative review, we compiled 661 epilepsy-related genes from the PHGKB and OMIM databases and classified them into 3 groups: driver genes, passenger genes, and undetermined genes. We discuss the potential roles of some epilepsy driver genes based on GO and KEGG analyses, the circadian rhythmicity of human and animal epilepsies, and the mutual effects between epilepsy and sleep. We review the advantages and challenges of rodents and zebrafish as animal models for epileptic studies. Finally, we posit chronomodulated strategy-based chronotherapy for rhythmic epilepsies, integrating several lines of investigation for unraveling circadian mechanisms underpinning epileptogenesis, chronopharmacokinetic and chronopharmacodynamic examinations of AEDs, as well as mathematical/computational modeling to help develop time-of-day-specific AED dosing schedules for rhythmic epilepsy patients.

Mechanisms of pallidal deep brain stimulation: Alteration of cortico-striatal synaptic communication in a dystonia animal model

Pallidal deep brain stimulation (DBS) is an important option for patients with severe dystonias, which are thought to arise from a disturbance in striatal control of the globus pallidus internus (GPi). The mechanisms of GPi-DBS are far from understood. Although a disturbance of striatal function is thought to play a key role in dystonia, the effects of DBS on cortico-striatal function are unknown. We hypothesised that DBS, via axonal backfiring, or indirectly via thalamic and cortical coupling, alters striatal function. We tested this hypothesis in the dtsz hamster, an animal model of inherited generalised, paroxysmal dystonia. Hamsters (dystonic and non-dystonic controls) were bilaterally implanted with stimulation electrodes in the GPi. DBS (130 Hz), and sham DBS, were performed in unanaesthetised animals for 3 h. Synaptic cortico-striatal field potentials, as well as miniature excitatory postsynaptic currents (mEPSC) and firing properties of medium spiny striatal neurones were recorded in brain slice preparations obtained immediately after EPN-DBS. The main findings were as follows: a. DBS increased cortico-striatal evoked responses in healthy, but not in dystonic tissue. b. Commensurate with this, DBS increased inhibitory control of these evoked responses in dystonic, and decreased inhibitory control in healthy tissue. c. Further, DBS reduced mEPSC frequency strongly in dystonic, and less prominently in healthy tissue, showing that also a modulation of presynaptic mechanisms is likely involved. d. Cellular properties of medium-spiny neurones remained unchanged. We conclude that DBS leads to dampening of cortico-striatal communication, and restores intrastriatal inhibitory tone.

Pentylenetetrazol kindling induces cortical astrocytosis and increased expression of extracellular matrix molecules in mice

Although epilepsy is one of the most common chronic neurological disorders with a prevalence of approximately 1.0 %, the underlying pathophysiology remains to be elucidated. Understanding the molecular and cellular mechanisms involved in the development of epilepsy is important for the development of appropriate therapeutic strategy. In this study, we investigated the effects of status epilepticus on astrocytes, microglia, and extracellular matrix (ECM) molecules in the somatosensory cortex and piriform cortex of mice. Activation of astrocytes was observed in many cortices except the retrosplenial granular cortex after pentylenetetrazol (PTZ)-induced kindling in mice. Activated astrocytes in the cortex were found in layers 1-3 but not in layers 4-6. In the somatosensory and piriform cortices, no change was observed in the number of parvalbumin (PV)-positive neurons and PV-positive neurons covered with perineuronal nets. However, the amount of ECM in the extracellular space increased. The expression of VGLUT1- and GAD67-positive synapses also increased. Thus, in the PTZ-kindling epilepsy mice model, an increase in the number of ECM molecules and activation of astrocytes were observed in the somatosensory cortex and piriform cortex. These results indicate that PTZ-induced seizures affect not only the hippocampus but also other cortical areas. Our study findings may help to develop new therapeutic approaches to prevent seizures or their sequelae.

Anticonvulsant effects after grafting of rat, porcine, and human mesencephalic neural progenitor cells into the rat subthalamic nucleus

Cell transplantation based therapy is a promising strategy for treating intractable epilepsies. Inhibition of the subthalamic nucleus (STN) or substantia nigra pars reticulata (SNr) is a powerful experimental approach for remote control of different partial seizure types, when targeting the seizure focus is not amenable. Here, we tested the hypothesis that grafting of embryonic/fetal neural precursor cells (NPCs) from various species (rat, human, pig) into STN or SNr of adult rats induces anticonvulsant effects. To rationally refine this approach, we included NPCs derived from the medial ganglionic eminence (MGE) and ventral mesencephalon (VM), both of which are able to develop a GABAergic phenotype. All VM- and MGE-derived cells showed intense migration behavior after grafting into adult rats, developed characteristics of inhibitory interneurons, and survived at least up to 4 months after transplantation. By using the intravenous pentylenetetrazole (PTZ) seizure threshold test in adult rats, transient anticonvulsant effects were observed after bilateral grafting of NPCs derived from human and porcine VM into STN, but not after SNr injection (site-specificity). In contrast, MGE-derived NPCs did not cause anticonvulsant effects after grafting into STN or SNr (cell-specificity). Neither induction of status epilepticus by lithium-pilocarpine to induce neuronal damage prior to the PTZ test nor pretreatment of MGE cells with retinoic acid and potassium chloride to increase differentiation into GABAergic neurons could enhance anticonvulsant effectiveness of MGE cells. This is the first proof-of-principle study showing anticonvulsant effects by bilateral xenotransplantation of NPCs into the STN. Our study highlights the value of VM-derived NPCs for interneuron-based cell grafting targeting the STN.

Stable Knockdown of Adenosine Kinase by Lentiviral Anti-ADK miR-shRNAs in Wharton's Jelly Stem Cells

Objective

In this study, we describe an efficient approach for stable knockdown of adenosine kinase (ADK) using lentiviral system, in an astrocytoma cell line and in human Wharton’s jelly mesenchymal stem cells (hWJMSCs). These sources of stem cells besides having multilineage differentiation potential and immunomodulatory activities, are easily available in unlimited numbers, do not raise ethical concerns and are attractive for gene manipulation and cell-based gene therapy.

Materials and Methods

In this experimental study, we targeted adenosine kinase mRNA at 3' and performed coding sequences using eight miR-based expressing cassettes of anti-ADK short hairpin RNA (shRNAs). First, these cassettes with scrambled control sequences were cloned into expressing lentiviral pGIPZ vector. Quantitative real time-polymerase chain reaction (qRT-PCR) was used to screen multi-cassettes anti-ADK miR-shRNAs in stably transduced U-251 MG cell line and measuring ADK gene expression at mRNA level. Extracted WJMSCs were characterized using flow cytometry for expressing mesenchymal specific marker (CD44+) and lack of expression of hematopoietic lineage marker (CD45-). Then, the lentiviral vector that expressed the most efficient anti-ADK miR-shRNA, was employed to stably transduce WJMSCs.

Results

Transfection of anti-ADK miR-shRNAs in HEK293T cells using CaPO₄ method showed high efficiency. We successfully transduced U-251 cell line by recombinant lentiviruses and screened eight cassettes of anti-ADK miR- shRNAs in stably transduced U-251 MG cell line by qRT-PCR. RNAi-mediated down-regulation of ADK by lentiviral system indicated up to 95% down-regulation of ADK. Following lentiviral transduction of WJMSCs with anti-ADK miR- shRNA expression cassette, we also implicated, down-regulation of ADK up to 95% by qRT-PCR and confirmed it by western blot analysis at the protein level.

Conclusion

Our findings indicate efficient usage of shRNA cassette for ADK knockdown. Engineered WJMSCs with genome editing methods like CRISPR/cas9 or more safe viral systems such as adeno-associated vectors (AAV) might be an attractive source in cell-based gene therapy and may have therapeutic potential for epilepsy.

Hippocampal GABAergic Inhibitory Interneurons

In the hippocampus GABAergic local circuit inhibitory interneurons represent only ~10-15% of the total neuronal population; however, their remarkable anatomical and physiological diversity allows them to regulate virtually all aspects of cellular and circuit function. Here we provide an overview of the current state of the field of interneuron research, focusing largely on the hippocampus. We discuss recent advances related to the various cell types, including their development and maturation, expression of subtype-specific voltage- and ligand-gated channels, and their roles in network oscillations. We also discuss recent technological advances and approaches that have permitted high-resolution, subtype-specific examination of their roles in numerous neural circuit disorders and the emerging therapeutic strategies to ameliorate such pathophysiological conditions. The ultimate goal of this review is not only to provide a touchstone for the current state of the field, but to help pave the way for future research by highlighting where gaps in our knowledge exist and how a complete appreciation of their roles will aid in future therapeutic strategies.

Neural Stem Cell or Human Induced Pluripotent Stem Cell-Derived GABA-ergic Progenitor Cell Grafting in an Animal Model of Chronic Temporal Lobe Epilepsy

Grafting of neural stem cells (NSCs) or GABA-ergic progenitor cells (GPCs) into the hippocampus could offer an alternative therapy to hippocampal resection in patients with drug-resistant chronic epilepsy, which afflicts >30% of temporal lobe epilepsy (TLE) cases. Multipotent, self-renewing NSCs could be expanded from multiple regions of the developing and adult brain, human embryonic stem cells (hESCs), and human induced pluripotent stem cells (hiPSCs). On the other hand, GPCs could be generated from the medial and lateral ganglionic eminences of the embryonic brain and from hESCs and hiPSCs. To provide comprehensive methodologies involved in testing the efficacy of transplantation of NSCs and GPCs in a rat model of chronic TLE, NSCs derived from the rat medial ganglionic eminence (MGE) and MGE-like GPCs derived from hiPSCs are taken as examples in this unit. The topics comprise description of the required materials, reagents and equipment, methods for obtaining rat MGE-NSCs and hiPSC-derived MGE-like GPCs in culture, generation of chronically epileptic rats, intrahippocampal grafting procedure, post-grafting evaluation of the effects of grafts on spontaneous recurrent seizures and cognitive and mood impairments, analyses of the yield and the fate of graft-derived cells, and the effects of grafts on the host hippocampus. © 2016 by John Wiley & Sons, Inc.

GABA-ergic cell therapy for epilepsy: Advances, limitations and challenges

Diminution in the number of gamma-amino butyric acid positive (GABA-ergic) interneurons and their axon terminals, and/or alterations in functional inhibition are conspicuous brain alterations believed to contribute to the persistence of seizures in acquired epilepsies such as temporal lobe epilepsy. This has steered a perception that replacement of lost GABA-ergic interneurons would improve inhibitory synaptic neurotransmission in the epileptic brain region and thereby reduce the occurrence of seizures. Indeed, studies using animal prototypes have reported that grafting of GABA-ergic progenitors derived from multiple sources into epileptic regions can reduce seizures. This review deliberates recent advances, limitations and challenges concerning the development of GABA-ergic cell therapy for epilepsy. The efficacy and limitations of grafts of primary GABA-ergic progenitors from the embryonic lateral ganglionic eminence and medial ganglionic eminence (MGE), neural stem/progenitor cells expanded from MGE, and MGE-like progenitors generated from human pluripotent stem cells for alleviating seizures and co-morbidities of epilepsy are conferred. Additional studies required for possible clinical application of GABA-ergic cell therapy for epilepsy are also summarized.

Interneuron Transplantation as a Treatment for Epilepsy

Stem-cell therapy has extraordinary potential to address critical, unmet needs in the treatment of human disease. One particularly promising approach for the treatment of epilepsy is to increase inhibition in areas of the epileptic brain by grafting new inhibitory cortical interneurons. When grafted from embryos, young γ-aminobutyric acid (GABA)ergic precursors disperse, functionally mature into host brain circuits as local-circuit interneurons, and can stop seizures in both genetic and acquired forms of the disease. These features make interneuron cell transplantation an attractive new approach for the treatment of intractable epilepsies, as well as other brain disorders that involve increased risk for epilepsy as a comorbidity. Here, we review recent efforts to isolate and transplant cortical interneuron precursors derived from embryonic mouse and human cell sources. We also discuss some of the important challenges that must be addressed before stem-cell-based treatment for human epilepsy is realized.

Long-term seizure suppression and optogenetic analyses of synaptic connectivity in epileptic mice with hippocampal grafts of GABAergic interneurons

Studies in rodent epilepsy models suggest that GABAergic interneuron progenitor grafts can reduce hyperexcitability and seizures in temporal lobe epilepsy (TLE). Although integration of the transplanted cells has been proposed as the underlying mechanism for these disease-modifying effects, prior studies have not explicitly examined cell types and synaptic mechanisms for long-term seizure suppression. To address this gap, we transplanted medial ganglionic eminence (MGE) cells from embryonic day 13.5 VGAT-Venus or VGAT-ChR2-EYFP transgenic embryos into the dentate gyrus (DG) of adult mice 2 weeks after induction of TLE with pilocarpine. Beginning 3-4 weeks after status epilepticus, we conducted continuous video-electroencephalographic recording until 90-100 d. TLE mice with bilateral MGE cell grafts in the DG had significantly fewer and milder electrographic seizures, compared with TLE controls. Immunohistochemical studies showed that the transplants contained multiple neuropeptide or calcium-binding protein-expressing interneuron types and these cells established dense terminal arborizations onto the somas, apical dendrites, and axon initial segments of dentate granule cells (GCs). A majority of the synaptic terminals formed by the transplanted cells were apposed to large postsynaptic clusters of gephyrin, indicative of mature inhibitory synaptic complexes. Functionality of these new inhibitory synapses was demonstrated by optogenetically activating VGAT-ChR2-EYFP-expressing transplanted neurons, which generated robust hyperpolarizations in GCs. These findings suggest that fetal GABAergic interneuron grafts may suppress pharmacoresistant seizures by enhancing synaptic inhibition in DG neural circuits.

Human fetal brain-derived neural stem/progenitor cells grafted into the adult epileptic brain restrain seizures in rat models of temporal lobe epilepsy

Cell transplantation has been suggested as an alternative therapy for temporal lobe epilepsy (TLE) because this can suppress spontaneous recurrent seizures in animal models. To evaluate the therapeutic potential of human neural stem/progenitor cells (huNSPCs) for treating TLE, we transplanted huNSPCs, derived from an aborted fetal telencephalon at 13 weeks of gestation and expanded in culture as neurospheres over a long time period, into the epileptic hippocampus of fully kindled and pilocarpine-treated adult rats exhibiting TLE. In vitro, huNSPCs not only produced all three central nervous system neural cell types, but also differentiated into ganglionic eminences-derived γ-aminobutyric acid (GABA)-ergic interneurons and released GABA in response to the depolarization induced by a high K⁺ medium. NSPC grafting reduced behavioral seizure duration, afterdischarge duration on electroencephalograms, and seizure stage in the kindling model, as well as the frequency and the duration of spontaneous recurrent motor seizures in pilocarpine-induced animals. However, NSPC grafting neither improved spatial learning or memory function in pilocarpine-treated animals. Following transplantation, grafted cells showed extensive migration around the injection site, robust engraftment, and long-term survival, along with differentiation into β-tubulin III⁺ neurons (∼34%), APC-CC1⁺ oligodendrocytes (∼28%), and GFAP⁺ astrocytes (∼8%). Furthermore, among donor-derived cells, ∼24% produced GABA. Additionally, to explain the effect of seizure suppression after NSPC grafting, we examined the anticonvulsant glial cell-derived neurotrophic factor (GDNF) levels in host hippocampal astrocytes and mossy fiber sprouting into the supragranular layer of the dentate gyrus in the epileptic brain. Grafted cells restored the expression of GDNF in host astrocytes but did not reverse the mossy fiber sprouting, eliminating the latter as potential mechanism. These results suggest that human fetal brain-derived NSPCs possess some therapeutic effect for TLE treatments although further studies to both increase the yield of NSPC grafts-derived functionally integrated GABAergic neurons and improve cognitive deficits are still needed.

Anticonvulsant Effects by Bilateral and Unilateral Transplantation of GABA-Producing Cells into the Subthalamic Nucleus in an Acute Seizure Model

Neural transplantation of GABA-producing cells into key structures within seizure-suppressing circuits holds promise for medication-resistant epilepsy patients not eligible for resection of the epileptic focus. The substantia nigra pars reticulata (SNr), a basal ganglia output structure, is well known to modulate different seizure types. A recent microinjection study by our group indicated that the subthalamic nucleus (STN), which critically regulates nigral activity, might be a more promising target for focal therapy in epilepsies than the SNr. As a proof of principle, we therefore assessed the anticonvulsant efficacy of bilateral and unilateral allografting of GABA-producing cell lines into the STN using the timed intravenous pentylenetetrazole seizure threshold test, which allows repeated seizure threshold determinations in individual rats. We observed (a) that grafted cells survived up to the end of the experiments, (b) that anticonvulsant effects can be induced by bilateral transplantation into the STN using immortalized GABAergic cells derived from the rat embryonic striatum and cells additionally transfected to obtain higher GABA synthesis than the parent cell line, and (c) that anticonvulsant effects were observed even after unilateral transplantation into the STN. Neither grafting of control cells nor transplantation outside the STN induced anticonvulsant effects, emphasizing the site and cell specificity of the observed anticonvulsant effects. To our knowledge, the present study is the first showing anticonvulsant effects by grafting of GABA-producing cells into the STN. The STN can be considered a highly promising target region for modulation of seizure circuits and, moreover, has the advantage of being clinically established for functional neurosurgery.

Cortical interneurons from human pluripotent stem cells: prospects for neurological and psychiatric disease

Cortical interneurons represent 20% of the cells in the cortex. These cells are local inhibitory neurons whose function is to modulate the firing activities of the excitatory projection neurons. Cortical interneuron dysfunction is believed to lead to runaway excitation underlying (or implicated in) seizure-based diseases, such as epilepsy, autism, and schizophrenia. The complex development of this cell type and the intricacies involved in defining the relative subtypes are being increasingly well defined. This has led to exciting experimental cell therapy in model organisms, whereby fetal-derived interneuron precursors can reverse seizure severity and reduce mortality in adult epileptic rodents. These proof-of-principle studies raise hope for potential interneuron-based transplantation therapies for treating epilepsy. On the other hand, cortical neurons generated from patient iPSCs serve as a valuable tool to explore genetic influences of interneuron development and function. This is a fundamental step in enhancing our understanding of the molecular basis of neuropsychiatric illnesses and the development of targeted treatments. Protocols are currently being developed for inducing cortical interneuron subtypes from mouse and human pluripotent stem cells. This review sets out to summarize the progress made in cortical interneuron development, fetal tissue transplantation and the recent advance in stem cell differentiation toward interneurons.

Neural stem cell grafting in an animal model of chronic temporal lobe epilepsy

Neural stem cell (NSC) transplantation into the hippocampus could offer an alternative therapy to hippocampal resection in patients with drug-resistant chronic epilepsy, which afflicts ∼30% of mesial temporal lobe epilepsy (TLE) cases. Multipotent, self-renewing NSCs could be expanded from multiple regions of the developing and adult brain, human embryonic stem cells (hESCs), and induced pluripotent stem cells (iPSCs). However, to provide a comprehensive methodology involved in testing the efficacy of transplantation of NSCs in a rat model of chronic TLE, NSCs derived from the embryonic medial ganglionic eminence (MGE) are taken as an example in this unit. The topics comprise description of the required materials, reagents and equipment, and protocols for expanding MGE-NSCs in culture, generating chronically epileptic rats, the intrahippocampal grafting, post-grafting evaluation of the effects of NSC grafts on spontaneous recurrent seizures and cognitive impairments, analyses of the yield and the fate of graft-derived cells, and the effects of NSC grafts on the host hippocampus.

The promise of an interneuron-based cell therapy for epilepsy

Of the nearly 3 million Americans diagnosed with epilepsy, approximately 30% are unresponsive to current medications. Recent data has shown that early postnatal transplantation of interneuronal precursor cells increases GABAergic inhibition in the host brain and dramatically suppresses seizure activity in epileptic mice. In this review, we will highlight findings from seizure-prone mice and humans that demonstrate the link between dysfunctional GABAergic inhibition and hyperexcitability. In particular, we will focus on rodent models of temporal lobe epilepsy, the most common and difficult to treat form of the disease, and interneuronopathies, an emerging classification. A wealth of literature showing a causal link between reduced GABA-mediated inhibition and seizures has directed our efforts to recover the loss of inhibition via transplantation of interneuronal precursors. Numerous related studies have explored the anticonvulsant potential of cell grafts derived from a variety of brain regions, yet the mechanism underlying the effect of such heterogeneous cell transplants is unknown. In discussing our recent findings and placing them in context with what is known about epilepsy, and how related transplant approaches have progressed, we hope to initiate a frank discussion of the best path toward the translation of this approach to patients with intractable forms of epilepsy.

CALIBRATION OF NEUROTRANSMITTER RELEASE FROM NEURAL CELLS FOR THERAPEUTIC IMPLANTS

In this work we quantified the in vitro calibration relationships between high frequency electrical stimulation and GABA and glutamate release in both mature retinoic acid differentiated P19 neurons and immortalized embryonic cortical cells engineered to express glutamic acid decarboxylase, GAD65. Extracellular glutamate and GABA was quantified by 2D gas chromatography and time of flight mass spectrometry after stimulation at varying amplitudes and frequencies. Amplitude sweeps resulted in a linear calibration for P19 neurons; the level of neurotransmitter varied over one order of magnitude from ~ 200 pg/neuron to ~ 1.2 ng/neuron for glutamate and ~ 1 ng/neuron to ~ 2 ng/neuron for GABA, depending on the stimulation amplitude. Frequency sweeps resulted in a peak release at 250 Hz for glutamate and 400 Hz for GABA in P19 cells. The GABA transporter inhibitor, nipecotic acid, increased extracellular GABA levels and decrease glutamate. In contrast the embryonic cortical cells had a strongly nonlinear dependency of release on stimulation amplitude, and a weak dependence on frequency. These cells had roughly equal extracellular glutamate and GABA levels after stimulation despite the expression of GAD65. In addition glutamate and GABA levels were insensitive to nipecotic acid. These results demonstrate an ability to calibrate and tune neurotransmitter release from neural cells using high frequency stimulation parameters.

Current prospects and challenges for epilepsy gene therapy

This review addresses the state of gene therapy research for the treatment of epilepsy. Preclinical studies have demonstrated the anti-seizure efficacy of viral vector-based gene transfer through the use of a variety of strategies - from modulating classic neurotransmitter systems to targeting or overexpressing of neuropeptide receptors in seizure-specific brain regions. While these studies provide substantive proof of principle for viral vector gene therapy, future studies must address the challenges of vector immunity, cellular specificity and effective global delivery. As these issues are resolved, viral vector gene therapy should significantly impact the treatment of intractable epilepsy.

Progress in cell grafting therapy for temporal lobe epilepsy

Temporal lobe epilepsy (TLE), exemplified by complex partial seizures, is recognized in ~30% of epileptic patients. Seizures in TLE are associated with cognitive dysfunction and are resistant to antiepileptic drug therapy in ~35% of patients. Although surgical resection of the hippocampus bestows improved seizure regulation in most cases of intractable TLE, this choice can cause lasting cognitive deficiency and reliance on antiepileptic drugs. Thus, alternative therapies that are proficient in both containing the spontaneous recurrent seizures and reversing the cognitive dysfunction are needed. The cell transplantation approach is promising in serving as an adept alternate therapy for TLE, because this strategy has shown the capability to curtail epileptogenesis when used soon after an initial precipitating brain injury, and to restrain spontaneous recurrent seizures and improve cognitive function when utilized after the occurrence of TLE. Nonetheless, this treatment needs further advancement and rigorous evaluation in animal prototypes of chronic TLE before the conceivable clinical use. It is especially vital to gauge the efficacy of distinct donor cell types, such as the hippocampal precursor cells, γ-aminobutyric acid-ergic progenitors, and neural stem cells derived from diverse human sources (including the embryonic stem cells and induced pluripotent stem cells) for longstanding seizure suppression using continuous electroencephalographic recordings for prolonged periods. Additionally, the identification of the mechanisms underlying the graft-mediated seizure suppression and improved cognitive function, and the development of apt grafting strategies that enhance the anti-seizure and pro-cognitive effects of grafts will be necessary. The goal of this review is to evaluate the progress made hitherto in this area and to discuss the prospect for cell-based therapy for TLE.

Promise of resveratrol for easing status epilepticus and epilepsy

Resveratrol (RESV; 3,5,4'-tri-hydroxy stilbene), a naturally occurring phytoalexin, is found at a high concentration in the skin of red grapes and red wine. RESV mediates a wide-range of biological activities, which comprise an increased life span, anti-ischemic, anti-cancer, antiviral, anti-aging and anti-inflammatory properties. Studies in several animal prototypes of brain injury suggest that RESV is an effective neuroprotective compound. Ability to enter the brain after a peripheral administration and no adverse effects on the brain or body are other features that are appealing for using this compound as a therapy for brain injury or neurodegenerative diseases. The goal of this review is to discuss the promise of RESV for treating acute seizures, preventing the acute seizure or status epilepticus induced development of chronic epilepsy, and easing the chronic epilepsy typified by spontaneous recurrent seizures and cognitive dysfunction. First, the various beneficial effects of RESV on the normal brain are discussed to provide a rationale for considering RESV treatment in the management of acute seizures and epilepsy. Next, the detrimental effects of acute seizures or status epilepticus on the hippocampus and the implications of post-status epilepticus changes in the hippocampus towards the occurrence of chronic epilepsy and cognitive dysfunction are summarized. The final segment evaluates studies that have used RESV as a neuroprotective compound against seizures, and proposes studies that are critically needed prior to the clinical application of RESV as a prophylaxis against the development of chronic epilepsy and cognitive dysfunction after an episode of status epilepticus or head injury.

Neuromodulation in Epilepsy

Neuromodulation strategies have been proposed to treat a variety of neurological disorders, including medication-resistant epilepsy. Electrical stimulation of both central and peripheral nervous systems has emerged as a possible alternative for patients who are not deemed to be good candidates for resective procedures. In addition to well-established treatments such as vagus nerve stimulation, epilepsy centers around the world are investigating the safety and efficacy of neurostimulation at different brain targets, including the hippocampus, thalamus, and subthalamic nucleus. Also promising are the preliminary results of responsive neuromodulation studies, which involve the delivery of stimulation to the brain in response to detected epileptiform or preepileptiform activity. In addition to electrical stimulation, novel therapeutic methods that may open new horizons in the management of epilepsy include transcranial magnetic stimulation, focal drug delivery, cellular transplantation, and gene therapy. We review the current strategies and future applications of neuromodulation in epilepsy.

Bone marrow mononuclear cells reduce seizure frequency and improve cognitive outcome in chronic epileptic rats

AIMS

Epilepsy affects 0.5-1% of the world's population, and approximately a third of these patients are refractory to current medication. Given their ability to proliferate, differentiate and regenerate tissues, stem cells could restore neural circuits lost during the course of the disease and reestablish the physiological excitability of neurons. This study verified the therapeutic potential of bone marrow mononuclear cells (BMMCs) on seizure control and cognitive impairment caused by experimentally induced epilepsy.

MAIN METHODS

Status epilepticus (SE) was induced by lithium-pilocarpine injection and controlled with diazepam 90 min after SE onset. Lithium-pilocarpine-treated rats were intravenously transplanted 22 days after SE with BMMCs obtained from enhanced green fluorescent protein (eGFP) transgenic C57BL/6 mice. Control epileptic animals were given an equivalent volume of saline or fibroblast injections. Animals were video-monitored for the presence of spontaneous recurrent seizures prior to and following the cell administration procedure. In addition, rats underwent cognitive evaluation using a Morris water maze.

KEY FINDINGS

Our data show that BMMCs reduced the frequency of seizures and improved the learning and long-term spatial memory impairments of epileptic rats. EGFP-positive cells were detected in the brains of transplanted animals by PCR analysis.

SIGNIFICANCE

The positive behavioral effects observed in our study indicate that BMMCs could represent a promising therapeutic option in the management of chronic temporal lobe epilepsy.

GABAergic neuronal precursor grafting: implications in brain regeneration and plasticity

Numerous neurological disorders are caused by a dysfunction of the GABAergic system that impairs or either stimulates its inhibitory action over its neuronal targets. Pharmacological drugs have generally been proved very effective in restoring its normal function, but their lack of any sort of spatial or cell type specificity has created some limitations in their use. In the last decades, cell-based therapies using GABAergic neuronal grafts have emerged as a promising treatment, since they may restore the lost equilibrium by cellular replacement of the missing/altered inhibitory neurons or modulating the hyperactive excitatory system. In particular, the discovery that embryonic ganglionic eminence-derived GABAergic precursors are able to disperse and integrate in large areas of the host tissue after grafting has provided a strong rationale for exploiting their use for the treatment of diseased brains. GABAergic neuronal transplantation not only is efficacious to restore normal GABAergic activities but can also trigger or sustain high neuronal plasticity by promoting the general reorganization of local neuronal circuits adding new synaptic connections. These results cast new light on dynamics and plasticity of adult neuronal assemblies and their associated functions disclosing new therapeutic opportunities for the near future.

Medial ganglionic eminence-derived neural stem cell grafts ease spontaneous seizures and restore GDNF expression in a rat model of chronic temporal lobe epilepsy

Nearly 30% of patients with mesial temporal lobe epilepsy (TLE) are resistant to treatment with antiepileptic drugs. Neural stem cell (NSC) grafting into the hippocampus could offer an alternative therapy to hippocampal resection in these patients. As TLE is associated with reduced numbers of inhibitory gamma-amino butyric acid (GABA)-ergic interneurons and astrocytes expressing the anticonvulsant glial-derived neurotrophic factor (GDNF) in the hippocampus, we tested the hypothesis that grafting of NSCs that are capable of adding new GABA-ergic interneurons and GDNF-expressing astrocytes into the epileptic hippocampus restrains spontaneous recurrent motor seizures (SRMS) in chronic TLE. We grafted NSCs expanded in vitro from embryonic medial ganglionic eminence (MGE) into hippocampi of adult rats exhibiting chronic TLE with cognitive impairments. NSC grafting reduced frequencies of SRMS by 43% and stage V seizures by 90%. The duration of individual SRMS and the total time spent in seizures were reduced by 51 and 74%, respectively. Grafting did not improve the cognitive function however. Graft-derived cells (equivalent to approximately 28% of injected cells) were observed in various layers of the epileptic hippocampus where they differentiated into NeuN+ neurons (13%), S-100beta+ astrocytes (57%), and NG2+ oligodendrocyte-progenitors (3%). Furthermore, among graft-derived cells, 10% expressed GABA and 50% expressed GDNF. Additionally, NSC grafting restored GDNF in a vast majority of the hippocampal astrocytes but had no effect on neurogenesis. Thus, MGE-NSC therapy is efficacious for diminishing SRMS in chronic TLE. Addition of new GABA-ergic neurons and GDNF+ cells, and restoration of GDNF in the hippocampal astrocytes may underlie the therapeutic effect of MGE-NSC grafts.

Injection of embryonic median ganglionic eminence cells or fibroblasts within the amygdala in rats kindled from the piriform cortex

BACKGROUND

Intracerebral infusion of anticonvulsant agent secreting cells has proven to raise the threshold for seizure generation in epileptogenic areas. Median ganglionic eminence (MGE) is the main embryonic region where future GABAergic cells originate. Here we report the results of intraamygdaline grafting of MGE cells versus fibroblasts in a piriform cortex kindling model of epilepsy in the rat.

MATERIAL AND METHODS

Rats were implanted with an electrode in the left piriform cortex and subjected to infusion at the left basolateral amygdala of cells obtained from the MGE of embryos or fibroblasts. Some of the donor cells were obtained from transgenic rats expressing the green fluorescent protein (GFP). Seizure and neurologic behavior were recorded, and inmunohistochemical and ultrastructural studies were carried out.

RESULTS

Cells obtained from the embryonic MGE elevated both the afterdischarge and the seizure threshold progressively, being significant 3 weeks after their injection. On the contrary, fibroblasts injected into the amygdala raised the seizure thresholds the first week, the effect weaning during the following weeks. Fibroblasts and MGE cells were shown at the injected amygdala. No behavioral side effects were recorded in either experimental group.

CONCLUSION

MGE cells implanted at the amygdala may control the focal component of temporolimbic seizures. This effect may be mediated by local release of GABA.

Vulnerability of hippocampal GABA-ergic interneurons to kainate-induced excitotoxic injury during old age

Hippocampal inhibitory interneurons expressing glutamate decarboxylase-67 (GAD-67) considerably decline in number during old age. Studies in young adult animals further suggest that hippocampal GAD-67+ interneuron population is highly vulnerable to excitotoxic injury. However, the relative susceptibility of residual GAD-67+ interneurons in the aged hippocampus to excitotoxic injury is unknown. To elucidate this, using both adult and aged F344 rats, we performed stereological counting of GAD-67+ interneurons in different layers of the dentate gyrus and CA1 & CA3 sub-fields, at 3 months post-excitotoxic hippocampal injury inflicted through an intracerebroventricular administration of kainic acid (KA). Substantial reductions of GAD-67+ interneurons were found in all hippocampal layers and sub-fields after KA-induced injury in adult animals. Contrastingly, there was no significant change in GAD-67+ interneuron population in any of the hippocampal layers and sub-fields following similar injury in aged animals. Furthermore, the stability of GAD-67+ interneurons in aged rats after KA was not attributable to milder injury, as the overall extent of KA-induced hippocampal principal neuron loss was comparable between adult and aged rats. Interestingly, because of the age-related disparity in vulnerability of interneurons to injury, the surviving GAD-67+ interneuron population in the injured aged hippocampus remained comparable to that observed in the injured adult hippocampus despite enduring significant reductions in interneuron number with aging. Thus, unlike in the adult hippocampus, an excitotoxic injury to the aged hippocampus does not result in significantly decreased numbers of GAD-67+ interneurons. Persistence of GAD-67+ interneuron population in the injured aged hippocampus likely reflects an age-related change in the response of GAD-67+ interneurons to excitotoxic hippocampal injury. These results have implications towards understanding mechanisms underlying the evolution of initial precipitating injury into temporal lobe epilepsy in the elderly population.

Vulnerability of hippocampal GABA-ergic interneurons to kainate-induced excitotoxic injury during old age

Hippocampal inhibitory interneurons expressing glutamate decarboxylase-67 (GAD-67) considerably decline in number during old age. Studies in young adult animals further suggest that hippocampal GAD-67+ interneuron population is highly vulnerable to excitotoxic injury. However, the relative susceptibility of residual GAD-67+ interneurons in the aged hippocampus to excitotoxic injury is unknown. To elucidate this, using both adult and aged F344 rats, we performed stereological counting of GAD-67+ interneurons in different layers of the dentate gyrus and CA1 & CA3 sub-fields, at 3 months post-excitotoxic hippocampal injury inflicted through an intracerebroventricular administration of kainic acid (KA). Substantial reductions of GAD-67+ interneurons were found in all hippocampal layers and sub-fields after KA-induced injury in adult animals. Contrastingly, there was no significant change in GAD-67+ interneuron population in any of the hippocampal layers and sub-fields following similar injury in aged animals. Furthermore, the stability of GAD-67+ interneurons in aged rats after KA was not attributable to milder injury, as the overall extent of KA-induced hippocampal principal neuron loss was comparable between adult and aged rats. Interestingly, because of the age-related disparity in vulnerability of interneurons to injury, the surviving GAD-67+ interneuron population in the injured aged hippocampus remained comparable to that observed in the injured adult hippocampus despite enduring significant reductions in interneuron number with aging. Thus, unlike in the adult hippocampus, an excitotoxic injury to the aged hippocampus does not result in significantly decreased numbers of GAD-67+ interneurons. Persistence of GAD-67+ interneuron population in the injured aged hippocampus likely reflects an age-related change in the response of GAD-67+ interneurons to excitotoxic hippocampal injury. These results have implications towards understanding mechanisms underlying the evolution of initial precipitating injury into temporal lobe epilepsy in the elderly population.

Cell and gene therapies for refractory epilepsy

Despite recent advances in the development of antiepileptic drugs, refractory epilepsy remains a major clinical problem affecting up to 35% of patients with partial epilepsy. Currently, there are few therapies that affect the underlying disease process. Therefore, novel therapeutic concepts are urgently needed. The recent development of experimental cell and gene therapies may offer several advantages compared to conventional systemic pharmacotherapy: (i) Specificity to underlying pathogenetic mechanisms by rational design; (ii) specificity to epileptogenic networks by focal delivery; and (iii) avoidance of side effects. A number of naturally occurring brain substances, such as GABA, adenosine, and the neuropeptides galanin and neuropeptide Y, may function as endogenous anticonvulsants and, in addition, may interact with the process of epileptogenesis. Unfortunately, the systemic application of these compounds is compromised by limited bioavailability, poor penetration of the blood-brain barrier, or the widespread systemic distribution of their respective receptors. Therefore, in recent years a new field of cell and gene-based neuropharmacology has emerged, aimed at either delivering endogenous anticonvulsant compounds by focal intracerebral transplantation of bioengineered cells (ex vivo gene therapy), or by inducing epileptogenic brain areas to produce these compounds in situ (in vivo gene therapy). In this review, recent efforts to develop GABA-, adenosine-, galanin-, and neuropeptide Y- based cell and gene therapies are discussed. The neurochemical rationales for using these compounds are discussed, the advantages of focal applications are highlighted and preclinical cell transplantation and gene therapy studies are critically evaluated. Although many promising data have been generated recently, potential problems, such as long-term therapeutic efficacy, long-term safety, and efficacy in clinically relevant animal models, need to be addressed before clinical applications can be contemplated.

Recent advancements in stem cell and gene therapies for neurological disorders and intractable epilepsy

The potential applications of stem cell therapies for treating neurological disorders are enormous. Many laboratories are focusing on stem cell treatments for CNS diseases, including spinal cord injury, Amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, multiple sclerosis, stroke, traumatic brain injury, and epilepsy. Among the many stem cell types under testing for neurological treatments, the most common are fetal and adult brain stem cells, embryonic stem cells, induced pluripotent stem cells, and mesenchymal stem cells. An expanding toolbox of molecular probes is now available to allow analyses of neural stem cell fates prior to and after transplantation. Concomitantly, protocols are being developed to direct the fates of stem cell-derived neural progenitors, and also to screen stem cells for tumorigenicity and aneuploidy. The rapid progress in the field suggests that novel stem cell and gene therapies for neurological disorders are in the pipeline.

Advances in the application of technology to epilepsy: the CIMIT/NIO Epilepsy Innovation Summit

In 2008, a group of clinicians, scientists, engineers, and industry representatives met to discuss advances in the application of engineering technologies to the diagnosis and treatment of patients with epilepsy. The presentations also provided a guide for further technological development, specifically in the evaluation of patients for epilepsy surgery, seizure onset detection and seizure prediction, intracranial treatment systems, and extracranial treatment systems. This article summarizes the discussions and demonstrates that cross-disciplinary interactions can catalyze collaborations between physicians and engineers to address and solve many of the pressing unmet needs in epilepsy.

Reduction of seizures by transplantation of cortical GABAergic interneuron precursors into Kv1.1 mutant mice

Epilepsy, a disease characterized by abnormal brain activity, is a disabling and potentially life-threatening condition for nearly 1% of the world population. Unfortunately, modulation of brain excitability using available antiepileptic drugs can have serious side effects, especially in the developing brain, and some patients can only be improved by surgical removal of brain regions containing the seizure focus. Here, we show that bilateral transplantation of precursor cells from the embryonic medial ganglionic eminence (MGE) into early postnatal neocortex generates mature GABAergic interneurons in the host brain. In mice receiving MGE cell grafts, GABA-mediated synaptic and extrasynaptic inhibition onto host brain pyramidal neurons is significantly increased. Bilateral MGE cell grafts in epileptic mice lacking a Shaker-like potassium channel (a gene mutated in one form of human epilepsy) resulted in significant reductions in the duration and frequency of spontaneous electrographic seizures. Our findings suggest that MGE-derived interneurons could be used to ameliorate abnormal excitability and possibly act as an effective strategy in the treatment of epilepsy.

Combined extrinsic and intrinsic manipulations exert complementary neuronal enrichment in embryonic rat neural precursor cultures: an in vitro and in vivo analysis

Numerous central nervous system (CNS) disorders share a common pathology in dysregulation of gamma-aminobutyric acid (GABA) inhibitory signaling. Transplantation of GABA-releasing cells at the site of disinhibition holds promise for alleviating disease symptoms with fewer side effects than traditional drug therapies. We manipulated fibroblast growth factor (FGF)-2 deprivation and mammalian achaete-scute homolog (MASH)1 transcription factor levels in an attempt to amplify the default GABAergic neuronal fate in cultured rat embryonic neural precursor cells (NPCs) for use in transplantation studies. Naïve and MASH1 lentivirus-transduced NPCs were maintained in FGF-2 or deprived of FGF-2 for varying lengths of time. Immunostaining and quantitative analysis showed that GABA- and beta-III-tubulin-immunoreactive cells generally decreased through successive passages, suggesting a loss of neurogenic potential in rat neurospheres expanded in vitro. However, FGF-2 deprivation resulted in a small, but significantly increased population of GABAergic cells derived from passaged neurospheres. In contrast to naïve and GFP lentivirus-transduced clones, MASH1 transduction resulted in increased bromodeoxyuridine (BrdU) incorporation and clonal colony size. Western blotting showed that MASH1 overexpression and FGF-2 deprivation additively increased beta-III-tubulin and decreased cyclic nucleotide phosphodiesterase (CNPase) expression, whereas FGF-2 deprivation alone attenuated glial fibrillary acidic protein (GFAP) expression. These results suggest that low FGF-2 signaling and MASH1 activity can operate in concert to enrich NPC cultures for a GABA neuronal phenotype. When transplanted into the adult rat spinal cord, this combination also yielded GABAergic neurons. These findings indicate that, even for successful utilization of the default GABAergic neuronal precursor fate, a combination of both extrinsic and intrinsic manipulations will likely be necessary to realize the full potential of NSC grafts in restoring function.

Amygdalar GABAergic-rich neural grafts attenuate anxiety-like behavior in rats

Transplantation experiments have shown that neurologic deficits may be reversed by engrafting fresh tissue or engineered cells within dysfunctional neural circuitry. In experimental and clinical settings, this approach has provided insights into the pathology and treatment of neurologic diseases, primarily movement disorders. The present experiments were designed to investigate whether a similar strategy is feasible as a method to investigate, and perhaps repair, circuitry integral to emotional disorders. We focused on the amygdala, a macrostructure known to be involved in the expression of anxiety- and fear-related behaviors. GABAergic cell-rich suspensions were prepared from E17 rat lateral ganglionic eminence and engrafted bilaterally into the lateral and basolateral amygdaloid nuclei of young adult rats. After 6 weeks, increased numbers of GABAergic neurons were identified in the vicinity of the graft sites, and electron microscopy provided evidence for functional integration of transplanted cells. Rats with these grafts spent more time in the open arms of the elevated-plus maze, consistent with an anxioloytic-like phenotype. These rats were also less sensitive to the unconditioned anxiogenic effects of light on the acoustic startle response, although fear-potentiated startle was not affected, suggesting that the grafts produced an attenuation of unlearned fear but did not affect acquisition of conditioned fear. Our results raise the possibility that distinct components of emotion can be modulated by strategic neural engraftment.

Gene regulatory networks in embryonic stem cells and brain development

Embryonic stem cells (ESCs) are endowed with the ability to generate multiple cell lineages and carry great therapeutic potentials in regenerative medicine. Future application of ESCs in human health and diseases will embark on the delineation of molecular mechanisms that define the biology of ESCs. Here, we discuss how the finite ESC components mediate the intriguing task of brain development and exhibit biomedical potentials to cure diverse neurological disorders.

Intraventricular and intracerebral delivery of anti-epileptic drugs in the kindling model

A means to avoid the pharmacokinetic problems affecting the anti-epileptic drugs may be their direct intracerebroventricular (ICV) or intracerebral delivery. This approach may achieve a greater drug concentration at the epileptogenic area while minimizing it in other brain or systemic areas, and thus it could be an interesting therapeutic alternative in drug-resistant epilepsies. The objective of this article is to review a series of experiments, ranging from actute ICV injection to continuous intracerebral infusion of anti-epileptic drugs or grafting of neurotransmitter producing cells, in experimental models, especially in the kindling model of epilepsy in the rat. Acute ICV injection of phenytoin, phenobarbital or carbamacepine is able to diminish the intensity of kindling seizures, but it is also associated with a high neurologic toxicity, especially phenobarbital. Continuous ICV infusion of anti-epileptic drugs can effectively control seizures, but neurologic toxicity is not improved compared with systemic delivery. However, systemic toxicity may be improved, as in the case of valproic acid, whose continuous ICV infusion results in very low plasmatic or hepatic drug concentrations. Continuous intracerebral infusion at the epileptogenic area was studied as an alternative to minimize neurologic toxicity. Thus, intra-amygdalar infusion of gamma-aminobutyric acid (GABA) controls seizures with minimal neurotoxicity in amygdala-kindled rats. Similarly, continuous infusion of GABA into the dorsomedian nucleus of the thalamus improves seizure spread, while not affecting the local epileptogenic activity at the amygdala. Grafting of GABA releasing cells may reduce kindling parameter severity without behavioral side effects. We may conclude that ICV or intracerebral delivery of anti-epileptic drugs or neurotransmitters may be a useful technique to modulate epilepsy.

Transplantation of GABA-producing cells for seizure control in models of temporal lobe epilepsy

A high percentage of patients with temporal lobe epilepsy (TLE) are refractory to conventional pharmacotherapy. The progressive neurodegenerative processes associated with a lifetime of uncontrolled seizures mandate the development of alternative approaches to treat this disease. Transplantation of inhibitory cells has been suggested as a potential therapeutic strategy to achieve seizure suppression in humans with intractable TLE. Preclinical investigations over 20 years have demonstrated that multiple cell types from several sources can produce anticonvulsant, and antiepileptogenic, effects in animal models of TLE. Transplanting GABA-producing cells, in particular, has been shown to reduce seizures in several well-established models. This review addresses experimentation using different sources of transplantable GABAergic cells, highlighting progress with fetal tissue, neural cell lines, and stem cells. Regardless of the source of the GABAergic cells used in seizure studies, common challenges have emerged. Several variables influence the anticonvulsant potential of GABA-producing cells. For example, tissue availability, graft survival, immunogenicity, tumorigenicity, and varying levels of cell migration, differentiation, and integration into functional circuits and the microenvironment provided by sclerotic tissue all contribute to the efficacy of transplanted cells. The challenge of understanding how all of these variables work in concert, in a disease process that has no well-established etiology, suggests that there is still much basic research to be done before rational cell-based therapies can be developed for TLE.

Embryonic stem cell-derived neural precursor grafts for treatment of temporal lobe epilepsy

Complex partial seizures arising from mesial temporal lobe structures are a defining feature of mesial temporal lobe epilepsy (TLE). For many TLE patients, there is an initial traumatic head injury that is the precipitating cause of epilepsy. Severe TLE can be associated with neuropathological changes, including hippocampal sclerosis, neurodegeneration in the dentate gyrus, and extensive reorganization of hippocampal circuits. Learning disabilities and psychiatric conditions may also occur in patients with severe TLE for whom conventional anti-epileptic drugs are ineffective. Novel treatments are needed to limit or repair neuronal damage, particularly to hippocampus and related limbic regions in severe TLE and to suppress temporal lobe seizures. A promising therapeutic strategy may be to restore inhibition of dentate gyrus granule neurons by means of cell grafts of embryonic stem cell-derived GABAergic neuron precursors. "Proof-of-concept" studies show that human and mouse embryonic stem cell-derived neural precursors can survive, migrate, and integrate into the brains of rodents in different experimental models of TLE. In addition, studies have shown that hippocampal grafts of cell lines engineered to release GABA or other anticonvulsant molecules can suppress seizures. Furthermore, transplants of fetal GABAergic progenitors from the mouse or human brain have also been shown to suppress the development of seizures. Here, we review these relevant studies and highlight areas of future research directed toward producing embryonic stem cell-derived GABAergic interneurons for cell-based therapies for treating TLE.

Benefits and risks of intranigral transplantation of GABA-producing cells subsequent to the establishment of kindling-induced seizures

Neural transplantation has been investigated experimentally and clinically for the purpose of developing new treatment options for intractable epilepsy. In the present study we assessed the anticonvulsant efficacy and safety of bilateral allotransplantation of genetically engineered striatal GABAergic rat cell lines into the substantia nigra pars reticulata (SNr). Rats with previously-established seizures, induced by amygdala kindling, were used as a model of temporal lobe epilepsy. Three cell lines were transplanted: (1) immortalized GABAergic cells (M213-2O) derived from embryonic rat striatum; (2) M213-2O cells (CL4) transfected with human GAD67 cDNA to obtain higher GABA synthesis than the parent cell line; and (3) control cells (121-1I), also derived from embryonic rat striatum, but which did not show GAD expression. A second control group received injections of medium alone. Transplantation of M213-2O cells into the SNr of kindled rats resulted in significant but transient anticonvulsant effects. Neither control cells nor medium induced anticonvulsant effects. Strong tissue reactions were, however, induced in the host brain of kindled but not of non-kindled rats, and only in animals that received grafts of genetically modified CL4 cells. These tissue reactions included graft rejection, massive infiltration of inflammatory immune cells, and gliosis. The anticonvulsant effect of M213-2O cells emphasizes the feasibility of local manipulations of seizures by intranigral transplantation of GABA-producing cells. On the other hand, the present data suggest that kindling-induced activation of microglia in the SNr can enhance immune reactions to transplanted cells. In this case, under conditions of further immunological stimulation by CL4 cells, transfected with a human cDNA, substantial immune reactions occurred. Thus, it appears that the condition of the host brain and the production of foreign proteins by transplanted cells have to be considered in estimating the risks of rejection of transplants into the brain.

Gene therapy in epilepsy

Results from animal models suggest gene therapy is a promising new approach for the treatment of epilepsy. Several candidate genes such as neuropeptide Y and galanin have been demonstrated in preclinical studies to have a positive effect on seizure activity. For a successful gene therapy-based treatment, efficient delivery of a transgene to target neurons is also essential. To this end, advances have been made in the areas of cell transplantation and in the development of recombinant viral vectors for gene delivery. Recombinant adeno-associated viral (rAAV) vectors in particular show promise for gene therapy of neurological disorders due to their neuronal tropism, lack of toxicity, and stable persistence in neurons, which results in robust, long-term expression of the transgene. rAAV vectors have been recently used in phase I clinical trials of Parkinson's disease with an excellent safety profile. Prior to commencement of phase I trials for gene therapy of epilepsy, further preclinical studies are ongoing including evaluation of the therapeutic benefit in chronic models of epileptogenesis, as well as assessment of safety in toxicological studies.

Grafting of striatal precursor cells into hippocampus shortly after status epilepticus restrains chronic temporal lobe epilepsy

Status epilepticus (SE) typically progresses into temporal lobe epilepsy (TLE) typified by complex partial seizures. Because sizable fraction of patients with TLE exhibit chronic seizures that are resistant to antiepileptic drugs, alternative therapies that are efficient for diminishing SE-induced chronic epilepsy have great significance. We hypothesize that bilateral grafting of appropriately treated striatal precursor cells into hippocampi shortly after SE is efficacious for diminishing SE-induced chronic epilepsy through long-term survival and differentiation into GABA-ergic neurons. We induced SE in adult rats via graded intraperitoneal injections of kainic acid, bilaterally placed grafts of striatal precursors (pre-treated with fibroblast growth factor-2 and caspase inhibitor) into hippocampi at 4 days post-SE, and examined long-term effects of grafting on spontaneous recurrent motor seizures (SRMS). Analyses at 9-12 months post-grafting revealed that, the overall frequency of SRMS was 67-89% less than that observed in SE-rats that underwent sham-grafting surgery and epilepsy-only controls. Graft cell survival was approximately 33% of injected cells and approximately 69% of surviving cells differentiated into GABA-ergic neurons, which comprised subclasses expressing calbindin, parvalbumin, calretinin and neuropeptide Y. Grafting considerably preserved hippocampal calbindin but had no effects on aberrant mossy fiber sprouting. The results provide novel evidence that bilateral grafting of appropriately treated striatal precursor cells into hippocampi shortly after SE is proficient for greatly reducing the frequency of SRMS on a long-term basis in the chronic epilepsy period. Presence of a large number of GABA-ergic neurons in grafts further suggests that strengthening of the inhibitory control in host hippocampi likely underlies the beneficial effects mediated by grafts.

Intranigral transplants of a GABAergic cell line produce long-term alleviation of established motor seizures

We have previously shown that intranigral transplants of immortalized GABAergic cells decrease the number of kainic acid-induced seizures [Castillo CG, Mendoza S, Freed WJ, Giordano M. Intranigral transplants of immortalized GABAergic cells decrease the expression of kainic acid-induced seizures in the rat. Behav Brain Res 2006;171:109-15] in an animal model. In the present study, recurrent spontaneous behavioral seizures were established by repeated systemic injections of this excitotoxin into male Sprague-Dawley rats. After the seizures had been established, cells were transplanted into the substantia nigra. Animals with transplants of control cells (without hGAD67 expression) or with sham transplants showed a death rate of more than 40% over the 12 weeks of observation, whereas in animals with M213-2O CL-4 transplants, the death rate was reduced to less than 20%. The M213-2O CL-4 transplants significantly reduced the percentage of animals showing behavioral seizures; animals with these transplants also showed a lower occurrence of stage V seizures than animals in the other groups. In vivo and in vitro analyses provided evidence that the GABAergic cells show sustained expression of both GAD67 and hGAD67 cDNA, as well as increased gamma-aminobutyric acid (GABA) levels in the ventral mesencephalon of transplanted animals. Therefore, transplantation of GABA-producing cells can produce long-term alleviation of behavioral seizures in an animal model.