Prolonged attenuation of amygdala-kindled seizure measures in rats by convection-enhanced delivery of the N-type calcium channel antagonists omega-conotoxin GVIA and omega-conotoxin MVIIA

In-house fabrication of bipolar electrode-cannula assembly for electrical stimulation and drug delivery at the same site in rat brain

Strategies drawn at understanding the functional attributes of specific neural circuits often necessitate electrical stimulation and pharmacological manipulation at the same anatomical site. We describe a simple, inexpensive and reliable method to fabricate a bipolar electrode-cannula assembly for delivery of electric pulses and administration of neuroactive agents at the same site in the rat brain. The assembly consisting of a guide cannula, dummy cannula, internal cannula and bipolar electrode was fabricated using syringe needles, wires and simple electronic components. To test the usefulness of the device, it was implanted on the skull of a rat specifically targeting the posterior ventral tegmental area (pVTA). The rat was conditioned to press the lever in intracranial self-stimulation (ICSS) protocol in an operant chamber. The number of lever presses in a 30 min task was monitored. Intra-pVTA administration with bicuculline (GABA_A receptor antagonist) increased the lever press activity, while muscimol (GABA_A receptor agonist) had opposite effect. The results confirm that the group of neurons responding to the electrical stimulation probably receive GABAergic inputs. The device is light in weight, costs less than a dollar and can be fabricated from readily available components. It can serve a useful purpose in electrically stimulating any given target in the brain - before, during or after pharmacological manipulation at the same locus and may find application in neuropharmacological and neurobehavioral studies.

Bypassing the Blood-Brain Barrier: Direct Intracranial Drug Delivery in Epilepsies

Epilepsies are common chronic neurological diseases characterized by recurrent unprovoked seizures of central origin. The mainstay of treatment involves symptomatic suppression of seizures with systemically applied antiseizure drugs (ASDs). Systemic pharmacotherapies for epilepsies are facing two main challenges. First, adverse effects from (often life-long) systemic drug treatment are common, and second, about one-third of patients with epilepsy have seizures refractory to systemic pharmacotherapy. Especially the drug resistance in epilepsies remains an unmet clinical need despite the recent introduction of new ASDs. Apart from other hypotheses, epilepsy-induced alterations of the blood-brain barrier (BBB) are thought to prevent ASDs from entering the brain parenchyma in necessary amounts, thereby being involved in causing drug-resistant epilepsy. Although an invasive procedure, bypassing the BBB by targeted intracranial drug delivery is an attractive approach to circumvent BBB-associated drug resistance mechanisms and to lower the risk of systemic and neurologic adverse effects. Additionally, it offers the possibility of reaching higher local drug concentrations in appropriate target regions while minimizing them in other brain or peripheral areas, as well as using otherwise toxic drugs not suitable for systemic administration. In our review, we give an overview of experimental and clinical studies conducted on direct intracranial drug delivery in epilepsies. We also discuss challenges associated with intracranial pharmacotherapy for epilepsies.

Intracerebroventricular administration of N-type calcium channel blocker ziconotide displays anticonvulsant, anxiolytic, and sedative effects in rats: A preclinical and pilot study

OBJECTIVE

Ziconotide (ω-conotoxin MVIIA peptide) is a novel analgesic agent acting on voltage-gated calcium channels and is administered intrathecally for neuropathic pain. While antiepileptic activities of other types of calcium channel blockers (T- or L-type) are well established, there is no information regarding the effect of ziconotide as an N-type calcium channel antagonist in pentylenetetrazol-induced seizures or its anxiolytic and sedative activities. The present study is the first to report on these effects.

METHODS

To evaluate the anticonvulsant activity of ziconotide in the pentylenetetrazol (60 mg/kg) seizure model, ziconotide was administered intracerebroventricular (i.c.v.) as a single dose (1 μg/rat) or repeatedly (chronic administration: 0.1, 0.3, or 1 μg/rat once a day for seven days). The anxiolytic and sedative actions of ziconotide were evaluated with the elevated plus maze, light/dark (LD) box, and pentobarbital-induced sleep tests. Immediately after behavioral testing, the amygdala was completely removed bilaterally to determine corticosterone levels by immunoassay.

RESULTS

In all dosing regimens, ziconotide significantly decreased the seizure frequency and also delayed the latency period compared with control. Chronic administration affected the percentage of mortality protection, while a single dose of ziconotide did not. In behavioral tests, ziconotide significantly increased both the number of entries and the percentage of time spent in the open arms of the elevated plus maze. Furthermore, ziconotide significantly increased the latency period and the number of entries into the light compartment during the LD box examination. Chronic administration of ziconotide significantly reduced the latency to sleep and increased sleeping time, whereas these parameters were not affected by a single dose. Additionally, amygdala corticosterone levels were significantly decreased in rats treated with ziconotide compared with control.

CONCLUSION

Ziconotide displays beneficial neurobehavioral effects in a model of epilepsy with anxiety as its comorbid event. It seems that at least one of the mechanisms involved in these effects is associated with a decrease in brain corticosterone levels. The main advantage of ziconotide over benzodiazepines (routine anxiolytic and sedative drugs) is that it does not cause tolerance, dependency, and addiction. Therefore, more than ever, it is necessary to improve the convenience of drug delivery protocols and attenuate the adverse effects associated with ziconotide-based therapies.

Sumatriptan reduces severity of status epilepticus induced by lithium-pilocarpine through nitrergic transmission and 5-HT1B/D receptors in rats: A pharmacological-based evidence

Status epilepticus (SE) is a life-threatening neurologic disorder that can be as both cause and consequence of neuroinflammation. In addition to previous reports on anti-inflammatory property of the anti-migraine medication sumatriptan, we have recently shown its anticonvulsive effects on pentylenetetrazole-induced seizure in mice. In the present study, we investigated further (i) the effects of sumatriptan in the lithium-pilocarpine SE model in rats, and (ii) the possible involvement of nitric oxide (NO), 5-hydroxytryptamin 1B/1D (5-HT_1B/1D ) receptor, and inflammatory pathways in such effects of sumatriptan. Status epilepticus was induced by lithium chloride (127 mg/kg, i.p) and pilocarpine (60 mg/kg, i.p.) in Wistar rats. While SE induction increased SE scores and mortality rate, sumatriptan (0.001-1 mg/kg, i.p.) improved it (P < 0.001). Administration of the selective 5-HT_1B/1D antagonist GR-127935 (0.01 mg/kg, i.p.) reversed the anticonvulsive effects of sumatriptan (0.01 mg/kg, i.p.). Although both tumor necrosis factor-α (TNF-α) and NO levels were markedly elevated in the rats' brain tissues post-SE induction, pre-treatment with sumatriptan significantly reduced both TNF-α (P < 0.05) and NO (P < 0.001) levels. Combined GR-127935 and sumatriptan treatment inhibited these anti-inflammatory effects of sumatriptan, whereas combined non-specific NOS (L-NAME) or selective neuronal NOS (7-nitroindazole) inhibitors and sumatriptan further reduced NO levels. In conclusion, sumatriptan exerted a protective effect against the clinical manifestations and mortality rate of SE in rats which is possibly through targeting 5-HT_1B/1D receptors, neuroinflammation, and nitrergic transmission.

TLR3 preconditioning induces anti-inflammatory and anti-ictogenic effects in mice mediated by the IRF3/IFN-β axis

Activation of Toll-like receptor 3 (TLR3) was previously shown to contribute to the generation of epileptic seizures in rodents by evoking a proinflammatory response in the forebrain. This suggests that TLR3 blockade may provide therapeutic effects in epilepsy. We report that brain activation of TLR3 using the synthetic receptor ligand Poly I:C may also result in remarkable dose- and time-dependent inhibitory effects on acute seizures in mice without inducing inflammation. These inhibitory effects are associated with reduced neuronal excitability in the hippocampus as shown by a decrease in the population spike amplitude of CA1 pyramidal neurons following Schaffer collaterals stimulation. TLR3 activation which results in seizure inhibition does not evoke NF-kB-dependent inflammatory molecules or morphological activation of glia, however, it induces the alternative interferon (IFN) regulatory factor (IRF)-3/IFN-β signaling pathway. IFN-β reproduced the inhibitory effects of Poly I:C on neuronal excitability in hippocampal slices. Seizure inhibition attained with activation the TLR3-IRF3/IFN-β axis should be carefully considered when TLR3 are targeted for therapeutic purposes.

Convection-enhanced delivery of botulinum toxin serotype A into the nonhuman primate cisterna magna and hippocampus

OBJECTIVE

Botulinum toxin serotype A (BoNT/A) was reported to raise the seizure threshold when injected into the seizure focus of a kindled rodent model. Delivering BoNT/A to the nonhuman primate (NHP) central nervous system via convection-enhanced delivery (CED) has not been performed. The objective of this study was to determine the toxicity and distribution characteristics of CED of BoNT/A into the NHP hippocampus and cisterna magna.

METHODS

Escalating BoNT/A doses were delivered by CED into the NHP hippocampus (n = 4) and cisterna magna (n = 5) for behavioral and histological assessment and to determine the highest nonlethal dose (LD0) and median lethal dose (LD50). Hippocampal BoNT/A was coinfused with Gd-albumin, a surrogate MRI tracer. Gd-albumin and radioiodinated BoNT/A (125I-BoNT/A) were coinfused into the hippocampus of 3 additional NHPs to determine BoNT/A distribution by in vivo MRI and postmortem quantitative autoradiography. Scintillation counting of CSF assessed the flow of 125I-BoNT/A from the hippocampus to CSF postinfusion.

RESULTS

LD0 and LD50 were 4.2 and 18 ng/kg, and 5 and > 5 ng/kg for the NHP hippocampus and cisterna magna, respectively. Gd-albumin and 125I-BoNT/A completely perfused the hippocampus (155-234 mm3) in 4 of 7 NHPs. Fifteen percent of BoNT/A entered CSF after hippocampal infusion. The MRI distribution volume of coinfused Gd-albumin (VdMRI) was similar to the quantitative autoradiography distribution of 125I-BoNT/A (VdQAR) (mean VdMRI = 139.5 mm3 [n = 7]; VdQAR = 134.8 mm3 [n = 3]; r = 1.00, p < 0.0001). No infusion-related toxicity was identified histologically except that directly attributable to needle placement.

CONCLUSIONS

Gd-albumin accurately tracked BoNT/A distribution on MRI. BoNT/A did not produce CNS toxicity. BoNT/A LD0 exceeded 10-fold the dose administered safely to humans for cosmesis and dystonia.

TAT-Modified ω-Conotoxin MVIIA for Crossing the Blood-Brain Barrier

As the first in a new class of non-opioid drugs, ω-Conotoxin MVIIA was approved for the management of severe chronic pains in patients who are unresponsive to opioid therapy. Unfortunately, clinical application of MVIIA is severely limited due to its poor ability to penetrate the blood-brain barrier (BBB), reaching the central nervous system (CNS). In the present study, we have attempted to increase MVIIA’s ability to cross the BBB via a fusion protein strategy. Our results showed that when the TAT-transducing domain was fused to the MVIIA C-terminal with a linker of varied numbers of glycine, the MVIIA-TAT fusion peptide exhibited remarkable ability to cross the bio-membranes. Most importantly, both intravenous and intranasal administrations of MVIIA-TAT in vivo showed therapeutic efficacy of analgesia. Compared to the analgesic effects of intracerebral administration of the nascent MVIIA, these systemic administrations of MVIIA-TAT require higher doses, but have much prolonged effects. Taken together, our results showed that TAT conjugation of MVIIA not only enables its peripheral administration, but also maintains its analgesic efficiency with a prolonged effective time window. Intranasal administration also rendered the MVIIA-TAT advantages of easy applications with potentially reduced side effects. Our results may present an alternative strategy to improve the CNS accessibility for neural active peptides.

Anticonvulsant Effects of Fractions Isolated from Dinoponera quadriceps (Kempt) Ant Venom (Formicidae: Ponerinae)

Natural products, sources of new pharmacological substances, have large chemical diversity and architectural complexity. In this context, some toxins obtained from invertebrate venoms have anticonvulsant effects. Epilepsy is a neurological disorder that affects about 65 million people worldwide, and approximately 30% of cases are resistant to pharmacological treatment. Previous studies from our group show that the denatured venom of the ant Dinoponera quadriceps (Kempt) protects mice against bicuculline (BIC)-induced seizures and death. The aim of this study was to investigate the anticonvulsant activity of compounds isolated from D. quadriceps venom against seizures induced by BIC in mice. Crude venom was fractionated by high-performance liquid chromatography (HPLC) resulting in six fractions referred to as DqTx1-DqTx6. A liquid chromatography-mass spectrometry (LC/MS) analysis revealed a major 431 Da compound in fractions DqTx1 and DqTx2. Fractions DqTx3 and DqTx4 showed a compound of 2451 Da and DqTx5 revealed a 2436 Da compound. Furthermore, the DqTx6 fraction exhibited a major component with a molecular weight of 13,196 Da. Each fraction (1 mg/mL) was microinjected into the lateral ventricle of mice, and the animals were observed in an open field. We did not observe behavioral alterations when the fractions were given alone. Conversely, when the fractions were microinjected 20 min prior to the administration of BIC (21.6 nM), DqTx1, DqTx4, and DqTx6 fractions increased the latency for onset of tonic-clonic seizures. Moreover, all fractions, except DqTx5, increased latency to death. The more relevant result was obtained with the DqTx6 fraction, which protected 62.5% of the animals against tonic-clonic seizures. Furthermore, this fraction protected 100% of the animals from seizure episodes followed by death. Taken together, these findings indicate that compounds from ant venom might be a potential source of new anticonvulsants molecules.

Blockade of the IL-1R1/TLR4 pathway mediates disease-modification therapeutic effects in a model of acquired epilepsy

We recently discovered that forebrain activation of the IL-1 receptor/Toll-like receptor (IL-1R1/TLR4) innate immunity signal plays a pivotal role in neuronal hyperexcitability underlying seizures in rodents. Since this pathway is activated in neurons and glia in human epileptogenic foci, it represents a potential target for developing drugs interfering with the mechanisms of epileptogenesis that lead to spontaneous seizures. The lack of such drugs represents a major unmet clinical need. We tested therefore novel therapies inhibiting the IL-1R1/TLR4 signaling in an established murine model of acquired epilepsy. We used an epigenetic approach by injecting a synthetic mimic of micro(mi)RNA-146a that impairs IL1R1/TLR4 signal transduction, or we blocked receptor activation with antiinflammatory drugs. Both interventions when transiently applied to mice after epilepsy onset, prevented disease progression and dramatically reduced chronic seizure recurrence, while the anticonvulsant drug carbamazepine was ineffective. We conclude that IL-1R1/TLR4 is a novel potential therapeutic target for attaining disease-modifications in patients with diagnosed epilepsy.

Molecular basis of toxicity of N-type calcium channel inhibitor MVIIA

MVIIA (ziconotide) is a specific inhibitor of N-type calcium channel, Cav2.2. It is derived from Cone snail and currently used for the treatment of severe chronic pains in patients unresponsive to opioid therapy. However, MVIIA produces severe side-effects, including dizziness, nystagmus, somnolence, abnormal gait, and ataxia, that limit its wider application. We previously identified a novel inhibitor of Cav2.2, ω-conopeptide SO-3, which possesses similar structure and analgesic activity to MVIIA's. To investigate the key residues for MVIIA toxicity, MVIIA/SO-3 hybrids and MVIIA variants carrying mutations in its loop 2 were synthesized. The substitution of MVIIA's loop 1 with the loop 1 of SO-3 resulted in significantly reduced Cav2.2 binding activity in vitro; the replacement of MVIIA loop 2 by the loop 2 of SO-3 not only enhanced the peptide/Cav2.2 binding but also decreased its toxicity on goldfish, attenuated mouse tremor symptom, spontaneous locomotor activity, and coordinated locomotion function. Further mutation analysis and molecular calculation revealed that the toxicity of MVIIA mainly arose from Met(12) in the loop 2, and this residue inserts into a hydrophobic hole (Ile(300), Phe(302) and Leu(305)) located between repeats II and III of Cav2.2. The combinative mutations of the loop 2 of MVIIA or other ω-conopeptides may be used for future development of more effective Cav2.2 inhibitors with lower side effects.

Pro- and Anticonvulsant Effects of the Ant Dinoponera quadriceps (Kempf) Venom in Mice

Epilepsy affects at least 50 million people worldwide, and the available treatment is associated with various side effects. Approximately 20-30% of the patients develop seizures that persist despite careful monitored treatment with antiepileptic drugs. Thus, there is a clear need for the development of new antiepileptic drugs, and the venoms can be an excellent source of probes. In this context, while there are studies on venoms from snakes, scorpions, and spiders, little is known regarding venom from ants. The aim of this study was to investigate the potential pro- and anticonvulsant effects of the venom from the ant Dinoponera quadriceps (Kempf) in Swiss mice. After the injection of the crude venom (DqTx-5, 50, and 500 mg/mL) in the lateral ventricle of mice, we observed a reduction of exploration and grooming behaviors, as well as an increase in immobility duration. In addition, the crude venom induced procursive behavior and tonic-clonic seizures at the highest concentration. Conversely, the preadministration of the denatured venom (AbDq) at the concentration of 2 mg/mL protected the animals against tonic-clonic seizures (66.7%) and death (100%) induced by administration of bicuculline. Taken together, the findings demonstrate that D. quadriceps venom might be potential source of new pro- and anticonvulsants molecules.

On-demand pulsatile intracerebral delivery of carisbamate with closed-loop direct neurostimulation therapy in an electrically induced self-sustained focal-onset epilepsy rat model

OBJECT

The authors evaluated the preclinical feasibility of acutely stabilizing an active bihemispheric limbic epileptic circuit using closed-loop direct neurostimulation therapy in tandem with "on-demand'" convection-enhanced intracerebral delivery of the antiepileptic drug (AED) carisbamate. A rat model of electrically induced self-sustained focal-onset epilepsy was employed.

METHODS

A 16-contact depth-recording microelectrode was implanted bilaterally in the dentate gyrus (DG) of the hippocampus of Fischer 344 rats. The right microelectrode array included an integrated microcatheter for drug delivery at the distal tip. Bihemispheric spontaneous self-sustained limbic status epilepticus (SSLSE) was induced in freely moving rats using a 90-minute stimulation paradigm delivered to the right medial perforant white matter pathway. Immediately following SSLSE induction, closed-loop right PP stimulation therapy concurrent with on-demand nanoboluses of the AED [(14)C]-carisbamate (n = 4), or on-demand [(14)C]-carisbamate alone (n = 4), was introduced for a mean of 10 hours. In addition, 2 reference groups received either closed-loop stimulation therapy alone (n = 4) or stimulation therapy with saline vehicle only (n = 4). All animals were sacrificed after completing the specified therapy regimen. In situ [(14)C]-autoradiography was used to determine AED distribution.

RESULTS

Closed-loop direct stimulation therapy delivered unilaterally in the right PP aborted ictal runs detected in either ipsi- or contralateral hippocampi. Freely moving rats receiving closed-loop direct stimulation therapy with ondemand intracerebral carisbamate delivery experienced a significant reduction in seizure frequency (p < 0.001) and minimized seizure frequency variability during the final 50% of the therapy/recording session compared with closed-loop stimulation therapy alone.

CONCLUSIONS

Unilateral closed-loop direct stimulation therapy delivered to afferent hippocampal white matter pathways concurrent with on-demand ipsilateral intracerebral delivery of nano-bolused carisbamate can rapidly decrease the frequency of electrographic seizures in an active bihemispheric epileptic network. Additionally, direct pulsatile delivery of carisbamate can stabilize seizure frequency variability compared with direct stimulation therapy alone.

Future of epilepsy treatment: integration of devices

ABSTRACT 

The use of devices in the treatment of epilepsy is an emerging therapy for those patients whose seizures are not controlled by medications. This article will discuss current treatment options with devices for vagus nerve stimulation, deep brain stimulation and responsive neurostimulation. Emerging therapies in noninvasive neurostimulation such as with trigeminal nerve stimulation, transcranial magnetic stimulation and transcranial direct current stimulation may prove to be promising solutions. Finally, new and enhanced techniques of drug delivery are discussed as well as other devices with potential use in the study and treatment of epilepsy.

Long-lasting attenuation of amygdala-kindled seizures after convection-enhanced delivery of botulinum neurotoxins a and B into the amygdala in rats

Botulinum neurotoxins (BoNTs) are well recognized to cause potent, selective, and long-lasting neuroparalytic actions by blocking cholinergic neurotransmission to muscles and glands. There is evidence that BoNT isoforms can also inhibit neurotransmission in the brain. In this study, we examined whether locally delivered BoNT/A and BoNT/B can attenuate kindling measures in amygdala-kindled rats. Male rats were implanted with a combination infusion cannula-stimulating electrode assembly into the right basolateral amygdala. Fully kindled animals received a single infusion of vehicle or BoNT/A or BoNT/B at doses of 1, 3.2, or 10 ng over a 20-minute period by convection-enhanced delivery. Electrographic (EEG) and behavioral kindling measures were determined at selected times during the 3- to 64-day period after the infusion. BoNT/B produced a dose-dependent elevation in after-discharge threshold and duration and a reduction in the seizure stage and duration of behavioral seizures that lasted for up to 50 days after infusion. BoNT/A had similar effects on EEG measures; behavioral seizure measures were also reduced, but the effect did not reach statistical significance. The effects of both toxins on EEG and behavioral measures progressively resolved during the latter half of the observation period. Animals gained weight normally, maintained normal body temperature, and did not show altered behavior. This study demonstrates for the first time that locally delivered BoNTs can produce prolonged inhibition of brain excitability, indicating that they could be useful for the treatment of brain disorders, including epilepsy, that would benefit from long-lasting suppression of neurotransmission within a circumscribed brain region.

Conotoxins that confer therapeutic possibilities

Cone snails produce a distinctive repertoire of venom peptides that are used both as a defense mechanism and also to facilitate the immobilization and digestion of prey. These peptides target a wide variety of voltage- and ligand-gated ion channels, which make them an invaluable resource for studying the properties of these ion channels in normal and diseased states, as well as being a collection of compounds of potential pharmacological use in their own right. Examples include the United States Food and Drug Administration (FDA) approved pharmaceutical drug, Ziconotide (Prialt^®; Elan Pharmaceuticals, Inc.) that is the synthetic equivalent of the naturally occurring ω-conotoxin MVIIA, whilst several other conotoxins are currently being used as standard research tools and screened as potential therapeutic drugs in pre-clinical or clinical trials. These developments highlight the importance of driving conotoxin-related research. A PubMed query from 1 January 2007 to 31 August 2011 combined with hand-curation of the retrieved articles allowed for the collation of 98 recently identified conotoxins with therapeutic potential which are selectively discussed in this review. Protein sequence similarity analysis tentatively assigned uncharacterized conotoxins to predicted functional classes. Furthermore, conotoxin therapeutic potential for neurodegenerative disorders (NDD) was also inferred.

Therapeutic devices for epilepsy

Therapeutic devices provide new options for treating drug-resistant epilepsy. These devices act by a variety of mechanisms to modulate neuronal activity. Only vagus nerve stimulation (VNS), which continues to develop new technology, is approved for use in the United States. Deep brain stimulation of anterior thalamus for partial epilepsy recently was approved in Europe and several other countries. Responsive neurostimulation, which delivers stimuli to 1 or 2 seizure foci in response to a detected seizure, recently completed a successful multicenter trial. Several other trials of brain stimulation are in planning or underway. Transcutaneous magnetic stimulation (TMS) may provide a noninvasive method to stimulate cortex. Controlled studies of TMS are split on efficacy, which may depend on whether a seizure focus is near a possible region for stimulation. Seizure detection devices in the form of shake detectors via portable accelerometers can provide notification of an ongoing tonic-clonic seizure, or peace of mind in the absence of notification. Prediction of seizures from various aspects of electroencephalography (EEG) is in early stages. Prediction appears to be possible in a subpopulation of people with refractory seizures, and a clinical trial of an implantable prediction device is underway. Cooling of neocortex or hippocampus reversibly can attenuate epileptiform EEG activity and seizures, but engineering problems remain in its implementation. Optogenetics is a new technique that can control excitability of specific populations of neurons with light. Inhibition of epileptiform activity has been demonstrated in hippocampal slices, but use in humans will require more work. In general, devices provide useful palliation for otherwise uncontrollable seizures, but with a different risk profile than with most drugs. Optimizing the place of devices in therapy for epilepsy will require further development and clinical experience.

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.

Anticonvulsant and proconvulsant actions of 2-deoxy-D-glucose

PURPOSE

2-Deoxy-D-glucose (2-DG), a glucose analog that accumulates in cells and interferes with carbohydrate metabolism by inhibiting glycolytic enzymes, has anticonvulsant actions. Recognizing that severe glucose deprivation can induce seizures, we sought to determine whether acute treatment with 2-DG can promote seizure susceptibility by assessing its effects on seizure threshold. For comparison, we studied 3-methyl-glucose (3-MG), which like 2-DG accumulates in cells and reduces glucose uptake, but does not inhibit glycolysis.

METHODS

Mice were treated with 2-DG or 3-MG and the seizure threshold determined in the 6-Hz test, the mouse electroshock seizure threshold (MEST) test, and the intravenous pentylenetetrazol (i.v. PTZ) or kainic acid (i.v. KA) seizure threshold tests. 2-DG was also tested in fully amygdala-kindled rats.

RESULTS

2-DG (125-500 mg/kg, i.p., 30 min before testing) significantly elevated the seizure threshold in the 6-Hz seizure test. 2-DG (250-500 mg/kg) decreased the threshold in the MEST and i.v. PTZ and i.v. KA tests. 3-MG had no effect on seizure threshold in the 6-Hz test but, like 2-DG, decreased seizure threshold in the i.v. PTZ test. 2-DG (250 and 500 mg/kg, i.p., 30 min before testing) had no effect on amygdala-kindled seizures.

CONCLUSIONS

Although 2-DG protects against seizures in the 6-Hz seizure test, it promotes seizures in some other models. The proconvulsant action may relate to reduced glucose uptake, whereas the anticonvulsant action may require inhibition of glycolysis and shunting of glucose metabolism through the pentose phosphate pathway.

Various drug delivery approaches to the central nervous system

IMPORTANCE OF THE FIELD

The presence of the blood-brain barrier (BBB), an insurmountable obstacle, in particular, and other barriers in brain and periphery contribute to hindrance of the successful diagnosis and treatment of a myriad of central nervous system pathologies. This review discusses several strategies adopted to define a rational drug delivery approach to the CNS along with a short description of the strategies implemented by the authors' group to enhance the analgesic activity, a CNS property, of chimeric peptide of Met-enkephalin and FMRFa (YGGFMKKKFMRFa-YFa).

AREAS COVERED IN THIS REVIEW

Various approaches for drug delivery to the CNS with their beneficial and non-beneficial aspects, supported by an extensive literature survey published recently, up to August 2009.

WHAT THE READER WILL GAIN

The reader will have the privilege of gaining an understanding of previous as well as recent approaches to breaching the CNS barriers.

TAKE HOME MESSAGE

Among the various strategies discussed, the potential for efficacious CNS drug targeting in future lies either with the non-invasively administered multifunctional nanosystems or these nanosystems without characterstics such as long systemic circulating capability and avoiding reticuloendothelial system scavenging system of the body, endogenous transporters and efflux inhibitors administered by convection-enhanced delivery.

Evolution and prospects for intracranial pharmacotherapy for refractory epilepsies: the subdural hybrid neuroprosthesis

Intracranial pharmacotherapy is a novel strategy to treat drug refractory, localization-related epilepsies not amenable to resective surgery. The common feature of the method is the use of some type of antiepileptic drug (AED) delivery device placed inside the cranium to prevent or stop focal seizures. This distinguishes it from other nonconventional methods, such as intrathecal pharmacotherapy, electrical neurostimulation, gene therapy, cell transplantation, and local cooling. AED-delivery systems comprise drug releasing polymers and neuroprosthetic devices that can deliver AEDs into the brain via intraparenchymal, ventricular, or transmeningeal routes. One such device is the subdural Hybrid Neuroprosthesis (HNP), designed to deliver AEDs, such as muscimol, into the subdural/subarachnoid space overlaying neocortical epileptogenic zones, with electrophysiological feedback from the treated tissue. The idea of intracranial pharmacotherapy and HNP treatment for epilepsy originated from multiple sources, including the advent of implanted medical devices, safety data for intracranial electrodes and catheters, evidence for the seizure-controlling efficacy of intracerebral AEDs, and further understanding of the pathophysiology of focal epilepsy. Successful introduction of intracranial pharmacotherapy into clinical practice depends on how the intertwined scientific, engineering, clinical, neurosurgical and regulatory challenges will be met to produce an effective and commercially viable device.

Convection-enhanced delivery for the treatment of brain tumors

The brain is highly accessible for nutrients and oxygen, however delivery of drugs to malignant brain tumors is a very challenging task. Convection-enhanced delivery (CED) has been designed to overcome some of the difficulties so that pharmacological agents that would not normally cross the BBB can be used for treatment. Drugs are delivered through one to several catheters placed stereotactically directly within the tumor mass or around the tumor or the resection cavity. Several classes of drugs are amenable to this technology including standard chemotherapeutics or novel experimental targeted drugs. The first Phase III trial for CED-delivered, molecularly targeted cytotoxin in the treatment of recurrent glioblastoma multiforme has been accomplished and demonstrated objective clinical efficacy. The lessons learned from more than a decade of attempts at exploiting CED for brain cancer treatment weigh critically for its future clinical applications. The main issues center around the type of catheters used, number of catheters and their exact placement; pharmacological formulation of drugs, prescreening patients undergoing treatment and monitoring the distribution of drugs in tumors and the tumor-infiltrated brain. It is expected that optimizing CED will make this technology a permanent addition to clinical management of brain malignancies.

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.

Convection-enhanced delivery in the treatment of epilepsy

Convection-enhanced delivery (CED) is a novel drug-delivery technique that uses positive hydrostatic pressure to deliver a fluid containing a therapeutic substance by bulk flow directly into the interstitial space within a localized region of the brain parenchyma. CED circumvents the blood-brain barrier and provides a wider, more homogenous distribution than bolus deposition (focal injection) or other diffusion-based delivery approaches. A potential use of CED is for the local delivery of antiseizure agents, which would provide an epilepsy treatment approach that avoids the systemic toxicities of orally administered antiepileptic drugs and bystander effects on nonepileptic brain regions. Recent studies have demonstrated that brief CED infusions of nondiffusible peptides that inhibit the release of excitatory neurotransmitters, including omega-conotoxins and botulinum neurotoxins, can produce long-lasting (weeks to months) seizure protection in the rat amygdala-kindling model. Seizure protection is obtainable without detectable neurological or behavioral side effects. Although conventional diffusible antiepileptic drugs do confer seizure protection when administered locally by CED, the effect is transitory. CED is a potential approach for seizure protection that could represent an alternative to resective surgery in the treatment of focal epilepsies that are resistant to orally-administered antiepileptic drugs. The prolonged duration of action of nondiffusible toxins would allow seizure protection to be maintained chronically with infrequent reinfusions.

Nanotechnology for delivery of drugs to the brain for epilepsy

Epilepsy results from aberrant electrical activity that can affect either a focal area or the entire brain. In treating epilepsy with drugs, the aim is to decrease seizure frequency and severity while minimizing toxicity to the brain and other tissues. Antiepileptic drugs (AEDs) are usually administered by oral and intravenous routes, but these drug treatments are not always effective. Drug access to the brain is severely limited by a number of biological factors, particularly the blood-brain barrier, which impedes the ability of AEDs to enter and remain in the brain. To improve the efficacy of AEDs, new drug delivery strategies are being developed; these methods fall into the three main categories: drug modification, blood-brain barrier modification, and direct drug delivery. Recently, all three methods have been improved through the use of drug-loaded nanoparticles.