GABAA currents are decreased by IL-1β in epileptogenic tissue of patients with temporal lobe epilepsy: implications for ictogenesis

Inhibition of P2X7 Receptor Ameliorates Nuclear Factor-Kappa B Mediated Neuroinflammation Induced by Status Epilepticus in Rat Hippocampus

P2X7 receptor (P2X7R) has been reported participating in neuroinflammation in multiple neurological diseases. We explored the role of P2X7R in a rat status epilepticus (SE) model induced by coriaria lactone (CL) and its association with neuroinflammation. Thirty minutes after intracerebroventricular infusion with P2X7R antagonists Brilliant blue G (BBG), A-438079, A-740003, or agonists 2',3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP), SE was induced by intramuscular injection of CL in Sprague-Dawley rats. Seizures severity was recorded according to the Racine scale and Morris water maze test was performed. P2X7R expression was measured by western blotting. Immunohistochemical staining was performed to assess pro-inflammation cytokines expression, neuronal loss, and astrocyte activation. The results showed P2X7R level began to increase at 1 day, peaked at 2 days, and gradually decreased to baseline by 2 weeks in rat hippocampus after SE. P2X7R activation induced NF-κB phosphorylation, along with increased IL-1β and IL-6 expression. Pretreatment with P2X7R antagonists ameliorated SE-induced neuroinflammation, neuronal damage, and astroglial and microglial activation to variable extent. In addition, these antagonists ameliorated seizure severity and improved cognitive function. These findings suggest P2X7R activation plays a critical role in epileptogenesis via regulation of neuroinflammation and blocking P2X7R may be a novel therapeutic strategy for epilepsy.

Inflammatory cytokine-induced changes in neural network activity measured by waveform analysis of high-content calcium imaging in murine cortical neurons

During acute neuroinflammation, increased levels of cytokines within the brain may contribute to synaptic reorganization that results in long-term changes in network hyperexcitability. Indeed, inflammatory cytokines are implicated in synaptic dysfunction in epilepsy and in an array of degenerative and autoimmune diseases of the central nervous system. Current tools for studying the impact of inflammatory factors on neural networks are either insufficiently fast and sensitive or require complicated and costly experimental rigs. Calcium imaging offers a reasonable surrogate for direct measurement of neuronal network activity, but traditional imaging paradigms are confounded by cellular heterogeneity and cannot readily distinguish between glial and neuronal calcium transients. While the establishment of pure neuron cultures is possible, the removal of glial cells ignores physiologically relevant cell-cell interactions that may be critical for circuit level disruptions induced by inflammatory factors. To overcome these issues, we provide techniques and algorithms for image processing and waveform feature extraction using automated analysis of spontaneous and evoked calcium transients in primary murine cortical neuron cultures transduced with an adeno-associated viral vector driving the GCaMP6f reporter behind a synapsin promoter. Using this system, we provide evidence of network perturbations induced by the inflammatory cytokines TNFα, IL1β, and IFNγ.

Neuroinflammatory targets and treatments for epilepsy validated in experimental models

A large body of evidence that has accumulated over the past decade strongly supports the role of inflammation in the pathophysiology of human epilepsy. Specific inflammatory molecules and pathways have been identified that influence various pathologic outcomes in different experimental models of epilepsy. Most importantly, the same inflammatory pathways have also been found in surgically resected brain tissue from patients with treatment-resistant epilepsy. New antiseizure therapies may be derived from these novel potential targets. An essential and crucial question is whether targeting these molecules and pathways may result in anti-ictogenesis, antiepileptogenesis, and/or disease-modification effects. Therefore, preclinical testing in models mimicking relevant aspects of epileptogenesis is needed to guide integrated experimental and clinical trial designs. We discuss the most recent preclinical proof-of-concept studies validating a number of therapeutic approaches against inflammatory mechanisms in animal models that could represent novel avenues for drug development in epilepsy. Finally, we suggest future directions to accelerate preclinical to clinical translation of these recent discoveries.

Chemokines as new inflammatory players in the pathogenesis of epilepsy

A large series of clinical and experimental studies supports a link between inflammation and epilepsy, indicating that inflammatory processes within the brain are important contributors to seizure recurrence and precipitation. Systemic inflammation can precipitate seizures in children suffering from epileptic encephalopathies, and hallmarks of a chronic inflammatory state have been found in patients with temporal lobe epilepsy. Research performed on animal models of epilepsy further corroborates the idea that seizures upregulate inflammatory mediators, which in turn may enhance brain excitability and neuronal degeneration. Several inflammatory molecules and their signaling pathways have been implicated in epilepsy. Among these, the chemokine pathway has increasingly gained attention. Chemokines are small cytokines secreted by blood cells, which act as chemoattractants for leukocyte migration. Recent studies indicate that chemokines and their receptors are also produced by brain cells, and are involved in various neurological disorders including epilepsy. In this review, we will focus on a subset of pro-inflammatory chemokines (namely CCL2, CCL3, CCL5, CX3CL1) and their receptors, and their increasingly recognized role in seizure control.

Aspirin attenuates spontaneous recurrent seizures in the chronically epileptic mice

OBJECTIVE

Neuroinflammatory processes are pathologic hallmarks of both experimental and human epilepsy, and could be implicated in the neuronal hyperexcitability. Aspirin represents one of the non-selective nonsteroidal anti-inflammatory drugs with fewer side effects in long-term application. This study was carried out to assess the anti-epileptic effects of aspirin when administered during the chronic stage of temporal lobe epilepsy [TLE] in mice. The alteration of hippocampal neurogenesis was also examined for raising a possible mechanism underlying the protective effect of anti-inflammatory treatment in the TLE.

METHODS

Two months after pilocarpine-induced status epilepticus, the chronically epileptic mice were treated with aspirin (20 mg, 60 mg or 80 mg/kg) once a day for 10 weeks. Spontaneous recurrent seizures were monitored by video camera for 2 weeks. To evaluate the profile of hippocampal neurogenesis, the newly generated cells in the dentate gyrus were labeled by the proliferation marker BrdU. The newborn neurons that extended axons to CA3 area were visualized by cholera toxin B subunit retrograde tracing.

RESULTS

Administration of aspirin with a dosage of 60 mg or 80 mg/kg initiated at 2 months after pilocarpine-induced status epilepticus significantly reduced the frequency and duration of spontaneous recurrent seizures. Aspirin treatment also increased the number of newborn neurons with anatomic integration through improving the survival of the newly generated cells.

CONCLUSION

Aspirin treatment during the chronic stage of TLE could attenuate the spontaneous recurrent seizures in mice. Promotion of hippocampal neurogenesis and inhibition of COX-PGE2 pathway might partly contribute to this anti-epileptic effect. Highlights • Aspirin attenuates spontaneous recurrent seizures of chronically epileptic mice • Aspirin increases neurogenesis of chronically epileptic hippocampus by improving the survival of newly generated cells • Promotion of hippocampal neurogenesis and inhibition of COX-PGE2 pathway might partly contribute to anti-epileptic effects of aspirin.

Interleukin-1β increases neuronal death in the hippocampal dentate gyrus associated with status epilepticus in the developing rat

BACKGROUND

Interleukin-1β (IL-1β) increases necrotic neuronal cell death in the CA1 area after induced status epilepticus (SE) in developing rats. However, it remains uncertain whether IL-1β has a similar effect on the hippocampal dentate gyrus (DG). In this study, we analysed the effects of IL-1β on 14-day-old Wistar rats experiencing DG neuronal death induced by SE.

METHODS

SE was induced with lithium-pilocarpine. Six hours after SE onset, a group of pups was injected with IL-1β (at 0, 0.3, 3, 30, or 300ng/μL) in the right ventricle; another group was injected with IL-1β receptor (IL-1R1) antagonist (IL-1Ra, at 30ng/μL) of IL-1RI antagonist (IL-1Ra) alone, and additional group with 30ng/μL of IL-1Ra plus 3ng/μL of IL-1β. Twenty-four hours after SE onset, neuronal cell death in the dentate gyrus of the dorsal hippocampus was assessed using haematoxylin-eosin staining. Dead cells showed eosinophilic cytoplasm and condensed and fragmented nuclei.

RESULTS

We observed an increased number of eosinophilic cells in the hippocampal DG ipsilateral to the site of injection of 3ng/μL and 300ng/μL of IL-1β in comparison with the vehicle group. A similar effect was observed in the hippocampal DG contralateral to the site of injection of 3ng/μL of IL-1β. Administration of both of IL-1β and IL-1Ra failed to prevent an increase in the number of eosinophilic cells.

CONCLUSION

Our data suggest that IL-1β increases apoptotic neuronal cell death caused by SE in the hippocampal GD, which is a mechanism independent of IL-1RI activation.

Critical Evaluation of P2X7 Receptor Antagonists in Selected Seizure Models

The ATP-gated P2X7 receptor (P2X7R) is a non-selective cation channel which senses high extracellular ATP concentrations and has been suggested as a target for the treatment of neuroinflammation and neurodegenerative diseases. The use of P2X7R antagonists may therefore be a viable approach for treating CNS pathologies, including epileptic disorders. Recent studies showed anticonvulsant potential of P2X7R antagonists in certain animal models. To extend this work, we tested three CNS-permeable P2X7R blocker (Brilliant Blue G, AFC-5128, JNJ-47965567) and a natural compound derivative (tanshinone IIA sulfonate) in four well-characterized animal seizure models. In the maximal electroshock seizure threshold test and the pentylenetetrazol (PTZ) seizure threshold test in mice, none of the four compounds demonstrated anticonvulsant effects when given alone. Notably, in combination with carbamazepine, both AFC-5128 and JNJ-47965567 increased the threshold in the maximal electroshock seizure test. In the PTZ-kindling model in rats, useful for testing antiepileptogenic activities, Brilliant Blue G and tanshinone exhibited a moderate retarding effect, whereas the potent P2X7R blocker AFC-5128 and JNJ-47965567 showed a significant and long-lasting delay in kindling development. In fully kindled rats, the investigated compounds revealed modest effects to reduce the mean seizure stage. Furthermore, AFC-5128- and JNJ-47965567-treated animals displayed strongly reduced Iba 1 and GFAP immunoreactivity in the hippocampal CA3 region. In summary, our results show that P2X7R antagonists possess no remarkable anticonvulsant effects in the used acute screening tests, but can attenuate chemically-induced kindling. Further studies would be of interest to support the concept that P2X7R signalling plays a crucial role in the pathogenesis of epileptic disorders.

Interleukin-1 receptor is a target for adjunctive control of diazepam-refractory status epilepticus in mice

Proinflammatory cytokine interleukin-1 beta (IL-1β) may accumulate in the brain during status epilepticus, but whether it contributes to the progressive refractoriness of SE remains unclear. By using a kainic acid-induced SE mice model, we tested whether pharmacological blockade or knock-out of interleukin-1 receptor type 1 (IL-1R1) could influence the diazepam-refractory phenomenon of prolonged SE. We confirmed diazepam failed to terminate prolonged SE (allowed to continue for 40min before diazepam administration). The expression level of IL-1β in the hippocampus during prolonged SE was significantly higher than that of baseline. Interestingly, prolonged SE was not diazepam-refractory in IL-1R1 knock-out mice. Moreover, administration of interleukin-1 receptor antagonist (IL-1RA) combined with diazepam terminated established prolonged SE, while IL-1RA alone is not capable to terminate prolonged SE. On the contrary, administration of recombinant human IL-1β weakens the efficacy of diazepam by prolonging its latency to terminate non-prolonged SE. Thus, the present study provides direct evidence that accumulated IL-1β contributed to the diazepam refractoriness of prolonged SE, and suggests that interleukin-1 receptor is a target for adjunctive control of diazepam-refractory SE.

Anti-Inflammatory Small Molecules To Treat Seizures and Epilepsy: From Bench to Bedside

As a crucial component of brain innate immunity, neuroinflammation initially contributes to neuronal tissue repair and maintenance. However, chronic inflammatory processes within the brain and associated blood-brain barrier (BBB) impairment often cause neurotoxicity and hyperexcitability. Mounting evidence points to a mutual facilitation between inflammation and epilepsy, suggesting that blocking the undesired inflammatory signaling within the brain might provide novel strategies to treat seizures and epilepsy. Neuroinflammation is primarily characterized by the upregulation of proinflammatory mediators in epileptogenic foci, among which cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2), interleukin-1β (IL-1β), transforming growth factor-β (TGF-β), toll-like receptor 4 (TLR4), high-mobility group box 1 (HMGB1), and tumor necrosis factor-α (TNF-α) have been extensively studied. Small molecules that specifically target these key proinflammatory perpetrators have been evaluated for antiepileptic and antiepileptogenic effects in animal models. These important preclinical studies provide new insights into the regulation of inflammation in epileptic brains and guide drug discovery efforts aimed at developing novel anti-inflammatory therapies for seizures and epilepsy.

Modulation of neuronal excitability by immune mediators in epilepsy

A complex set of inflammatory molecules and their receptors has been described in epileptogenic foci in different forms of pharmacoresistant epilepsies. By activating receptor-mediated pathways in neurons, these molecules have profound neuromodulatory effects that are distinct from their canonical activation of immune functions. Importantly, the neuromodulatory actions of some inflammatory molecules contribute to hyperexcitability in neural networks that underlie seizures. This review summarizes recent findings related to the role of cytokines (IL-1beta and TNF-alpha) and danger signals (HMGB1) in decreasing seizure threshold, thereby contributing to seizure generation and the associated neuropathology. We will discuss preclinical studies suggesting that pharmacological inhibition of specific inflammatory signals may be useful to treat drug-resistant seizures in human epilepsy, and possibly arrest epileptogenesis in individuals at risk of developing the disease.