Adenosine A1 receptor-mediated suppression of carbamazepine-resistant seizure-like events in human neocortical slices

The role of the adenosine system in epilepsy and its comorbidities

Epilepsy is one of the most serious and common chronic neurological conditions, characterised by recurrent hypersynchronous electrical activity in the brain that lead to seizures. Despite over 50 million people being affected worldwide, only ~70% of people with epilepsy have their seizures successfully controlled with current pharmacotherapy, and many experience significant psychiatric and physical comorbidities. Adenosine, a ubiquitous purine metabolite, is a potent endogenous anti-epileptic substance that can abolish seizure activity via the adenosine A1 G protein-coupled receptor. Activation of A1 receptors decreases seizure activity in animal models, including models of drug-resistant epilepsy. Recent advances have increased our understanding of epilepsy comorbidities, highlighting the potential for adenosine receptors to modulate epilepsy-associated comorbidities, including cardiovascular dysfunction, sleep and cognition. This review provides an accessible resource of the current advances in understanding the adenosine system as a therapeutic target for epilepsy and epilepsy-associated comorbidities. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Bipolar mania and epilepsy pathophysiology and treatment may converge in purine metabolism: A new perspective on available evidence

Decreased ATPergic signaling is an increasingly recognized pathophysiology in bipolar mania disease models. In parallel, adenosine deficit is increasingly recognized in epilepsy pathophysiology. Under-recognized ATP and/or adenosine-increasing mechanisms of several antimanic and antiseizure therapies including lithium, valproate, carbamazepine, and ECT suggest a fundamental pathogenic role of adenosine deficit in bipolar mania to match the established role of adenosine deficit in epilepsy. The depletion of adenosine-derivatives within the purine cycle is expected to result in a compensatory increase in oxopurines (uric acid precursors) and secondarily increased uric acid, observed in both bipolar mania and epilepsy. Cortisol-based inhibition of purine conversion to adenosine-derivatives may be reflected in observed uric acid increases and the well-established contribution of cortisol to both bipolar mania and epilepsy pathology. Cortisol-inhibited conversion from IMP to AMP as precursor of both ATP and adenosine may represent a mechanism for treatment resistance common in both bipolar mania and epilepsy. Anti-cortisol therapies may therefore augment other treatments both in bipolar mania and epilepsy. Evidence linking (i) adenosine deficit with a decreased need for sleep, (ii) IMP/cGMP excess with compulsive hypersexuality, and (iii) guanosine excess with grandiose delusions may converge to suggest a novel theory of bipolar mania as a condition characterized by disrupted purine metabolism. The potential for disease-modification and prevention related to adenosine-mediated epigenetic changes in epilepsy may be mirrored in mania. Evaluating the purinergic effects of existing agents and validating purine dysregulation may improve diagnosis and treatment in bipolar mania and epilepsy and provide specific targets for drug development.

Epileptiform Discharges Reduce Neuronal ATP Production by Inhibiting F0F1-ATP Synthase Activity via A Zinc-α2-Glycoprotein-Dependent Mechanism

Neuronal energy metabolism dysfunction, especially adenosine triphosphate (ATP) supply decrease, is observed in epilepsy and associated with epileptogenesis and prognosis. Zinc-α2-glycoprotein (ZAG) is known as an important modulator of energy metabolism and involved in neuronal glucose metabolism, fatty acid metabolism, and ketogenesis impairment in seizures, but its effect on neuronal ATP synthesis in seizures and the specific mechanism are unclear. In this study, we verified the localization of ZAG in primary cultured neuronal mitochondria by using double-labeling immunofluorescence, immune electron microscopy, and western blot. ZAG level in neuronal mitochondria was modulated by lentiviruses and detected by western blot. The F0F1-ATP synthase activity, ATP level, and acetyl-CoA level were measured. The binding between ZAG and F0F1-ATP synthase was determined by coimmunoprecipitation. We found that both ZAG and F0F1-ATP synthase existed in neuronal mitochondria, and there was mutual binding between them. Epileptiform discharge-induced decrease of mitochondrial ZAG level was reversed by ZAG overexpression. Epileptiform discharge or ZAG knockdown decreased F0F1-ATP synthase activity and ATP level in neurons, which were reversed by ZAG overexpression, while overexpression of ZAG along only increased F0F1-ATP synthase activity but not increased ATP level. Meanwhile, neither epileptiform discharges nor changes of ZAG level can alter the acetyl-CoA level. Moreover, epileptiform discharge did not alter F0F1-ATP synthase level. In conclusion, epileptiform discharge-induced ZAG decrease in neuronal mitochondria is correlated to F0F1-ATP synthase activity inhibition, which may possibly lead to ATP supply impairments. ZAG may be a potential therapeutic target for treating neuronal energy metabolism dysfunction in seizures with further researches.

Reversal of chronic restraint stress-induced memory impairment by Japanese sake yeast supplement in mice: Role of adenosine A1 and A2A receptors

Controversial studies indicate the adenosine compound (a neuromodulator with neuroprotective activity) intervention on cognitive performance. On the other hand, Japanese sake yeast has been enriched with oral adenosine analogs as a novel natural agent. As the first report, we aimed to evaluate the effects of Japanese sake yeast supplement in a mouse model of chronic restraint stress-induced cognitive dysfunction. Mice were subjected to a one-week stress protocol and concomitantly treated orally with sake yeast at the dose level of 100, 200 and 300 mg/kg once daily for a week. The spatial and conditioned fear memory functions were evaluated with the Morris Water Maze (MWM) and the Passive Avoidance Learning (PAL) test, respectively. In all dosing regimens, improvements in spatial cognition were observed significantly in the MWM. 200 and 300 mg/kg of sake yeast significantly improved short- and long-term fear memory functions in the PAL test. Memory-enhancing effect of sake yeast was potentiated by the injection of ZM241385 (15 mg/kg), a selective adenosine A_2A receptor (A_2AR) antagonist, but completely disappeared by the injection of 8-cyclopentyltheophylline (CPT-8, 10 mg/kg), a selective adenosine A₁ receptor (A₁R) antagonist. The findings of the present study demonstrate the efficacy of sake yeast in acting as a cognitive performance-enhancing agent. Eventually, sake yeast and its ingredient S-adenosyl methionine (SAM) may be useful in improving memory in patients suffering from many dementia forms including Alzheimer's disease (AD).

The mechanism of sudden unexpected death in epilepsy: A mini review

Sudden unexpected death in epilepsy (SUDEP) is defined as a sudden, unexpected, non-traumatic, non-drowning death in a person with epilepsy. SUDEP is generally considered to result from seizure-related cardiac dysfunction, respiratory depression, autonomic nervous dysfunction, or brain dysfunction. Frequency of generalized tonic clonic seizures (GTCS), prone posture, and refractory epilepsy are considered risk factors. SUDEP has also been associated with inherited cardiac ion channel disease and severe obstructive sleep apnea. Most previous studies of SUDEP mechanisms have focused on cardiac and respiratory dysfunction and imbalance of the neural regulatory system. Cardiac-related mechanisms include reduction in heart rate variability and prolongation of QT interval, which can lead to arrhythmias. Laryngospasm and amygdala activation may cause obstructive and central apnea, respectively. Neural mechanisms include impairment of 5-HT and adenosine neuromodulation. The research to date regarding molecular mechanisms of SUDEP is relatively limited. Most studies have focused on p-glycoprotein, catecholamines, potassium channels, and the renin-angiotensin system, all of which affect cardiac and respiratory function.

Design, synthesis and evaluation of amino-3,5-dicyanopyridines and thieno[2,3-b]pyridines as ligands of adenosine A1 receptors for the potential treatment of epilepsy

Due to the implication of adenosine in seizure suppression, adenosine-based therapies such as adenosine receptor (AR) agonists have been investigated. This study aimed at investigating thieno[2,3-b]pyridine derivatives as non-nucleoside A₁ agonists that could be used in pharmaco-resistant epilepsy (PRE). Compound 7c (thieno[2,3-b]pyridine derivative), displayed good binding affinity to the rA₁ AR (K_i = 61.9 nM). This could be a breakthrough for further investigation of this heterocyclic scaffold as potential ligand. In silico evaluation of this compound raised bioavailability concerns but performed well on drug-likeness tests. The effect of intramolecular cyclisation that occurs during synthesis of thieno[2,3-b]pyridines from the lead compounds, amino-3,5-dicyanopyridine derivatives (6a-s) in relation to AR binding was also evaluated. A significant loss of activity against rA₁/rA_2A ARs with cyclisation was revealed. Amino-3,5-dicyanopyridines exhibited greater affinity towards rA₁ ARs (K_i < 10 nM) than rA_2A. Compound 6c had the best rA₁ affinity (K_i = 0.076 nM). Novel compounds (6d, 6k, 6l, 6m, 6n, 6o, 6p) were highly selective towards rA₁ AR (K_i between 0.179 and 21.0 nM). Based on their high selectivity for A₁ ARs, amino-3,5-dicyanopyridines may be investigated further as AR ligands in PRE with the right structural optimisations and formulations.

Emerging roles of dysregulated adenosine homeostasis in brain disorders with a specific focus on neurodegenerative diseases

In modern societies, with an increase in the older population, age-related neurodegenerative diseases have progressively become greater socioeconomic burdens. To date, despite the tremendous effort devoted to understanding neurodegenerative diseases in recent decades, treatment to delay disease progression is largely ineffective and is in urgent demand. The development of new strategies targeting these pathological features is a timely topic. It is important to note that most degenerative diseases are associated with the accumulation of specific misfolded proteins, which is facilitated by several common features of neurodegenerative diseases (including poor energy homeostasis and mitochondrial dysfunction). Adenosine is a purine nucleoside and neuromodulator in the brain. It is also an essential component of energy production pathways, cellular metabolism, and gene regulation in brain cells. The levels of intracellular and extracellular adenosine are thus tightly controlled by a handful of proteins (including adenosine metabolic enzymes and transporters) to maintain proper adenosine homeostasis. Notably, disruption of adenosine homeostasis in the brain under various pathophysiological conditions has been documented. In the past two decades, adenosine receptors (particularly A₁ and A_2A adenosine receptors) have been actively investigated as important drug targets in major degenerative diseases. Unfortunately, except for an A_2A antagonist (istradefylline) administered as an adjuvant treatment with levodopa for Parkinson's disease, no effective drug based on adenosine receptors has been developed for neurodegenerative diseases. In this review, we summarize the emerging findings on proteins involved in the control of adenosine homeostasis in the brain and discuss the challenges and future prospects for the development of new therapeutic treatments for neurodegenerative diseases and their associated disorders based on the understanding of adenosine homeostasis.

ATP and adenosine-Two players in the control of seizures and epilepsy development

Despite continuous advances in understanding the underlying pathogenesis of hyperexcitable networks and lowered seizure thresholds, the treatment of epilepsy remains a clinical challenge. Over one third of patients remain resistant to current pharmacological interventions. Moreover, even when effective in suppressing seizures, current medications are merely symptomatic without significantly altering the course of the disease. Much effort is therefore invested in identifying new treatments with novel mechanisms of action, effective in drug-refractory epilepsy patients, and with the potential to modify disease progression. Compelling evidence has demonstrated that the purines, ATP and adenosine, are key mediators of the epileptogenic process. Extracellular ATP concentrations increase dramatically under pathological conditions, where it functions as a ligand at a host of purinergic receptors. ATP, however, also forms a substrate pool for the production of adenosine, via the action of an array of extracellular ATP degrading enzymes. ATP and adenosine have assumed largely opposite roles in coupling neuronal excitability to energy homeostasis in the brain. This review integrates and critically discusses novel findings regarding how ATP and adenosine control seizures and the development of epilepsy. This includes purine receptor P1 and P2-dependent mechanisms, release and reuptake mechanisms, extracellular and intracellular purine metabolism, and emerging receptor-independent effects of purines. Finally, possible purine-based therapeutic strategies for seizure suppression and disease modification are discussed.

The actin binding protein drebrin helps to protect against the development of seizure-like events in the entorhinal cortex

The actin binding protein drebrin plays a key role in dendritic spine formation and synaptic plasticity. Decreased drebrin protein levels have been observed in temporal lobe epilepsy, suggesting the involvement of drebrin in the disease. Here we investigated the effect of drebrin knockout on physiological and pathophysiological neuronal network activities in mice by inducing gamma oscillations, involved in higher cognitive functions, and by analyzing pathophysiological epileptiform activity. We found that loss of drebrin increased the emergence of spontaneous gamma oscillations suggesting an increase in neuronal excitability when drebrin is absent. Further analysis showed that although the kainate-induced hippocampal gamma oscillations were unchanged in drebrin deficient mice, seizure like events measured in the entorhinal cortex appeared earlier and more frequently. The results suggest that while drebrin is not essential for normal physiological network activity, it helps to protect against the formation of seizure like activities during pathological conditions. The data indicate that targeting drebrin function could potentially be a preventive or therapeutic strategy for epilepsy treatment.

Transitions between neocortical seizure and non-seizure-like states and their association with presynaptic glutamate release

The transition between seizure and non-seizure states in neocortical epileptic networks is governed by distinct underlying dynamical processes. Based on the gamma distribution of seizure and inter-seizure durations, over time, seizures are highly likely to self-terminate; whereas, inter-seizure durations have a low chance of transitioning back into a seizure state. Yet, the chance of a state transition could be formed by multiple overlapping, unknown synaptic mechanisms. To identify the relationship between the underlying synaptic mechanisms and the chance of seizure-state transitions, we analyzed the skewed histograms of seizure durations in human intracranial EEG and seizure-like events (SLEs) in local field potential activity from mouse neocortical slices, using an objective method for seizure state classification. While seizures and SLE durations were demonstrated to have a unimodal distribution (gamma distribution shape parameter >1), suggesting a high likelihood of terminating, inter-SLE intervals were shown to have an asymptotic exponential distribution (gamma distribution shape parameter <1), suggesting lower probability of cessation. Then, to test cellular mechanisms for these distributions, we studied the modulation of synaptic neurotransmission during, and between, the in vitro SLEs. Using simultaneous local field potential and whole-cell voltage clamp recordings, we found a suppression of presynaptic glutamate release at SLE termination, as demonstrated by electrically- and optogenetically-evoked excitatory postsynaptic currents (EPSCs), and focal hypertonic sucrose application. Adenosine A1 receptor blockade interfered with the suppression of this release, changing the inter-SLE shape parameter from asymptotic exponential to unimodal, altering the chance of state transition occurrence with time. These findings reveal a critical role for presynaptic glutamate release in determining the chance of neocortical seizure state transitions.

The adenosine A1 receptor agonist WAG 994 suppresses acute kainic acid-induced status epilepticus in vivo

Status epilepticus (SE) is a neurological emergency characterized by continuous seizure activity lasting longer than 5 min, often with no recovery between seizures (Trinka et al., 2015). SE is refractory to benzodiazepine and second-line treatments in about 30% cases. Novel treatment approaches are urgently needed as refractory SE is associated with mortality rates of up to 70%. Robust adenosinergic anticonvulsant effects have been known for decades, but translation into seizure treatments was hampered by cardiovascular side effects. However, the selective adenosine A1 receptor agonist SDZ WAG 994 (WAG) displays diminished cardiovascular side effects compared to classic A1R agonists and was safely administered systemically in human clinical trials. Here, we investigate the anticonvulsant efficacy of WAG in vitro and in vivo. WAG robustly inhibited high-K⁺-induced continuous epileptiform activity in rat hippocampal slices (IC₅₀ = 52.5 nM). Importantly, WAG acutely suppressed SE in vivo induced by kainic acid (20 mg/kg i.p.) in mice. After SE was established, mice received three i.p. injections of WAG or diazepam (DIA, 5 mg/kg). Interestingly, DIA did not attenuate SE while the majority of WAG-treated mice (1 mg/kg) were seizure-free after three injections. Anticonvulsant effects were retained when a lower dose of WAG (0.3 mg/kg) was used. Importantly, all WAG-treated mice survived kainic acid induced SE. In summary, we report for the first time that an A1R agonist with an acceptable human side-effect profile can acutely suppress established SE in vivo. Our results suggest that WAG stops or vastly attenuates SE while DIA fails to mitigate SE in this model.

Medicinal Chemistry and Therapeutic Potential of Agonists, Antagonists and Allosteric Modulators of A1 Adenosine Receptor: Current Status and Perspectives

Adenosine is a purine nucleoside, responsible for the regulation of a wide range of physiological and pathophysiological conditions by binding with four G-protein-coupled receptors (GPCRs), namely A1, A2A, A2B and A3 adenosine receptors (ARs). In particular, A1 AR is ubiquitously present, mediating a variety of physiological processes throughout the body, thus represents a promising drug target for the management of various pathological conditions. Agonists of A1 AR are found to be useful for the treatment of atrial arrhythmia, angina, type-2 diabetes, glaucoma, neuropathic pain, epilepsy, depression and Huntington's disease, whereas antagonists are being investigated for the treatment of diuresis, congestive heart failure, asthma, COPD, anxiety and dementia. However, treatment with full A1 AR agonists has been associated with numerous challenges like cardiovascular side effects, off-target activation as well as desensitization of A1 AR leading to tachyphylaxis. In this regard, partial agonists of A1 AR have been found to be beneficial in enhancing insulin sensitivity and subsequently reducing blood glucose level, while avoiding severe CVS side effects and tachyphylaxis. Allosteric enhancer of A1 AR is found to be potent for the treatment of neuropathic pain, culminating the side effects related to off-target tissue activation of A1 AR. This review provides an overview of the medicinal chemistry and therapeutic potential of various agonists/partial agonists, antagonists and allosteric modulators of A1 AR, with a particular emphasis on their current status and future perspectives in clinical settings.

Activation of adenosine receptors modulates the efflux transporters in brain capillaries and restores the anticonvulsant effect of carbamazepine in carbamazepine resistant rats developed by window-pentylenetetrazole kindling

Up-regulation of efflux transporters in brain capillaries may lead to the decreased therapeutic efficacy of antiepileptic drugs in patients with Drug Resistant Epilepsy. Adenosine receptor activation in brain capillaries can modulate blood-brain barrier permeability by decreasing the protein levels and function of efflux transporters. Therefore, we aimed to investigate whether the activation of adenosine receptors improves convulsions outcome in carbamazepine (CBZ) resistant animals and modulates the protein levels of efflux transporters (P-GP, MRP1, MRP2) in brain capillaries. We employed the window-pentylenetetrazol (PTZ) kindling model to develop CBZ resistant rats by CBZ administration during the post-kindling phase, and tested if these animals displayed subsequent resistance to other antiepileptic drugs. Crucially, we investigated if the administration of a broad-spectrum adenosine agonist (NECA) improves convulsions control in CBZ resistant rats. Of potential therapeutic relevance, in CBZ resistant rats NECA restored the anticonvulsant effect of CBZ. We also evaluated how the resistance to CBZ and the activation of adenosine receptors with NECA affect protein levels of efflux transporters in brain capillaries, as quantified by western blot. While CBZ resistance was associated with the up-regulation of both P-GP/MRP2 in brain capillaries, with the administration of NECA in CBZ resistant rats, we observed a decrease of P-GP and an increase of MRP2 levels, in brain capillaries. Since the activation of adenosine receptors improves the outcome of convulsions probably through the modulation of the efflux transporters protein levels in brain capillaries, adenosine agonists could be useful as an adjunct therapy for the control of Drug Resistant Epilepsy.

Role of P2 receptors in normal brain development and in neurodevelopmental psychiatric disorders

The purinergic signaling system, including P2 receptors, plays an important role in various central nervous system (CNS) disorders. Over the last few decades, a substantial amount of accumulated data suggest that most P2 receptor subtypes (P2X1, 2, 3, 4, 6, and 7, and P2Y₁, ₂, ₆, ₁₂, and ₁₃) regulate neuronal/neuroglial developmental processes, such as proliferation, differentiation, migration of neuronal precursors, and neurite outgrowth. However, only a few of these subtypes (P2X2, P2X3, P2X4, P2X7, P2Y₁, and P2Y₂) have been investigated in the context of neurodevelopmental psychiatric disorders. The activation of these potential target receptors and their underlying mechanisms mainly influence the process of neuroinflammation. In particular, P2 receptor-mediated inflammatory cytokine release has been indicated to contribute to the complex mechanisms of a variety of CNS disorders. The released inflammatory cytokines could be utilized as biomarkers for neurodevelopmental and psychiatric disorders to improve the early diagnosis intervention, and prognosis. The population changes in gut microbiota after birth are closely linked to neurodevelopmental/neuropsychiatric disorders in later life; thus, the dynamic expression and function of P2 receptors on gut epithelial cells during disease processes indicate a novel avenue for the evaluation of disease progression and for the discovery of related therapeutic compounds.

Bioenergetic Mechanisms of Seizure Control

Epilepsy is characterized by the regular occurrence of seizures, which follow a stereotypical sequence of alterations in the electroencephalogram. Seizures are typically a self limiting phenomenon, concluding finally in the cessation of hypersynchronous activity and followed by a state of decreased neuronal excitability which might underlie the cognitive and psychological symptoms the patients experience in the wake of seizures. Many efforts have been devoted to understand how seizures spontaneously stop in hope to exploit this knowledge in anticonvulsant or neuroprotective therapies. Besides the alterations in ion-channels, transmitters and neuromodulators, the successive build up of disturbances in energy metabolism have been suggested as a mechanism for seizure termination. Energy metabolism and substrate supply of the brain are tightly regulated by different mechanisms called neurometabolic and neurovascular coupling. Here we summarize the current knowledge whether these mechanisms are sufficient to cover the energy demand of hypersynchronous activity and whether a mismatch between energy need and supply could contribute to seizure control.

In vitro Models for Seizure-Liability Testing Using Induced Pluripotent Stem Cells

The brain is the most complex organ in the body, controlling our highest functions, as well as regulating myriad processes which incorporate the entire physiological system. The effects of prospective therapeutic entities on the brain and central nervous system (CNS) may potentially cause significant injury, hence, CNS toxicity testing forms part of the “core battery” of safety pharmacology studies. Drug-induced seizure is a major reason for compound attrition during drug development. Currently, the rat ex vivo hippocampal slice assay is the standard option for seizure-liability studies, followed by primary rodent cultures. These models can respond to diverse agents and predict seizure outcome, yet controversy over the relevance, efficacy, and cost of these animal-based methods has led to interest in the development of human-derived models. Existing platforms often utilize rodents, and so lack human receptors and other drug targets, which may produce misleading data, with difficulties in inter-species extrapolation. Current electrophysiological approaches are typically used in a low-throughput capacity and network function may be overlooked. Human-derived induced pluripotent stem cells (iPSCs) are a promising avenue for neurotoxicity testing, increasingly utilized in drug screening and disease modeling. Furthermore, the combination of iPSC-derived models with functional techniques such as multi-electrode array (MEA) analysis can provide information on neuronal network function, with increased sensitivity to neurotoxic effects which disrupt different pathways. The use of an in vitro human iPSC-derived neural model for neurotoxicity studies, combined with high-throughput techniques such as MEA recordings, could be a suitable addition to existing pre-clinical seizure-liability testing strategies.

From Cultured Rodent Neurons to Human Brain Tissue: Model Systems for Pharmacological and Translational Neuroscience

To investigate the enormous complexity of the functional and pathological brain there are a number of possible experimental model systems to choose from. Depending on the research question choosing the appropriate model may not be a trivial task, and given the dynamic and intricate nature of an intact living brain several models might be needed to properly address certain questions. In this review, we aim to provide an overview of neural cell and tissue culture, reflecting on historic methodological milestones and providing a brief overview of the state-of-the-art. We additionally present an example of an effective model system pipeline, composed of dissociated mouse cultures, organotypics, acute mouse brain slices, and acute human brain slices, in that order. The sequential use of these four model systems allows a balance and progression from experimental control to human applicability, and provides a meta-model that can help validate basic research findings in a translational setting. We then conclude with a few remarks regarding the necessity of an integrated approach when performing translational and neuropharmacological studies.

Genome Editing in Neuroepithelial Stem Cells to Generate Human Neurons with High Adenosine-Releasing Capacity

As a powerful regulator of cellular homeostasis and metabolism, adenosine is involved in diverse neurological processes including pain, cognition, and memory. Altered adenosine homeostasis has also been associated with several diseases such as depression, schizophrenia, or epilepsy. Based on its protective properties, adenosine has been considered as a potential therapeutic agent for various brain disorders. Since systemic application of adenosine is hampered by serious side effects such as vasodilatation and cardiac suppression, recent studies aim at improving local delivery by depots, pumps, or cell-based applications. Here, we report on the characterization of adenosine-releasing human embryonic stem cell-derived neuroepithelial stem cells (long-term self-renewing neuroepithelial stem [lt-NES] cells) generated by zinc finger nuclease (ZFN)-mediated knockout of the adenosine kinase (ADK) gene. ADK-deficient lt-NES cells and their differentiated neuronal and astroglial progeny exhibit substantially elevated release of adenosine compared to control cells. Importantly, extensive adenosine release could be triggered by excitation of differentiated neuronal cultures, suggesting a potential activity-dependent regulation of adenosine supply. Thus, ZFN-modified neural stem cells might serve as a useful vehicle for the activity-dependent local therapeutic delivery of adenosine into the central nervous system. Stem Cells Translational Medicine 2018;7:477-486.

Attenuation of pentylenetrazole-induced acute status epilepticus in rats by adenosine involves inhibition of the mammalian target of rapamycin pathway

Adenosine (ADO) has been characterized as an endogenous anticonvulsant and alternative therapeutic drug, but its mechanism is not entirely clear. This study aimed to examine the relationship of ADO with the mammalian target of rapamycin (mTOR) in a Wistar rat model of pentylenetetrazole (PTZ)-induced acute status epilepticus. ADO (200 mg/kg) was administered intraperitoneally 30 min before PTZ (55-65 mg/kg) treatment, and Western blot assays and immunohistochemistry were performed 3 h after the onset of acute status epilepticus to detect phospho-TOR and the downstream target of mTOR, phospho-S6. The expression of these phosphoproteins in the hippocampus was significantly increased in PTZ-treated rats, but this increase was attenuated by the addition of ADO. To further verify a role for ADO in attenuating mTOR activity, we also evaluated its ability to suppress mTOR activity in normal rats that were not treated with PTZ. Our results suggest that ADO suppresses mTOR and S6 phosphorylation in normal rats and that this suppression can be reversed by the application of Compound C, an inhibitor of AMP-activated protein kinase, which functions as an upstream suppressor of the mTOR pathway. Thus, our results provide a novel antiepileptic mechanism for ADO in suppressing mTOR pathway activation upon PTZ-induced acute status epilepticus.

Prolonged life of human acute hippocampal slices from temporal lobe epilepsy surgery

Resected hippocampal tissue from patients with drug-resistant epilepsy presents a unique possibility to test novel treatment strategies directly in target tissue. The post-resection time for testing and analysis however is normally limited. Acute tissue slices allow for electrophysiological recordings typically up to 12 hours. To enable longer time to test novel treatment strategies such as, e.g., gene-therapy, we developed a method for keeping acute human brain slices viable over a longer period. Our protocol keeps neurons viable well up to 48 hours. Using a dual-flow chamber, which allows for microscopic visualisation of individual neurons with a submerged objective for whole-cell patch-clamp recordings, we report stable electrophysiological properties, such as action potential amplitude and threshold during this time. We also demonstrate that epileptiform activity, monitored by individual dentate granule whole-cell recordings, can be consistently induced in these slices, underlying the usefulness of this methodology for testing and/or validating novel treatment strategies for epilepsy.

Caffeine Controls Glutamatergic Synaptic Transmission and Pyramidal Neuron Excitability in Human Neocortex

Caffeine is the most widely used psychoactive drug, bolstering attention and normalizing mood and cognition, all functions involving cerebral cortical circuits. Whereas studies in rodents showed that caffeine acts through the antagonism of inhibitory A₁ adenosine receptors (A₁R), neither the role of A₁R nor the impact of caffeine on human cortical neurons is known. We here provide the first characterization of the impact of realistic concentrations of caffeine experienced by moderate coffee drinkers (50 μM) on excitability of pyramidal neurons and excitatory synaptic transmission in the human temporal cortex. Moderate concentrations of caffeine disinhibited several of the inhibitory A₁R-mediated effects of adenosine, similar to previous observations in the rodent brain. Thus, caffeine restored the adenosine-induced decrease of both intrinsic membrane excitability and excitatory synaptic transmission in the human pyramidal neurons through antagonism of post-synaptic A₁R. Indeed, the A₁R-mediated effects of endogenous adenosine were more efficient to inhibit synaptic transmission than neuronal excitability. This was associated with a distinct affinity of caffeine for synaptic versus extra-synaptic human cortical A₁R, probably resulting from a different molecular organization of A₁R in human cortical synapses. These findings constitute the first neurophysiological description of the impact of caffeine on pyramidal neuron excitability and excitatory synaptic transmission in the human temporal cortex, providing adequate ground for the effects of caffeine on cognition in humans.

Contribution of Intrinsic Lactate to Maintenance of Seizure Activity in Neocortical Slices from Patients with Temporal Lobe Epilepsy and in Rat Entorhinal Cortex

Neuronal lactate uptake supports energy metabolism associated with synaptic signaling and recovery of extracellular ion gradients following neuronal activation. Altered expression of the monocarboxylate transporters (MCT) in temporal lobe epilepsy (TLE) hampers lactate removal into the bloodstream. The resulting increase in parenchymal lactate levels might exert both, anti- and pro-ictogen effects, by causing acidosis and by supplementing energy metabolism, respectively. Hence, we assessed the contribution of lactate to the maintenance of transmembrane potassium gradients, synaptic signaling and pathological network activity in chronic epileptic human tissue. Stimulus induced and spontaneous field potentials and extracellular potassium concentration changes (∆[K⁺]_O) were recorded in parallel with tissue pO₂ and pH in slices from TLE patients while blocking MCTs by α-cyano-4-hydroxycinnamic acid (4-CIN) or d-lactate. Intrinsic lactate contributed to the oxidative energy metabolism in chronic epileptic tissue as revealed by the changes in pO₂ following blockade of lactate uptake. However, unlike the results in rat hippocampus, ∆[K⁺]_O recovery kinetics and field potential amplitude did not depend on the presence of lactate. Remarkably, inhibition of lactate uptake exerted pH-independent anti-seizure effects both in healthy rat and chronic epileptic tissue and this effect was partly mediated via adenosine 1 receptor activation following decreased oxidative metabolism.