Grafts of adenosine-releasing cells suppress seizures in kindling epilepsy

Vector-Mediated Delivery of Transgenes and RNA Interference-Based Gene Silencing Sequences to Astrocytes for Disease Management: Advances and Prospectives

Astrocytes are a type of important glial cell in the brain that serve crucial functions in regulating neuronal activity, facilitating communication between neurons, and keeping everything in balance. In this abstract, we explore current methods and future approaches for using vectors to precisely target astrocytes in the fight against various illnesses. In order to deliver therapeutic cargo selectively to astrocytes, researchers have made tremendous progress by using viral vectors such as adeno-associated viruses (AAVs) and lentiviruses. It has been established that engineered viral vectors are capable of either crossing the blood-brain barrier (BBB) or being delivered intranasally, which facilitates their entrance into the brain parenchyma. These vectors are able to contain transgenes that code for neuroprotective factors, synaptic modulators, or anti-inflammatory medicines, which pave the way for multiple approaches to disease intervention. Strategies based on RNA interference (RNAi) make vector-mediated astrocyte targeting much more likely to work. Small interfering RNAs (siRNAs) and short hairpin RNAs (shRNAs) are two types of RNA that can be made to silence disease-related genes in astrocytes. Vector-mediated delivery in conjunction with RNAi techniques provides a powerful toolkit for investigating the complex biological pathways that contribute to disease development. However, there are still a number of obstacles to overcome in order to perfect the specificity, safety, and duration of vector-mediated astrocyte targeting. In order to successfully translate research findings into clinical practise, it is essential to minimise off-target effects and the risk of immunogenicity. To demonstrate the therapeutic effectiveness of these strategies, rigorous preclinical investigation and validation are required.

Anticonvulsant Profile of Selected Medium-Chain Fatty Acids (MCFAs) Co-Administered with Metformin in Mice in Acute and Chronic Treatment

In contrast to the other components of the medium-chain triglycerides ketogenic diet (MCT KD), i.e., caprylic acid (CA8), a comprehensive evaluation of caproic (CA6) and lauric acids' (CA12) properties in standard chemical and electrical seizure tests in mice has not yet been performed. We investigated their effects in maximal electroshock seizure threshold (MEST), 6 Hz seizure threshold and intravenous (i.v.) pentylenetetrazole (PTZ) seizure tests. Since ketone body production can be regulated by the activation of 5'AMP-activated protein kinase (AMPK), we hypothesized that metformin (an AMPK activator) enhance ketogenesis and would act synergistically with the fatty acids to inhibit convulsions. We assessed the effects of acute and chronic co-treatment with metformin and CA6/CA8 on seizures. CA6 and CA12 (p.o.) increased seizure threshold in the 6 Hz seizure test. CA6 at the highest tested dose (30 mmol/kg) developed toxicity in several mice, impaired motor performance and induced ketoacidosis. Acute and chronic co-treatment with metformin and CA6/CA8 did not affect seizure thresholds. Moreover, we observed the pro-convulsive effect of the acute co-administration of CA8 (5 mmol/kg) and metformin (100 mg/kg). Since this co-treatment was pro-convulsive, the safety profile and risk/benefit ratio of MCT KD and metformin concomitant therapy in epileptic patients should be further evaluated.

Overview Article Astrocytes as Initiators of Epilepsy

Astrocytes play a dual role in the brain. On the one hand, they are active signaling partners of neurons and can for instance control synaptic transmission and its plasticity. On the other hand, they fulfill various homeostatic functions such as clearance of glutamate and K⁺ released from neurons. The latter is for instance important for limiting neuronal excitability. Therefore, an impairment or failure of glutamate and K⁺ clearance will lead to increased neuronal excitability, which could trigger or aggravate brain diseases such as epilepsy, in which neuronal hyperexcitability plays a role. Experimental data indicate that astrocytes could have such a causal role in epilepsy, but the role of astrocytes as initiators of epilepsy and the relevant mechanisms are under debate. In this overview, we will discuss the potential mechanisms with focus on K⁺ clearance, glutamate uptake and homoeostasis and related mechanisms, and the evidence for their causative role in epilepsy.

Therapeutic Potential of Mesenchymal Stem Cells in the Treatment of Epilepsy and Their Interaction with Antiseizure Medications

Epilepsy is a life-threatening neurological disease that affects approximately 70 million people worldwide. Although the vast majority of patients may be successfully managed with currently used antiseizure medication (ASM), the search for alternative therapies is still necessary due to pharmacoresistance in about 30% of patients with epilepsy. Here, we review the effects of ASMs on stem cell treatment when they could be, as expected, co-administered. Indeed, it has been reported that ASMs produce significant effects on the differentiation and determination of stem cell fate. In addition, we discuss more recent findings on mesenchymal stem cells (MSCs) in pre-clinical and clinical investigations. In this regard, their ability to differentiate into various cell types, reach damaged tissues and produce and release biologically active molecules with immunomodulatory/anti-inflammatory and regenerative properties make them a high-potential therapeutic tool to address neuroinflammation in different neurological disorders, including epilepsy. Overall, the characteristics of MSCs to be genetically engineered, in order to replace dysfunctional elements with the aim of restoring normal tissue functioning, suggested that these cells could be good candidates for the treatment of epilepsy refractory to ASMs. Further research is required to understand the potential of stem cell treatment in epileptic patients and its interaction with ASMs.

Deep brain stimulation of the anterior thalamus attenuates PTZ kindling with concomitant reduction of adenosine kinase expression in rats

BACKGROUND

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is an emerging therapy to provide seizure control in patients with refractory epilepsy, although its therapeutic mechanisms remain elusive.

OBJECTIVE

We tested the hypothesis that ANT-DBS might interfere with the kindling process using three experimental groups: PTZ, DBS-ON and DBS-OFF.

METHODS

79 male rats were used in two experiments and exposed to chemical kindling with pentylenetetrazole (PTZ, 30 mg/kg i.p.), delivered three times a week for a total of 18 kindling days (KD). These animals were divided into two sets of three groups: PTZ (n = 26), DBS-ON (n = 28) and DBS-OFF (n = 25). ANT-DBS (130 Hz, 90 μs, and 200 μA) was paired with PTZ injections, while DBS-OFF group, although implanted remained unstimulated. After KD 18, the first set of PTZ-treated animals and an additional group of 11 naïve rats were euthanized for brain extraction to study adenosine kinase (ADK) expression. To observe possible long-lasting effects of ANT stimulation, the second set of animals underwent a 1-week treatment and stimulation-free period after KD 18 before a final PTZ challenge.

RESULTS

ANT-DBS markedly attenuated kindling progression in the DBS-ON group, which developed seizure scores of 2.4 on KD 13, whereas equivalent seizure scores were reached in the DBS-OFF and PTZ groups as early as KD5 and KD6, respectively. The incidence of animals with generalized seizures following 3 consecutive PTZ injections was 94%, 74% and 21% in PTZ, DBS-OFF and DBS-ON groups, respectively. Seizure scores triggered by a PTZ challenge one week after cessation of stimulation revealed lasting suppression of seizure scores in the DBS-ON group (2.7 ± 0.2) compared to scores of 4.5 ± 0.1 for the PTZ group and 4.3 ± 0.1 for the DBS-OFF group (P = 0.0001). While ANT-DBS protected hippocampal cells, the expression of ADK was decreased in the DBS-ON group compared to both PTZ (P < 0.01) and naïve animals (P < 0.01).

CONCLUSIONS

Our study demonstrates that ANT-DBS interferes with the kindling process and reduced seizure activity was maintained after a stimulation free period of one week. Our findings suggest that ANT-DBS might have additional therapeutic benefits to attenuate seizure progression in epilepsy.

Caffeine excites medial parabrachial nucleus neurons of mice by blocking adenosine A1 receptor

Caffeine has been used as a first-line drug for treatment of apnea neonatorum for decades due to its high safety and effectiveness. Studies report that caffeine mainly acts as a blocker of Adenosine Receptors (ARs). However, the mechanism of caffeine in reducing apnea neonatorum in the central nervous system has not been fully explored. Medial parabrachial nucleus (MPB) is part of the respiratory center of the pons that may be related to the activity of caffeine. Previous studies have not explored the effect and mechanism of caffeine on MPB neurons. To elucidate this, the current study used antagonists of A1 and A2a receptors to mimic the effect of caffeine in MPB of mice in vitro using the patch-clamp technique. The firing rates and spontaneous post-synaptic currents were recorded. The findings of the study showed that caffeine excited MPB neurons. Notably, the adenosine A1R antagonist 8-cyclopentyl-1,3-dimethyl-xanthine (CPT) but not the adenosine A2aR antagonist Istradefylline (KW6002) mimicked the exciting effect of caffeine, implying that caffeine excited MPB neurons in mice by blocking A1Rs. Further, the results indicated that caffeine could increase efficiency of synaptic transmission to excite MPB neurons. These findings suggest that A1Rs in MPB may be potential targets for caffeine in reducing apnea neonatorum.

Optogenetic stimulus-triggered acquisition of seizure resistance

Unlike an electrical circuit, the hardware of the brain is susceptible to change. Repeated electrical brain stimulation mimics epileptogenesis. After such "kindling" process, a moderate stimulus would become sufficient in triggering a severe seizure. Here, we report that optogenetic neuronal stimulation can also convert the rat brain to a hyperexcitable state. However, continued stimulation once again converted the brain to a state that was strongly resistant to seizure induction. Histochemical examinations showed that moderate astrocyte activation was coincident with resilience acquisition. Administration of an adenosine A1 receptor antagonist instantly reverted the brain back to a hyperexcitable state, suggesting that hyperexcitability was suppressed by adenosine. Furthermore, an increase in basal adenosine was confirmed using in vivo microdialysis. Daily neuron-to-astrocyte signaling likely prompted a homeostatic increase in the endogenous actions of adenosine. Our data suggest that a certain stimulation paradigm could convert the brain circuit resilient to epilepsy without exogenous drug administration.

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.

Targeting Adenosine Receptors in Neurological Diseases

Adenosine plays a significant role in neurotransmission process by controlling the blood pressure, while adenosine triphosphate (ATP) acts as a neuromodulator and neurotransmitter and by activation of P2 receptors, regulates the contractility of the heart. Adenosine signaling is essential in the process of regeneration by regulating proliferation, differentiation, and apoptosis of stem cells. In this review, we have selected neurological disorders (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and epilepsy) with clinical trials using antagonists and epigenetic tools targeting adenosine receptor as a therapeutic approach in the treatment of these disorders. Promising results have been reported from many clinical trials. It has been found that higher expression levels of A2A and P2X7 receptors in neurological disorders further complicate the disease condition. Therefore, modulations of these receptors by using antagonists of these receptors or SAM (S-adenosylmethionine) therapy as an epigenetic tool could be useful in reversing the complications of these disorders. Finally, we suggest that modulation of adenosine receptors in neurological disorders can increase the regenerative phase by increasing the rate of proliferation and differentiation in the damaged tissues.

Astrocytes and Epilepsy

Changes in astrocyte channels, transporters, and metabolism play a critical role in seizure generation and epilepsy. In particular, alterations in astrocyte potassium, glutamate, water and adenosine homeostasis and gap junctional coupling have all been associated with hyperexcitability and epileptogenesis (largely in temporal lobe epilepsy). Distinct astrocytic changes have also been identified in other types of epilepsy, such as tuberous sclerosis, tumor-associated epilepsy and post-traumatic epilepsy. Together, the emerging literature on astrocytes and epilepsy provides powerful rationale for distinct new therapeutic targets that are astrocyte-specific.

Adenosine kinase: A key regulator of purinergic physiology

Adenosine (ADO) is an essential biomolecule for life that provides critical regulation of energy utilization and homeostasis. Adenosine kinase (ADK) is an evolutionary ancient ribokinase derived from bacterial sugar kinases that is widely expressed in all forms of life, tissues and organ systems that tightly regulates intracellular and extracellular ADO concentrations. The facile ability of ADK to alter ADO availability provides a "site and event" specificity to the endogenous protective effects of ADO in situations of cellular stress. In addition to modulating the ability of ADO to activate its cognate receptors (P1 receptors), nuclear ADK isoform activity has been linked to epigenetic mechanisms based on transmethylation pathways. Previous drug discovery research has targeted ADK inhibition as a therapeutic approach to manage epilepsy, pain, and inflammation. These efforts generated multiple classes of highly potent and selective inhibitors. However, clinical development of early ADK inhibitors was stopped due to apparent mechanistic toxicity and the lack of suitable translational markers. New insights regarding the potential role of the nuclear ADK isoform (ADK-Long) in the epigenetic modulation of maladaptive DNA methylation offers the possibility of identifying novel ADK-isoform selective inhibitors and new interventional strategies that are independent of ADO receptor activation.

Diadenosine-Polyphosphate Analogue AppCH2ppA Suppresses Seizures by Enhancing Adenosine Signaling in the Cortex

Epilepsy is a multifactorial disorder associated with neuronal hyperexcitability that affects more than 1% of the human population. It has long been known that adenosine can reduce seizure generation in animal models of epilepsies. However, in addition to various side effects, the instability of adenosine has precluded its use as an anticonvulsant treatment. Here we report that a stable analogue of diadenosine-tetraphosphate: AppCH2ppA effectively suppresses spontaneous epileptiform activity in vitro and in vivo in a Tuberous Sclerosis Complex (TSC) mouse model (Tsc1+/-), and in postsurgery cortical samples from TSC human patients. These effects are mediated by enhanced adenosine signaling in the cortex post local neuronal adenosine release. The released adenosine induces A1 receptor-dependent activation of potassium channels thereby reducing neuronal excitability, temporal summation, and hypersynchronicity. AppCH2ppA does not cause any disturbances of the main vital autonomous functions of Tsc1+/- mice in vivo. Therefore, we propose this compound to be a potent new candidate for adenosine-related treatment strategies to suppress intractable epilepsies.

Role of Adenosine in Epilepsy and Seizures

Adenosine is an endogenous anticonvulsant and neuroprotectant of the brain. Seizure activity produces large quantities of adenosine, and it is this seizure-induced adenosine surge that normally stops a seizure. However, within the context of epilepsy, adenosine plays a wide spectrum of different roles. It not only controls seizures (ictogenesis), but also plays a major role in processes that turn a normal brain into an epileptic brain (epileptogenesis). It is involved in the control of abnormal synaptic plasticity and neurodegeneration and plays a major role in the expression of comorbid symptoms and complications of epilepsy, such as sudden unexpected death in epilepsy (SUDEP). Given the important role of adenosine in epilepsy, therapeutic strategies are in development with the goal to utilize adenosine augmentation not only for the suppression of seizures but also for disease modification and epilepsy prevention, as well as strategies to block adenosine A_2A receptor overfunction associated with neurodegeneration. This review provides a comprehensive overview of the role of adenosine in epilepsy.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

The role of adenosine in epilepsy

Adenosine is a well-characterized endogenous anticonvulsant and seizure terminator of the brain. Through a combination of adenosine receptor-dependent and -independent mechanisms, adenosine affects seizure generation (ictogenesis), as well as the development of epilepsy and its progression (epileptogenesis). Maladaptive changes in adenosine metabolism, in particular increased expression of the astroglial enzyme adenosine kinase (ADK), play a major role in epileptogenesis. Increased expression of ADK has dual roles in both reducing the inhibitory tone of adenosine in the brain, which consequently reduces the threshold for seizure generation, and also driving an increased flux of methyl-groups through the transmethylation pathway, thereby increasing global DNA methylation. Through these mechanisms, adenosine is uniquely positioned to link metabolism with epigenetic outcome. Therapeutic adenosine augmentation therefore not only holds promise for the suppression of seizures in epilepsy, but moreover the prevention of epilepsy and its progression overall. This review will focus on adenosine-related mechanisms implicated in ictogenesis and epileptogenesis and will discuss therapeutic opportunities and challenges.

Adenosine A1 Receptor Agonist 2-chloro-N6-cyclopentyladenosine and Hippocampal Excitability During Brain Development in Rats

Objective: The adenosinergic system may influence excitability in the brain. Endogenous and exogenous adenosine has anticonvulsant activity presumably by activating A1 receptors. Adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) may thus bolster anticonvulsant effects, but its action and the number of A1 receptors at different developmental stages are not known.

Methods: Hippocampal epileptic afterdischarges (ADs) were elicited in 12-, 15-, 18-, 25-, 45-, and 60-day-old rats. Stimulation and recording electrodes were implanted into the dorsal hippocampus. The A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 0.5 or 1 mg/kg) was administered intraperitoneally 10 min before the first stimulation. Control animals were injected with saline. All rats were stimulated with a 2-s series of 1-ms biphasic pulses delivered at 60 Hz with increasing stepwise intensity (0.05–0.6 mA). Each age and dose group contained 9–14 animals. The AD thresholds and durations were evaluated, and the A1 receptors were detected in the hippocampus in 7-, 10-, 12-, 15-, 18-, 21-, 25-, 32-, and 52-day-old rats.

Results: Both CCPA doses significantly increased hippocampal AD thresholds in 12-, 15-, 18-, and 60-day-old rats compared to controls. In contrast, the higher dose significantly decreased AD threshold in the 25-day-old rats. The AD durations were significantly shortened in all age groups except for 25-day-old rats where they were significantly prolonged. A1 receptor expression in the hippocampus was highest in 10-day-old rats and subsequently decreased.

Significance: The adenosine A1 receptor agonist CCPA exhibited anticonvulsant activity at all developmental stages studied here except for 25-day-old rats. Age-related differences might be due to the development of presynaptic A1 receptors in the hippocampus.

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.

Nitrobenzylthioinosine mimics adenosine to attenuate the epileptiform discharge of hippocampal neurons from epileptic rats

Nitrobenzylthioinosine (NBTI), a specific inhibitor of type 1 equilibrative nucleoside transporter, could regulate the extracellular adenosine concentration and have protective roles in seizures. However, the protection mechanism of NBTI in seizures remains poorly understood. Here, the expression pattern and subcellular distribution of adenosine A1 receptor were detected by Western blot analysis and double-labeling immunofluorescence staining in Lithium Chloride-Pilocarpine induced epileptic rat model. At 24 h after pilocarpine induced rat seizures, hippocampal slices were prepared and the evoked excitatory postsynaptic currents (eEPSCs) amplitude of pyramidal neurons in hippocampus CA1 region was recorded using whole-cell patch clamp. In vivo, compared to control group, Western blotting analysis showed that the expression of adenosine A1 receptor protein was increased at 24 h and 72 h after seizure, didn't change at 0 min and 1 w, and decreased at 2 w. Double-label immunofluorescence revealed that adenosine A1 receptor was mainly expressed in the membrane and cytoplasm of neurons. In Vitro, adenosine decreased the eEPSCs amplitude of pyramidal neurons in hippocampus CA1 region, NBTI also had the same effect. Meantime, NBTI could further inhibit eEPSCs amplitude on the basis of lower concentration adenosine (50μM), and adenosine A1 receptor inhibitor DPCPX partially reversed this effect. Taken together, we confirmed that the expression of adenosine A1 receptor protein was increased in the early seizures and decreased in the late seizures. At the same time, NBTI mimics adenosine to attenuate the epileptiform discharge through adenosine A1 receptor, which might provide a novel therapeutic approach toward the control of epilepsy.

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.

Equilibrative nucleoside transporters-A review

Equilibrative nucleoside transporters (ENTs) are polytopic integral membrane proteins that mediate the transport of nucleosides, nucleobases, and therapeutic analogs. The best-characterized ENTs are the human transporters hENT1 and hENT2. However, non-mammalian eukaryotic ENTs have also been studied (e.g., yeast, parasitic protozoa). ENTs are major pharmaceutical targets responsible for modulating the efficacy of more than 30 approved drugs. However, the molecular mechanisms and chemical determinants of ENT-mediated substrate recognition, binding, inhibition, and transport are poorly understood. This review highlights findings on the characterization of ENTs by surveying studies on genetics, permeant and inhibitor interactions, mutagenesis, and structural models of ENT function.

Adenosine and Epilepsy: From Therapeutic Rationale to New Therapeutic Strategies

Adenosine, as the brain’s endogenous anticonvulsant, is considered to be responsible for seizure arrest and postictal refractoriness. On the other hand, deficiencies within the adenosine-based neuromodulatory system may contribute to epileptogenesis. Based on these natural mechanisms and on findings that adenosine and its analogs can suppress pharmacoresistant seizures, a new field of adenosine-based therapies has emerged, including the use of adenosine receptor agonists and adenosine transport inhibitors, or the inhibition of adenosine kinase, which is thought to be the key enzyme for the regulation of intra- and extracellular adenosine levels. However, most of these pharmacological approaches are limited by strong systemic side effects ranging from a decrease of heart rate, blood pressure, and body temperature to sedation. Recently, new strategies have been developed aimed at the local reconstitution of the inhibitory adenosinergic tone by intracerebral implantation of cells engineered to release adenosine. Adenosine-releasing cells or devices implanted into or near a seizure focus offer new hopes for a side effect-free therapy for pharmacoresistant epilepsy.

Purinergic signaling in epilepsy

Until recently, analysis of the mechanisms underlying epilepsy was centered on neuron dysfunctions. Accordingly, most of the available pharmacological treatments aim at reducing neuronal excitation or at potentiating neuronal inhibition. These therapeutic options can lead to obvious secondary effects, and, moreover, seizures cannot be controlled by any known medication in one-third of the patients. A purely neurocentric view of brain functions and dysfunctions has been seriously questioned during the past 2 decades because of the accumulation of experimental data showing the functional importance of reciprocal interactions between glial cells and neurons. In the case of epilepsy, our current knowledge of the human disease and analysis of animal models clearly favor the involvement of astrocytes and microglial cells during the progression of the disease, including at very early stages, opening the way to the identification of new therapeutic targets. Purinergic signaling is a fundamental feature of neuron-glia interactions, and increasing evidence indicates that modifications of this pathway contribute to the functional remodeling of the epileptic brain. This Review discusses the recent experimental results indicating the roles of astrocytic and microglial P2X and P2Y receptors in epilepsy. © 2016 Wiley Periodicals, Inc.

The Biochemistry and Epigenetics of Epilepsy: Focus on Adenosine and Glycine

Epilepsy, one of the most prevalent neurological conditions, presents as a complex disorder of network homeostasis characterized by spontaneous non-provoked seizures and associated comorbidities. Currently used antiepileptic drugs have been designed to suppress neuronal hyperexcitability and thereby to suppress epileptic seizures. However, the current armamentarium of antiepileptic drugs is not effective in over 30% of patients, does not affect the comorbidities of epilepsy, and does not prevent the development and progression of epilepsy (epileptogenesis). Prevention of epilepsy and its progression remains the Holy Grail for epilepsy research and therapy development, requiring novel conceptual advances to find a solution to this urgent medical need. The methylation hypothesis of epileptogenesis suggests that changes in DNA methylation are implicated in the progression of the disease. In particular, global DNA hypermethylation appears to be associated with chronic epilepsy. Clinical as well as experimental evidence demonstrates that epilepsy and its progression can be prevented by biochemical manipulations and those that target previously unrecognized epigenetic functions contributing to epilepsy development and maintenance of the epileptic state. This mini-review will discuss, epigenetic mechanisms implicated in epileptogenesis and biochemical interactions between adenosine and glycine as a conceptual advance to understand the contribution of maladaptive changes in biochemistry as a major contributing factor to the development of epilepsy. New findings based on biochemical manipulation of the DNA methylome suggest that: (i) epigenetic mechanisms play a functional role in epileptogenesis; and (ii) therapeutic reconstruction of the epigenome is an effective antiepileptogenic therapy.

Comorbidities in Neurology: Is adenosine the common link?

Comorbidities in Neurology represent a major conceptual and therapeutic challenge. For example, temporal lobe epilepsy (TLE) is a syndrome comprised of epileptic seizures and comorbid symptoms including memory and psychiatric impairment, depression, and sleep dysfunction. Similarly, Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic Lateral Sclerosis (ALS) are accompanied by various degrees of memory dysfunction. Patients with AD have an increased likelihood for seizures, whereas all four conditions share certain aspects of psychosis, depression, and sleep dysfunction. This remarkable overlap suggests common pathophysiological mechanisms, which include synaptic dysfunction and synaptotoxicity, as well as glial activation and astrogliosis. Astrogliosis is linked to synapse function via the tripartite synapse, but astrocytes also control the availability of gliotransmitters and adenosine. Here we will specifically focus on the 'adenosine hypothesis of comorbidities' implying that astrocyte activation, via overexpression of adenosine kinase (ADK), induces a deficiency in the homeostatic tone of adenosine. We present evidence from patient-derived samples showing astrogliosis and overexpression of ADK as common pathological hallmark of epilepsy, AD, PD, and ALS. We discuss a transgenic 'comorbidity model', in which brain-wide overexpression of ADK and resulting adenosine deficiency produces a comorbid spectrum of seizures, altered dopaminergic function, attentional impairment, and deficits in cognitive domains and sleep regulation. We conclude that dysfunction of adenosine signaling is common in neurological conditions, that adenosine dysfunction can explain co-morbid phenotypes, and that therapeutic adenosine augmentation might be effective for the treatment of comorbid symptoms in multiple neurological conditions.

Adenosine deaminase and adenosine kinase expression in human glioma and their correlation with glioma‑associated epilepsy

The aim of the present study was to investigate adenosine deaminase (ADA) and adenosine kinase (ADK) expression in human glioma and to explore its correlation with glioma-associated epilepsy. Tumor tissues (n=45) and peritumoral tissues (n=14) were obtained from glioma patients undergoing surgery. Normal control tissues (n=8) were obtained from brain trauma patients. The disease grade was determined by histological evaluation and the degree of tumor invasion was evaluated using immunofluorescence analyses. mRNA and protein expression of ADA and ADK were evaluated using reverse transcription quantitative polymerase chain reaction or western blot analysis, respectively. Based on histological evaluations, four cases were classified as Grade I gliomas, 18 cases as Grade II, 17 cases as Grade III and six cases were considered Grade IV. Increased ADA and ADK expression was observed in tumor tissues. ADA was predominantly distributed in the cytoplasm of tumor cells, whereas ADK was detected in the cytoplasm as well as in the nuclei. ADA and ADK levels were upregulated in patients with Grade II and Grade III gliomas compared to those in control subjects (p<0.05). In addition, tumor invasion was detected in peritumoral tissues. The number of ADA-positive or ADK-positive cells in tumor tissues was similar between glioma patients with and without epilepsy (p>0.05). However, ADA and ADK expression was upregulated in peritumoral tissues derived from patients with epilepsy compared to that in glioma patients without epilepsy. The results of the present study suggested that ADA and ADK are involved in glioma progression, and that increased ADA and ADK levels in peritumoral tissues may be associated with epilepsy in glioma patients.

Adenosinergic signaling in epilepsy

Despite the introduction of at least 20 new antiepileptic drugs (AEDs) into clinical practice over the past decades, about one third of all epilepsies remain refractory to conventional forms of treatment. In addition, currently used AEDs have been developed to suppress neuronal hyperexcitability, but not necessarily to address pathogenic mechanisms involved in epilepsy development or progression (epileptogenesis). For those reasons endogenous seizure control mechanisms of the brain may provide alternative therapeutic opportunities. Adenosine is a well characterized endogenous anticonvulsant and seizure terminator of the brain. Several lines of evidence suggest that endogenous adenosine-mediated seizure control mechanisms fail in chronic epilepsy, whereas therapeutic adenosine augmentation effectively prevents epileptic seizures, even those that are refractory to conventional AEDs. New findings demonstrate that dysregulation of adenosinergic mechanisms are intricately involved in the development of epilepsy and its comorbidities, whereas adenosine-associated epigenetic mechanisms may play a role in epileptogenesis. The first goal of this review is to discuss how maladaptive changes of adenosinergic mechanisms contribute to the expression of seizures (ictogenesis) and the development of epilepsy (epileptogenesis) by focusing on pharmacological (adenosine receptor dependent) and biochemical (adenosine receptor independent) mechanisms as well as on enzymatic and transport based mechanisms that control the availability (homeostasis) of adenosine. The second goal of this review is to highlight innovative adenosine-based opportunities for therapeutic intervention aimed at reconstructing normal adenosine function and signaling for improved seizure control in chronic epilepsy. New findings suggest that transient adenosine augmentation can have lasting epigenetic effects with disease modifying and antiepileptogenic outcome. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Ketogenic diet prevents epileptogenesis and disease progression in adult mice and rats

Epilepsy is a highly prevalent seizure disorder which tends to progress in severity and become refractory to treatment. Yet no therapy is proven to halt disease progression or to prevent the development of epilepsy. Because a high fat low carbohydrate ketogenic diet (KD) augments adenosine signaling in the brain and because adenosine not only suppresses seizures but also affects epileptogenesis, we hypothesized that a ketogenic diet might prevent epileptogenesis through similar mechanisms. Here, we tested this hypothesis in two independent rodent models of epileptogenesis. Using a pentylenetetrazole kindling paradigm in mice, we first show that a KD, but not a conventional antiepileptic drug (valproic acid), suppressed kindling-epileptogenesis. Importantly, after treatment reversal, increased seizure thresholds were maintained in those animals kindled in the presence of a KD, but not in those kindled in the presence of valproic acid. Next, we tested whether a KD can halt disease progression in a clinically relevant model of progressive epilepsy. Epileptic rats that developed spontaneous recurrent seizures after a pilocarpine-induced status epilepticus were treated with a KD or control diet (CD). Whereas seizures progressed in severity and frequency in the CD-fed animals, KD-fed animals showed a prolonged reduction of seizures, which persisted after diet reversal. KD-treatment was associated with increased adenosine and decreased DNA methylation, the latter being maintained after diet discontinuation. Our findings demonstrate that a KD prevented disease progression in two mechanistically different models of epilepsy, and suggest an epigenetic mechanism underlying the therapeutic effects.

Adenosine 2A receptors in acute kidney injury

Acute kidney injury (AKI) is an important clinical problem that may lead to death and for those who survive, the sequelae of AKI include loss of quality of life, chronic kidney disease and end-stage renal disease. The incidence of AKI continues to rise without clear successes in humans for the pharmacological prevention of AKI or treatment of established AKI. Dendritic cells and macrophages are critical early initiators of innate immunity in the kidney and orchestrate inflammation subsequent to ischaemia-reperfusion injury. These innate cells are the most abundant leucocytes present in the kidney, and they represent a heterogeneous population of cells that are capable of responding to cues from the microenvironment derived from pathogens or endogenous inflammatory mediators such as cytokines or anti-inflammatory mediators such as adenosine. Lymphocyte subsets such as natural killer T cells and Tregs also play roles in regulating ischaemic injury by promoting and suppressing inflammation respectively. Adenosine, produced in response to IR, is generally considered as a protective signalling molecule and elicits its physiological responses through four distinct adenosine receptors. However, its short half-life, lack of specificity and rapid metabolism limit the use of adenosine as a therapeutic agent. These adenosine receptors play various roles in regulating the activity of the aforementioned hematopoietic cells in elevated levels of adenosine such as during hypoxia. This review focuses on the importance of one receptor, the adenosine 2A subtype, in blocking inflammation associated with AKI.

Regenerative therapy for hippocampal degenerative diseases: lessons from preclinical studies

Increase in life expectancy has put neurodegenerative diseases on the rise. Amongst these, degenerative diseases involving hippocampus like Alzheimer's disease (AD) and temporal lobe epilepsy (TLE) are ranked higher as it is vulnerable to excitotoxicity induced neuronal dysfunction and death resulting in cognitive impairment. Modern medicines have not succeeded in halting the progression of these diseases rendering them incurable and often fatal. Under such scenario, regenerative studies employing stem cells or their by-products in animal models of AD and TLE have yielded encourageing results. This review focuses on the distinct cell types, such as hippocampal cell lines, neural precursor cells, embryonic stem cells derived neural precursor cells, induced pluripotent stem cells, induced neurons and mesenchymal stem cells, which can be employed to rescue hippocampal functions in neurodegenerative diseases like AD and TLE. Besides, the divergent mechanisms through which cell based therapy confer neuroprotection, current impediments and possible improvements in stem cell transplantation strategies are discussed. Authors are aware of the voluminous literature available on this issue and have made a sincere attempt to put forth the current status of research in the field of cell based therapy concurrently discussing the promise it holds for combating neurodegenerative diseases like AD and TLE in the near future. Copyright © 2015 John Wiley & Sons, Ltd.

Adenosine receptor neurobiology: overview

Adenosine is a naturally occurring nucleoside that is distributed ubiquitously throughout the body as a metabolic intermediary. In the brain, adenosine functions as an important upstream neuromodulator of a broad spectrum of neurotransmitters, receptors, and signaling pathways. By acting through four G-protein-coupled receptors, adenosine contributes critically to homeostasis and neuromodulatory control of a variety of normal and abnormal brain functions, ranging from synaptic plasticity, to cognition, to sleep, to motor activity to neuroinflammation, and cell death. This review begun with an overview of the gene and genome structure and the expression pattern of adenosine receptors (ARs). We feature several new developments over the past decade in our understanding of AR functions in the brain, with special focus on the identification and characterization of canonical and noncanonical signaling pathways of ARs. We provide an update on functional insights from complementary genetic-knockout and pharmacological studies on the AR control of various brain functions. We also highlight several novel and recent developments of AR neurobiology, including (i) recent breakthrough in high resolution of three-dimension structure of adenosine A2A receptors (A2ARs) in several functional status, (ii) receptor-receptor heterodimerization, (iii) AR function in glial cells, and (iv) the druggability of AR. We concluded the review with the contention that these new developments extend and strengthen the support for A1 and A2ARs in brain as therapeutic targets for neurologic and psychiatric diseases.

Emerging therapies in traumatic brain injury

Despite decades of basic and clinical research, treatments to improve outcomes after traumatic brain injury (TBI) are limited. However, based on the recent recognition of the prevalence of mild TBI, and its potential link to neurodegenerative disease, many new and exciting secondary injury mechanisms have been identified and several new therapies are being evaluated targeting both classic and novel paradigms. This includes a robust increase in both preclinical and clinical investigations. Using a mechanism-based approach the authors define the targets and emerging therapies for TBI. They address putative new therapies for TBI across both the spectrum of injury severity and the continuum of care, from the field to rehabilitation. They discussTBI therapy using 11 categories, namely, (1) excitotoxicity and neuronal death, (2) brain edema, (3) mitochondria and oxidative stress, (4) axonal injury, (5) inflammation, (6) ischemia and cerebral blood flow dysregulation, (7) cognitive enhancement, (8) augmentation of endogenous neuroprotection, (9) cellular therapies, (10) combination therapy, and (11) TBI resuscitation. The current golden age of TBI research represents a special opportunity for the development of breakthroughs in the field.

Adenosine-associated delivery systems

Adenosine is a naturally occurring purine nucleoside in every cell. Many critical treatments such as modulating irregular heartbeat (arrhythmias), regulation of central nervous system (CNS) activity and inhibiting seizural episodes can be carried out using adenosine. Despite the significant potential therapeutic impact of adenosine and its derivatives, the severe side effects caused by their systemic administration have significantly limited their clinical use. In addition, due to adenosine's extremely short half-life in human blood (<10 s), there is an unmet need for sustained delivery systems to enhance efficacy and reduce side effects. In this article, various adenosine delivery techniques, including encapsulation into biodegradable polymers, cell-based delivery, implantable biomaterials and mechanical-based delivery systems, are critically reviewed and the existing challenges are highlighted.

ENT1 inhibition attenuates epileptic seizure severity via regulation of glutamatergic neurotransmission

Type 1 equilibrative nucleoside transporter (ENT1) promotes glutamate release by inhibition of adenosine signaling. However, whether ENT1 plays a role in epileptic seizure that involves elevated glutamatergic neurotransmission is unknown. Here, we report that both seizure rats and patients show increased expression of ENT1. Intrahippocampal injection of a specific inhibitor of ENT1, nitrobenzylthioinosine (NBTI), attenuates seizure severity and prolongs onset latency. In order to examine whether NBTI would be effective as antiepileptic after peripheral application, we injected NBTI intraperitoneally, and the results were similar to those obtained after intrahippocampal injection. NBTI administration leads to suppressed neuronal firing in seizure rats. In addition, increased mEPSC in seizure are inhibited by NBTI. Finally, NBTI results in deactivation of phosphorylated cAMP-response element-binding protein in the seizure rats. These results indicate that ENT1 plays an important role in the development of seizure. Inhibition of ENT1 might provide a novel therapeutic approach toward the control of epileptic seizure.

Adenosine kinase, glutamine synthetase and EAAT2 as gene therapy targets for temporal lobe epilepsy

Astrocytes are an attractive cell target for gene therapy, but the validation of new therapeutic candidates is needed. We determined whether adeno-associated viral (AAV) vector-mediated overexpression of glutamine synthetase (GS) or excitatory amino-acid transporter 2 (EAAT2), or expression of microRNA targeting adenosine kinase (miR-ADK) in hippocampal astrocytes in the rat brain could modulate susceptibility to kainate-induced seizures and neuronal cell loss. Transgene expression was found predominantly in astrocytes following direct injection of glial-targeting AAV9 vectors by 3 weeks postinjection. ADK expression in miR-ADK vector-injected rats was reduced by 94-96% and was associated with an ~50% reduction in the duration of kainate-induced seizures and greater protection of dentate hilar neurons but not CA3 neurons compared with miR-control vector-injected rats. In contrast, infusion of AAV-GS and EAAT2 vectors did not afford any protection against seizures or neuronal damage as the level of transcriptional activity of the glial fibrillary acidic promoter was too low to drive any significant increase in transgenic GS or EAAT2 relative to the high endogenous levels of these proteins. Our findings support ADK as a prime therapeutic target for gene therapy of temporal lobe epilepsy and suggest that alternative approaches including the use of stronger glial promoters are needed to increase transgenic GS and EAAT2 expression to levels that may be required to affect seizure induction and propagation.

Role of adenosine in the antiepileptic effects of deep brain stimulation

Despite the effectiveness of anterior thalamic nucleus (AN) deep brain stimulation (DBS) for the treatment of epilepsy, mechanisms responsible for the antiepileptic effects of this therapy remain elusive. As adenosine modulates neuronal excitability and seizure activity in animal models, we hypothesized that this nucleoside could be one of the substrates involved in the effects of AN DBS. We applied 5 days of stimulation to rats rendered chronically epileptic by pilocarpine injections and recorded epileptiform activity in hippocampal slices. We found that slices from animals given DBS had reduced hippocampal excitability and were less susceptible to develop ictal activity. In live animals, AN DBS significantly increased adenosine levels in the hippocampus as measured by microdialysis. The reduced excitability of DBS in vitro was completely abolished in animals pre-treated with A1 receptor antagonists and was strongly potentiated by A1 receptor agonists. We conclude that some of the antiepileptic effects of DBS may be mediated by adenosine.

Islet and stem cell encapsulation for clinical transplantation

Over the last decade, improvements in islet isolation techniques have made islet transplantation an option for a certain subset of patients with long-standing diabetes. Although islet transplants have shown improved graft function, adequate function beyond the second year has not yet been demonstrated, and patients still require immunosuppression to prevent rejection. Since allogeneic islet transplants have experienced some success, the next step is to improve graft function while eliminating the need for systemic immunosuppressive therapy. Biomaterial encapsulation offers a strategy to avoid the need for toxic immunosuppression while increasing the chances of graft function and survival. Encapsulation entails coating cells or tissue in a semipermeable biocompatible material that allows for the passage of nutrients, oxygen, and hormones while blocking immune cells and regulatory substances from recognizing and destroying the cell, thus avoiding the need for systemic immunosuppressive therapy. Despite advances in encapsulation technology, these developments have not yet been meaningfully translated into clinical islet transplantation, for which several factors are to blame, including graft hypoxia, host inflammatory response, fibrosis, improper choice of biomaterial type, lack of standard guidelines, and post-transplantation device failure. Several new approaches, such as the use of porcine islets, stem cells, development of prevascularized implants, islet nanocoating, and multilayer encapsulation, continue to generate intense scientific interest in this rapidly expanding field. This review provides a comprehensive update on islet and stem cell encapsulation as a treatment modality in type 1 diabetes, including a historical outlook as well as current and future research avenues.

Increased cortical extracellular adenosine correlates with seizure termination

OBJECTIVE

Seizures are currently defined by their electrographic features. However, neuronal networks are intrinsically dependent on neurotransmitters of which little is known regarding their periictal dynamics. Evidence supports adenosine as having a prominent role in seizure termination, as its administration can terminate and reduce seizures in animal models. Furthermore, microdialysis studies in humans suggest that adenosine is elevated periictally, but the relationship to the seizure is obscured by its temporal measurement limitations. Because electrochemical techniques can provide vastly superior temporal resolution, we test the hypothesis that extracellular adenosine concentrations rise during seizure termination in an animal model and humans using electrochemistry.

METHODS

White farm swine (n = 45) were used in an acute cortical model of epilepsy, and 10 human epilepsy patients were studied during intraoperative electrocorticography (ECoG). Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS)-based fast scan cyclic voltammetry (FSCV) and fixed potential amperometry were obtained utilizing an adenosine-specific triangular waveform or biosensors, respectively.

RESULTS

Simultaneous ECoG and electrochemistry demonstrated an average adenosine increase of 260% compared to baseline, at 7.5 ± 16.9 s with amperometry (n = 75 events) and 2.6 ± 11.2 s with FSCV (n = 15 events) prior to electrographic seizure termination. In agreement with these animal data, adenosine elevation prior to seizure termination in a human patient utilizing FSCV was also seen.

SIGNIFICANCE

Simultaneous ECoG and electrochemical recording supports the hypothesis that adenosine rises prior to seizure termination, suggesting that adenosine itself may be responsible for seizure termination. Future work using intraoperative WINCS-based FSCV recording may help to elucidate the precise relationship between adenosine and seizure termination.

Epigenetic changes induced by adenosine augmentation therapy prevent epileptogenesis

Epigenetic modifications, including changes in DNA methylation, lead to altered gene expression and thus may underlie epileptogenesis via induction of permanent changes in neuronal excitability. Therapies that could inhibit or reverse these changes may be highly effective in halting disease progression. Here we identify an epigenetic function of the brain's endogenous anticonvulsant adenosine, showing that this compound induces hypomethylation of DNA via biochemical interference with the transmethylation pathway. We show that inhibition of DNA methylation inhibited epileptogenesis in multiple seizure models. Using a rat model of temporal lobe epilepsy, we identified an increase in hippocampal DNA methylation, which correlates with increased DNA methyltransferase activity, disruption of adenosine homeostasis, and spontaneous recurrent seizures. Finally, we used bioengineered silk implants to deliver a defined dose of adenosine over 10 days to the brains of epileptic rats. This transient therapeutic intervention reversed the DNA hypermethylation seen in the epileptic brain, inhibited sprouting of mossy fibers in the hippocampus, and prevented the progression of epilepsy for at least 3 months. These data demonstrate that pathological changes in DNA methylation homeostasis may underlie epileptogenesis and reversal of these epigenetic changes with adenosine augmentation therapy may halt disease progression.

Adenosine, glutamate and pH: interactions and implications

Adenosine's role in the nervous system is multifaceted. As the core molecule of adenosine triphosphate (ATP), adenosine exists in equilibrium with the adenine nucleotide pool and contributes to cellular energy charge, a quantification of relative amounts of available ATP, ADP, AMP and adenosine. Beyond participating in overall energy balance and thus in maintaining cellular homeostasis, adenosine critically influences dynamic signaling in the nervous system. In particular, adenosine has an effect on and is affected by excitatory synaptic transmission. This report describes the ubiquitous nature of adenosine's influence, outlines specific scenarios of clinical import and highlights emerging knowledge about the regulation of adenosine.

ABT-702, an adenosine kinase inhibitor, attenuates inflammation in diabetic retinopathy

AIMS

This study was undertaken to determine the effect of an adenosine kinase inhibitor (AKI) in diabetic retinopathy (DR). We have shown previously that adenosine signaling via A2A receptors (A2AAR) is involved in retinal protection from diabetes-induced inflammation. Here we demonstrate that AKI-enhanced adenosine signaling provides protection from DR in mice.

MAIN METHODS

We targeted AK, the key enzyme in adenosine metabolism, using a treatment regime with the selective AKI, ABT-702 (1.5mg/kg intraperitoneally twice a week) commencing at the beginning of streptozotocin-induced diabetes at the age of eight weeks. This treatment, previously demonstrated to increase free adenosine levels in vivo, was maintained until the age of 16 weeks. Retinal inflammation was evaluated using Western blot, Real-Time PCR and immuno-staining analyses. Role of A2AAR signaling in the anti-inflammation effect of ABT-702 was analyzed in Amadori-glycated-albumin (AGA)-treated microglial cells.

KEY FINDINGS

At 16 weeks, when diabetic mice exhibit significant signs of retinal inflammation including up-regulation of oxidative/nitrosative stress, A2AAR, ENT1, Iba1, TNF-α, ICAM1, retinal cell death, and down-regulation of AK, the ABT-702 treated group showed lower signs of inflammation compared to control animals receiving the vehicle. The involvement of adenosine signaling in the anti-inflammation effect of ABT-702 was supported by the TNF-α release blocking effect of A2AAR antagonist in AGA-treated microglial cells.

SIGNIFICANCE

These results suggest a role for AK in regulating adenosine receptor signaling in the retina. Inhibition of AK potentially amplifies the therapeutic effects of site- and event-specific accumulation of extracellular adenosine, which is of highly translational impact.

Adenosine kinase: exploitation for therapeutic gain

Adenosine kinase (ADK; EC 2.7.1.20) is an evolutionarily conserved phosphotransferase that converts the purine ribonucleoside adenosine into 5'-adenosine-monophosphate. This enzymatic reaction plays a fundamental role in determining the tone of adenosine, which fulfills essential functions as a homeostatic and metabolic regulator in all living systems. Adenosine not only activates specific signaling pathways by activation of four types of adenosine receptors but it is also a primordial metabolite and regulator of biochemical enzyme reactions that couple to bioenergetic and epigenetic functions. By regulating adenosine, ADK can thus be identified as an upstream regulator of complex homeostatic and metabolic networks. Not surprisingly, ADK dysfunction is involved in several pathologies, including diabetes, epilepsy, and cancer. Consequently, ADK emerges as a rational therapeutic target, and adenosine-regulating drugs have been tested extensively. In recent attempts to improve specificity of treatment, localized therapies have been developed to augment adenosine signaling at sites of injury or pathology; those approaches include transplantation of stem cells with deletions of ADK or the use of gene therapy vectors to downregulate ADK expression. More recently, the first human mutations in ADK have been described, and novel findings suggest an unexpected role of ADK in a wider range of pathologies. ADK-regulating strategies thus represent innovative therapeutic opportunities to reconstruct network homeostasis in a multitude of conditions. This review will provide a comprehensive overview of the genetics, biochemistry, and pharmacology of ADK and will then focus on pathologies and therapeutic interventions. Challenges to translate ADK-based therapies into clinical use will be discussed critically.

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.

The role of astroglia in the epileptic brain

Epilepsies comprise a family of multifactorial neurological disorders that affect at least 50 million people worldwide. Despite a long history of neurobiological and clinical studies the mechanisms that lead the brain network to a hyperexcitable state and to the intense, massive neuronal discharges reflecting a seizure episode are only partially defined. Most epilepsies of genetic origin are related to mutations in ionic channels that cause neuronal hyperexcitability. However, idiopathic epilepsies of unclear origin represent the majority of these brain disorders. A large body of evidence suggests that in the epileptic brain neurons are not the only players. Indeed, the glial cell astrocyte is known to be morphologically and functionally altered in different types of epilepsy. Although it is unclear whether these astrocyte dysfunctions can have a causative role in epileptogenesis, the hypothesis that astrocytes contribute to epileptiform activities recently received a considerable experimental support. Notably, currently used antiepileptic drugs, that act mainly on neuronal ion channels, are ineffective in a large group of patients. Clarifying astrocyte functions in the epileptic brain tissue could unveil astrocytes as novel therapeutic targets. In this review we present first a short overview on the role of astrocytes in the epileptic brain starting from the "historical" observations on their fundamental modulation of brain homeostasis, such as the control of water content, ionic equilibrium, and neurotransmitters concentrations. We then focus our review on most recent studies that hint at a distinct contribution of these cells in the generation of focal epileptiform activities.