Adenosine-based cell therapy approaches for pharmacoresistant epilepsies

Reactive A1 Astrocyte-Targeted Nucleic Acid Nanoantiepileptic Drug Downregulating Adenosine Kinase to Rescue Endogenous Antiepileptic Pathway

Resistance to traditional antiepileptic drugs is a major challenge in chronic epilepsy treatment. MicroRNA-based gene therapy is a promising alternative but has demonstrated limited efficacy due to poor blood-brain barrier permeability, cellular uptake, and targeting efficiency. Adenosine is an endogenous antiseizure agent deficient in the epileptic brain due to elevated adenosine kinase (ADK) activity in reactive A1 astrocytes. We designed a nucleic acid nanoantiepileptic drug (tFNA-ADK^ASO@AS1) based on a tetrahedral framework nucleic acid (tFNA), carrying an antisense oligonucleotide targeting ADK (ADK^ASO) and A1 astrocyte-targeted peptide (AS1). This tFNA-ADK^ASO@AS1 construct effectively reduced brain ADK, increased brain adenosine, mitigated aberrant mossy fiber sprouting, and reduced the recurrent spontaneous epileptic spike frequency in a mouse model of chronic temporal lobe epilepsy. Further, the treatment did not induce any neurotoxicity or major organ damage. This work provides proof-of-concept for a novel antiepileptic drug delivery strategy and for endogenous adenosine as a promising target for gene-based modulation.

A peptide blocking the ADORA1-neurabin interaction is anticonvulsant and inhibits epilepsy in an Alzheimer's model

Epileptic seizures are common sequelae of stroke, acute brain injury, and chronic neurodegenerative diseases, including Alzheimer's disease (AD), and cannot be effectively controlled in approximately 40% of patients, necessitating the development of novel therapeutic agents. Activation of the A1 receptor (A1R) by endogenous adenosine is an intrinsic mechanism to self-terminate seizures and protect neurons from excitotoxicity. However, targeting A1R for neurological disorders has been hindered by side effects associated with its broad expression outside the nervous system. Here we aim to target the neural-specific A1R/neurabin/regulator of G protein signaling 4 (A1R/neurabin/RGS4) complex that dictates A1R signaling strength and response outcome in the brain. We developed a peptide that blocks the A1R-neurabin interaction to enhance A1R activity. Intracerebroventricular or i.n. administration of this peptide shows marked protection against kainate-induced seizures and neuronal death. Furthermore, in an AD mouse model with spontaneous seizures, nasal delivery of this blocking peptide reduces epileptic spike frequency. Significantly, the anticonvulsant and neuroprotective effects of this peptide are achieved through enhanced A1R function in response to endogenous adenosine in the brain, thus, avoiding side effects associated with A1R activation in peripheral tissues and organs. Our study informs potentially new anti-seizure therapy applicable to epilepsy and other neurological illness with comorbid seizures.

Equilibrative Nucleoside Transporters-1 Inhibitors Act as Anti-epileptic Agents by Inhibiting Glutamatergic Transmission

Background and Purpose: Adenosine dysregulation is associated with the occurrence of the epilepsy and equilibrative nucleoside transporters-1 (ENT-1) functions as an important regulator of extracellular adenosine in the brain. This study was aimed to prove the anti-epileptic effect of BBB permeable ENT-1 inhibitors, JMF1907 and J4, on animal models of various epilepsy, and the mechanisms that are involved. Experimental Approach: Maximal electroshock seizure (MES), pentylenetetrazol (PTZ)-induced seizure and kindling models were used as mouse models of generalized tonic-clonic epilepsy, generalized myoclonic epilepsy, and partial epilepsy, respectively. The epilepsy frequency, duration, and Racine score were evaluated. Whole-cell recordings were made from the hippocampal dentate granule cells by using a patch-clamp technique in the brain slice of the mice. Key Results: In MES, JMF1907 at a dose of 5 mg kg^-1 was efficacious in decreasing hindlimb extension, while J4 did not decrease hindlimb extension until a higher dose (10 mg kg^-1). Both JMF1907 and J4 were more potent in lengthening onset latency than ethosuximide (ETH) in PTZ-induced myoclonic epilepsy model, whereas ETH had better effects on the Racine score. In kindling model, JMF1907 and J4 at a dose of 1 mg kg^-1 had effects on seizure frequency and duration, and the effects of JMF1907 were comparable with those of carbamazepine. Both JMF1907 and J4 can reduce the glutamatergic spontaneous excitatory post-synaptic currents (sEPSCs) frequency. The maximal inhibition was about 50% for JMF1907 at a concentration of 1 μg L^-1, whereas J4 only inhibited 40% of sEPSCs frequency at a dose of 10 μg L^-1. Conclusion and Implications: ENT-1 inhibitors, JMF1907 and J4, showed anti-epileptic effects in different epilepsy models and the effects involved pre-synaptic neuronal modulation.

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.

Adenosine Augmentation Evoked by an ENT1 Inhibitor Improves Memory Impairment and Neuronal Plasticity in the APP/PS1 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive impairment and synaptic dysfunction. Adenosine is an important homeostatic modulator that controls the bioenergetic network in the brain through regulating receptor-evoked signaling pathways, bioenergetic machineries, and epigenetic-mediated gene regulation. Equilibrative nucleoside transporter 1 (ENT1) is a major adenosine transporter that recycles adenosine from the extracellular space. In the present study, we report that a small adenosine analogue (designated J4) that inhibited ENT1 prevented the decline in spatial memory in an AD mouse model (APP/PS1). Electrophysiological and biochemical analyses further demonstrated that chronic treatment with J4 normalized the impaired basal synaptic transmission and long-term potentiation (LTP) at Schaffer collateral synapses as well as the aberrant expression of synaptic proteins (e.g., NR2A and NR2B), abnormal neuronal plasticity-related signaling pathways (e.g., PKA and GSK3β), and detrimental elevation in astrocytic A_2AR expression in the hippocampus and cortex of APP/PS1 mice. In conclusion, our findings suggest that modulation of adenosine homeostasis by J4 is beneficial in a mouse model of AD. Our study provides a potential therapeutic strategy to delay the progression of AD.

Epilepsy and astrocyte energy metabolism

Epilepsy is a complex neurological syndrome characterized by neuronal hyperexcitability and sudden, synchronized electrical discharges that can manifest as seizures. It is now increasingly recognized that impaired astrocyte function and energy homeostasis play key roles in the pathogenesis of epilepsy. Excessive neuronal discharges can only happen, if adequate energy sources are made available to neurons. Conversely, energy depletion during seizures is an endogenous mechanism of seizure termination. Astrocytes control neuronal energy homeostasis through neurometabolic coupling. In this review, we will discuss how astrocyte dysfunction in epilepsy leads to distortion of key metabolic and biochemical mechanisms. Dysfunctional glutamate metabolism in astrocytes can directly contribute to neuronal hyperexcitability. Closure of astrocyte intercellular gap junction coupling as observed early during epileptogenesis limits activity-dependent trafficking of energy metabolites, but also impairs clearance of the extracellular space from accumulation of K⁺ and glutamate. Dysfunctional astrocytes also increase the metabolism of adenosine, a metabolic product of ATP degradation that broadly inhibits energy-consuming processes as an evolutionary adaptation to conserve energy. Due to the critical role of astroglial energy homeostasis in the control of neuronal excitability, metabolic therapeutic approaches that prevent the utilization of glucose might represent a potent antiepileptic strategy. In particular, high fat low carbohydrate "ketogenic diets" as well as inhibitors of glycolysis and lactate metabolism are of growing interest for the therapy of epilepsy.

Pediatric Sudden Unexpected Death in Epilepsy: What Have we Learned from Animal and Human Studies, and Can we Prevent it?

Several factors, such as epilepsy syndrome, poor compliance, and increased seizure frequency increase the risks of sudden unexpected death in epilepsy (SUDEP). Animal models have revealed that the mechanisms of SUDEP involve initially a primary event, often a seizure of sufficient type and severity, that occurs in a brain, which is vulnerable to SUDEP due to either genetic or antecedent factors. This primary event initiates a cascade of secondary events starting, as some models indicate, with cortical spreading depolarization that propagates to the brainstem where it results in autonomic dysfunction. Intrinsic abnormalities in brainstem serotonin, adenosine, sodium-postassium ATPase, and respiratory-control systems are also important. The tertiary event, which results from the above dysfunction, consists of either lethal central apnea, pulmonary edema, or arrhythmia. Currently, it is necessary to (1) continue researching SUDEP mechanisms, (2) work on reducing SUDEP risk factors, and (3) address the major need to counsel families about SUDEP.

Reduction of epileptiform activity through local valproate-implants in a rat neocortical epilepsy model

PURPOSE

Pharmacotherapy of epilepsies is limited due to low concentrations at epileptogenic foci, side effects of high systemic doses and that some potentially efficient substances do not pass the blood-brain barrier. To overcome these limitations, we tested the efficacy of local valproate (VPA)-containing polymer implants in a model of necocortical injected tetanus toxin (TeT) in the rat.

METHODS

Tetanus toxin was injected intracortically and cobalt (II) chloride (CoCl2) was applied on the cortical surface. Video-electrocorticography recordings with intracortical electrodes were performed. VPA-containing polymers were implanted above the cortical focus. Antiepileptic effects were evaluated as reductions of epileptiform potentials (EPs) per hour in comparison to saline (NaCl)-containing polymer implants.

RESULTS

Triple 50ng TeT injections plus CoCl2 application (20/10mg) showed consistent EPs. NaCl-implanted animals (n=6) showed a mean of 10.5EPs/h after the first week, the EP frequency increased to 53.5EPs/h after the second week. VPA-implant animals (n=5) showed a reduction in EP frequency from 71.6 to 4.8EPs/h after the second week. The EP frequency after the second week was higher in the NaCl-implanted animals than in the VPA-implanted (p=0.0303). The mean EPs/h increase in NaCl-implanted rats (+42.9EPs/h) was different (p=0.0087) from the mean EPs/h decrease in VPA-implanted rats (-66.8EPs/h).

CONCLUSION

Despite former publications no clear seizures could be reproduced but it was possible to establish focal EPs, which proved to be a reliable marker for epileptic activity. Local antiepileptic therapy with VPA has shown efficacy in decreasing EP frequency.

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.

The Role of Piriform Cortex Adenosine A1 Receptors on Hippocampal Kindling

Introduction:

The hippocampus and piriform cortex have a critical role in seizure propagation. In this study, the role of adenosine A1 receptors of piriform cortex on CA1 hippocampal kindled seizures was studied in rats.

Methods:

Animals were implanted with a tripolar electrode in the right hippocampal CA1 region and two guide cannulae in the left and right piriform cortex. They were kindled by daily electrical stimulation of hippocampus. In fully kindled rats, N6- cyclohexyladenosine (CHA; a selective adenosine A1 receptors agonist) and 1, 3-dimethyl-8-cyclopenthylxanthine (CPT a selective adenosine A1 receptor antagonist) were microinfused into the piriform cortex. The animals were stimulated at 5, 15 and 90 minutes (min) after drag injection.

Results:

Obtained data showed that CHA (10 and 100 μM) reduced afterdischarge duration, stage 5 seizure duration, and total seizure duration at 5 and 15 min after drag injection. There was no significant change in latency to stage 4 seizure. CPT at concentration of 20 μM increased afterdischarge duration, stage 5 seizure duration, and total seizure duration and decreased latency to stage 4 seizure at 5 and 15 min post injection. Pretreatment of rats with CPT (10 μM), 5 min before CHA (100 μM), reduced the effect of CHA on seizure parameters.

Conclusion:

These results suggested that activity of adenosine A1 receptors in the piriform cortex has an anticonvulsant effect on kindled seizures resulting from electrical stimulation of the CA1 region of the hippocampus.

A Molecular Approach to Epilepsy Management: from Current Therapeutic Methods to Preconditioning Efforts

Epilepsy is the most common and chronic neurological disorder characterized by recurrent unprovoked seizures. The key aim in treating patients with epilepsy is the suppression of seizures. An understanding of focal changes that are involved in epileptogenesis may therefore provide novel approaches for optimal treatment of the seizure. Although the actual pathogenesis of epilepsy is still uncertain, recently growing lines of evidence declare that microglia and astrocyte activation, oxidative stress and reactive oxygen species (ROS) production, mitochondria dysfunction, and damage of blood-brain barrier (BBB) are involved in its pathogenesis. Impaired GABAergic function in the brain is probably the most accepted hypothesis regarding the pathogenesis of epilepsy. Clinical neuroimaging of patients and experimental modeling have demonstrated that seizures may induce neuronal apoptosis. Apoptosis signaling pathways are involved in the pathogenesis of several types of epilepsy such as temporal lobe epilepsy (TLE). The quality of life of patients is seriously affected by treatment-related problems and also by unpredictability of epileptic seizures. Moreover, the available antiepileptic drugs (AED) are not significantly effective to prevent epileptogenesis. Thus, novel therapies that are proficient to control seizure in people who are suffering from epilepsy are needed. The preconditioning method promises to serve as an alternative therapeutic approach because this strategy has demonstrated the capability to curtail epileptogenesis. For this reason, understanding of molecular mechanisms underlying brain tolerance induced by preconditioning is crucial to delineate new neuroprotective ways against seizure damage and epileptogenesis. In this review, we summarize the work to date on the pathogenesis of epilepsy and discuss recent therapeutic strategies in the treatment of epilepsy. We will highlight that novel therapy targeting such as preconditioning process holds great promise. In addition, we will also highlight the role of gene reprogramming and mitochondrial biogenesis in the preconditioning-mediated neuroprotective events.

Adenosine: setting the stage for plasticity

It is widely accepted that Hebbian forms of plasticity mediate selective modifications in synaptic strength underlying information encoding in response to experience and circuit formation or refinement throughout development. Several complementary forms of homeostatic plasticity coordinate to keep Hebbian plasticity in check, frequently through the actions of conserved regulatory molecules. Recent evidence suggests that this may be the case for adenosine, which is ubiquitous in the brain and is released by both neurons and glial cells via constitutive and activity-dependent mechanisms. Through A1 and A2A receptor activation, adenosine modulates neuronal homeostasis and tunes the ability of synapses to undergo and/or sustain plasticity. Here, we review how adenosine equilibrates neuronal activity and sets the stage for synaptic plasticity.

Adenosine augmentation ameliorates psychotic and cognitive endophenotypes of schizophrenia

An emerging theory of schizophrenia postulates that hypofunction of adenosine signaling may contribute to its pathophysiology. This study was designed to test the "adenosine hypothesis" of schizophrenia and to evaluate focal adenosine-based strategies for therapy. We found that augmentation of adenosine by pharmacologic inhibition of adenosine kinase (ADK), the key enzyme of adenosine clearance, exerted antipsychotic-like activity in mice. Further, overexpression of ADK in transgenic mice was associated with attentional impairments linked to schizophrenia. We observed that the striatal adenosine A2A receptor links adenosine tone and psychomotor response to amphetamine, an indicator of dopaminergic signaling. Finally, intrastriatal implants of engineered adenosine-releasing cells restored the locomotor response to amphetamine in mice overexpressing ADK, whereas the same grafts placed proximal to the hippocampus of transgenic mice reversed their working memory deficit. This functional double dissociation between striatal and hippocampal adenosine demonstrated in Adk transgenic mice highlights the independent contributions of these two interconnected brain regions in the pathophysiology of schizophrenia and thus provides the rationale for developing local adenosine augmentation therapies for the treatment of schizophrenia.

Neurabin scaffolding of adenosine receptor and RGS4 regulates anti-seizure effect of endogenous adenosine

Endogenous adenosine is an essential protective agent against neural damage by various insults to the brain. However, the therapeutic potential of adenosine receptor-directed ligands for neuroprotection is offset by side effects in peripheral tissues and organs. An increase in adenosine receptor responsiveness to endogenous adenosine would enhance neuroprotection while avoiding the confounding effects of exogenous ligands. Here we report novel regulation of adenosine-evoked responses by a neural tissue-specific protein, neurabin. Neurabin attenuated adenosine A(1) receptor (A1R) signaling by assembling a complex between the A1R and the regulator of G-protein signaling 4 (RGS4), a protein known to turn off G-protein signaling. Inactivation of the neurabin gene enhanced A1R signaling and promoted the protective effect of adenosine against excitotoxic seizure and neuronal death in mice. Furthermore, administration of a small molecule inhibitor of RGS4 significantly attenuated seizure severity in mice. Notably, the dose of kainate capable of inducing an ∼50% rate of death in wild-type (WT) mice did not affect neurabin-null mice or WT mice cotreated with an RGS4 inhibitor. The enhanced anti-seizure and neuroprotective effect achieved by disruption of the A1R/neurabin/RGS4 complex is elicited by the on-site and on-demand release of endogenous adenosine, and does not require administration of A1R ligands. These data identify neurabin-RGS4 as a novel tissue-selective regulatory mechanism for fine-tuning adenosine receptor function in the nervous system. Moreover, these findings implicate the A1R/neurabin/RGS4 complex as a valid therapeutic target for specifically manipulating the neuroprotective effects of endogenous adenosine.

Adenosine, ketogenic diet and epilepsy: the emerging therapeutic relationship between metabolism and brain activity

For many years the neuromodulator adenosine has been recognized as an endogenous anticonvulsant molecule and termed a “retaliatory metabolite.” As the core molecule of ATP, adenosine forms a unique link between cell energy and neuronal excitability. In parallel, a ketogenic (high-fat, low-carbohydrate) diet is a metabolic therapy that influences neuronal activity significantly, and ketogenic diets have been used successfully to treat medically-refractory epilepsy, particularly in children, for decades. To date the key neural mechanisms underlying the success of dietary therapy are unclear, hindering development of analogous pharmacological solutions. Similarly, adenosine receptor–based therapies for epilepsy and myriad other disorders remain elusive. In this review we explore the physiological regulation of adenosine as an anticonvulsant strategy and suggest a critical role for adenosine in the success of ketogenic diet therapy for epilepsy. While the current focus is on the regulation of adenosine, ketogenic metabolism and epilepsy, the therapeutic implications extend to acute and chronic neurological disorders as diverse as brain injury, inflammatory and neuropathic pain, autism and hyperdopaminergic disorders. Emerging evidence for broad clinical relevance of the metabolic regulation of adenosine will be discussed.

Quantitative analysis of adenosine using liquid chromatography/atmospheric pressure chemical ionization-tandem mass spectrometry (LC/APCI-MS/MS)

Adenosine-secreting cellular brain implants constitute a promising therapeutic approach for the treatment of epilepsy. To engineer neural stem cells for therapeutic adenosine delivery, a reliable and fast analytical method is necessary to quantify cell-based adenosine release. Here we describe the development, optimization and validation of adenosine measurement using liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (LC-APCI-MS/MS). LC-MS/MS in positive ion mode used selected reaction monitoring at m/z of 268.2/136.1 and 302.2/170.0 for adenosine and the internal standard, respectively. The bias was within 15% of the nominal value and evaluation of precision showed a relative standard deviation lower than 15% for all measured concentrations. The lower limit of quantification of adenosine was 15.6 ng/ml. Freeze and thaw stability and processed sample stability also fulfilled the acceptance criteria. Evaluation of the matrix effect showed that the method is not affected by relative matrix effects. The major advantages of this method are the absence of an extraction phase and the combination of the high selectivity and sensitivity characteristic for the LC-MS/MS technique, with a short run time of 4.5 min. These results demonstrate that this method is a useful tool to measure adenosine concentrations in culture medium released from stem cells in vitro.

Comonitoring of adenosine and dopamine using the Wireless Instantaneous Neurotransmitter Concentration System: proof of principle

OBJECT

The authors of previous studies have demonstrated that local adenosine efflux may contribute to the therapeutic mechanism of action of thalamic deep brain stimulation (DBS) for essential tremor. Real-time monitoring of the neurochemical output of DBS-targeted regions may thus advance functional neurosurgical procedures by identifying candidate neurotransmitters and neuromodulators involved in the physiological effects of DBS. This would in turn permit the development of a method of chemically guided placement of DBS electrodes in vivo. Designed in compliance with FDA-recognized standards for medical electrical device safety, the authors report on the utility of the Wireless Instantaneous Neurotransmitter Concentration System (WINCS) for real-time comonitoring of electrical stimulation-evoked adenosine and dopamine efflux in vivo, utilizing fast-scan cyclic voltammetry (FSCV) at a polyacrylonitrile-based (T-650) carbon fiber microelectrode (CFM).

METHODS

The WINCS was used for FSCV, which consisted of a triangle wave scanned between -0.4 and +1.5 V at a rate of 400 V/second and applied at 10 Hz. All voltages applied to the CFM were with respect to an Ag/AgCl reference electrode. The CFM was constructed by aspirating a single T-650 carbon fiber (r = 2.5 microm) into a glass capillary and pulling to a microscopic tip using a pipette puller. The exposed carbon fiber (the sensing region) extended beyond the glass insulation by approximately 50 microm. Proof of principle tests included in vitro measurements of adenosine and dopamine, as well as in vivo measurements in urethane-anesthetized rats by monitoring adenosine and dopamine efflux in the dorsomedial caudate putamen evoked by high-frequency electrical stimulation of the ventral tegmental area and substantia nigra.

RESULTS

The WINCS provided reliable, high-fidelity measurements of adenosine efflux. Peak oxidative currents appeared at +1.5 V and at +1.0 V for adenosine, separate from the peak oxidative current at +0.6 V for dopamine. The WINCS detected subsecond adenosine and dopamine efflux in the caudate putamen at an implanted CFM during high-frequency stimulation of the ventral tegmental area and substantia nigra. Both in vitro and in vivo testing demonstrated that WINCS can detect adenosine in the presence of other easily oxidizable neurochemicals such as dopamine comparable to the detection abilities of a conventional hardwired electrochemical system for FSCV.

CONCLUSIONS

Altogether, these results demonstrate that WINCS is well suited for wireless monitoring of high-frequency stimulation-evoked changes in brain extracellular concentrations of adenosine. Clinical applications of selective adenosine measurements may prove important to the future development of DBS technology.

Silk fibroin encapsulated powder reservoirs for sustained release of adenosine

Due to its unique properties, silk fibroin was studied as a biodegradable polymer vehicle for sustained, local delivery of the anticonvulsant adenosine from encapsulated reservoirs. Silk is a biologically derived protein polymer that is biocompatible, mechanically strong and degrades to non-toxic products in vivo. To achieve local, sustained, controlled adenosine release from fully degradable implants, solid adenosine powder reservoirs were coated with silk fibroin. Material properties of the silk coating including thickness, crystallinity and morphology were investigated to assess the relationships between silk coating biomaterial features and adenosine release from silk encapsulated reservoirs. Reservoir coating thickness was varied through manipulation of the silk coating solution concentration and number of coatings applied. Release studies were also performed in proteinase type XIV to model the effects of degradation. Increasing the barrier to diffusion, either by increasing coating thickness or crystallinity was found to delay adenosine burst, decrease average daily release rate, and increase duration of release. In the case of encapsulated reservoirs coated with eight layers of 8% (w/v) silk, a linear release profile was observed and adenosine release was sustained for 14days. The ability to achieve nearly constant release for 2weeks for adenosine via control of the silk coating suggests these encapsulated reservoirs represent a novel system for delivering adenosine. We anticipate that this approach could also be extended to other implant needs and small-molecule drugs to treat a range of clinical needs.

Adenosine dysfunction in astrogliosis: cause for seizure generation?

Epilepsy is characterized by both neuronal and astroglial dysfunction. The endogenous anticonvulsant adenosine, the level of which is largely controlled by astrocytes, might provide a crucial link between astrocyte and neuron dysfunction in epilepsy. Here we have studied astrogliosis, a hallmark of the epileptic brain, adenosine dysfunction and the emergence of spontaneous seizures in a comprehensive approach that includes a new mouse model of focal epileptogenesis, mutant mice with altered brain levels of adenosine, and mice lacking adenosine A1 receptors. In wild-type mice, following a focal epileptogenesis-precipitating injury, astrogliosis, upregulation of the adenosine-removing astrocytic enzyme adenosine kinase (ADK), and spontaneous seizures coincide in a spatio-temporally restricted manner. Importantly, these spontaneous seizures are mimicked by untreated transgenic mice that either overexpress ADK in brain or lack A1 receptors. Conversely, mice with reduced ADK in the forebrain do not develop either astrogliosis or spontaneous seizures. Our studies define ADK as a crucial upstream regulator of A1 receptor-mediated modulation of neuronal excitability, and support the ADK hypothesis of epileptogenesis in which upregulation of ADK during astrogliosis provides a crucial link between astrocyte and neuron dysfunction in epilepsy. These findings define ADK as rational target for therapeutic intervention.

Uncoupling of astrogliosis from epileptogenesis in adenosine kinase (ADK) transgenic mice

The astrocytic enzyme adenosine kinase (ADK) is a key negative regulator of the brain's endogenous anticonvulsant adenosine. Astrogliosis with concomitant upregulation of ADK is part of the epileptogenic cascade and contributes to seizure generation. To molecularly dissect the respective roles of astrogliosis and ADK-expression for seizure generation, we used a transgenic approach to uncouple ADK-expression from astrogliosis: in Adk-tg mice the endogenous Adk-gene was deleted and replaced by a ubiquitously expressed Adk-transgene with novel ectopic expression in pyramidal neurons, resulting in spontaneous seizures. Here, we followed a unique approach to selectively injure the CA3 of these Adk-tg mice. Using this strategy, we had the opportunity to study astrogliosis and epileptogenesis in the absence of the endogenous astrocytic Adk-gene. After triggering epileptogenesis we demonstrate astrogliosis without upregulation of ADK, but lack of seizures, whereas matching wild-type animals developed astrogliosis with upregulation of ADK and spontaneous recurrent seizures. By uncoupling ADK-expression from astrogliosis, we demonstrate that global expression levels of ADK rather than astrogliosis per se contribute to seizure generation.

A novel mouse model for sudden unexpected death in epilepsy (SUDEP): role of impaired adenosine clearance

Sudden unexpected death in epilepsy (SUDEP) is a significant cause of mortality in people with epilepsy. Two postulated causes for SUDEP, cardiac and respiratory depression, can both be explained by overstimulation of adenosine receptors. We hypothesized that SUDEP is a consequence of a surge in adenosine as a result of prolonged seizures combined with deficient adenosine clearance; consequently, blockade of adenosine receptors should prevent SUDEP. Here we induced impaired adenosine clearance in adult mice by pharmacologic inhibition of the adenosine-removing enzymes, adenosine kinase and deaminase. Combination of impaired adenosine clearance with kainic acid-induced seizures triggered sudden death in all animals. Most importantly, the adenosine receptor antagonist caffeine, when given after seizure onset, increased survival from 23.75 +/- 1.35 min to 54.86 +/- 6.59 min (p < 0.01). Our data indicate that SUDEP is due to overactivation of adenosine receptors and that caffeine treatment after seizure onset might be beneficial.

Antiepileptic effects of silk-polymer based adenosine release in kindled rats

Pharmacotherapy for epilepsy is limited by high incidence of pharmacoresistance and failure to prevent development and progression of epilepsy. Using the rat hippocampal kindling model, we report on the therapeutic potential of novel silk-based polymers engineered to release the anticonvulsant adenosine. Polymers were designed to release 1000 ng adenosine per day during a time span of ten days. In the first experiment rats were kindled by hippocampal electrical stimulation until all animals reacted with stage 5 seizures. Adenosine-releasing or control polymers were then implanted into the infrahippocampal fissure ipsilateral to the site of stimulation. Subsequently, only recipients of adenosine-releasing implants were completely protected from generalized seizures over a period of ten days corresponding to the duration of sustained adenosine release. To monitor seizure development in the presence of adenosine, adenosine-releasing or control polymers were implanted prior to kindling. After 30 stimulations--delivered from days 4 to 8 after implantation--control animals had developed convulsive stage 5 seizures, whereas recipients of adenosine-releasing implants were still protected from convulsive seizures. Kindling was resumed after nine days to allow expiration of adenosine release. During additional 30 stimulations, recipients of adenosine-releasing implants gradually resumed kindling development at seizure stages corresponding to those when kindling was initially suspended, while control rats resumed kindling development at convulsive seizure stages. Blockade of adenosine A1 receptors did not exacerbate seizures in protected animals. We conclude that silk-based adenosine delivery exerts potent anti-ictogenic effects, but might also have at least partial anti-epileptogenic effects. Thus, silk-based adenosine augmentation holds promise for the treatment of epilepsy.

Engineered adenosine-releasing cells for epilepsy therapy: human mesenchymal stem cells and human embryonic stem cells

Adenosine is a modulator of neuronal activity with anticonvulsant and neuroprotective properties. Conversely, focal deficiency in adenosine contributes to ictogenesis. Thus, focal reconstitution of adenosine within an epileptogenic brain region constitutes a rational therapeutic approach, whereas systemic augmentation of adenosine is precluded by side effects. To meet the therapeutic goal of focal adenosine augmentation, genetic disruption of the adenosine metabolizing enzyme, adenosine kinase (ADK) in rodent cells was used as a molecular strategy to induce adenosine release from cellular brain implants, which demonstrated antiepileptic and neuroprotective properties. Currently, the second generation of adenosine-releasing cells is under development based on the rationale to use human stem cell-derived brain implants to avoid xenotransplantation. To effectively engineer human stem cells to release adenosine, a lentiviral vector was constructed to express inhibitory micro-RNA directed against ADK. Lentiviral knockdown of ADK induced therapeutic adenosine release in human mesenchymal stem cells, which reduced acute injury and seizures, as well as chronic seizures, when grafted into the mouse hippocampus. The therapeutic potential of this approach suggests the feasibility to engineer autologous adenosine-releasing stem cells derived from a patient. Human embryonic stem cells (hESCs) have a high proliferative capacity and can be subjected to specific cellular differentiation pathways. hESCs, differentiated in vitro into neuroepithelial cells and grafted into the mouse brain, displayed intrahippocampal location and neuronal morphology. Using the same lentiviral micro-RNA vector, we demonstrated knockdown of ADK in hESCs. New developments and therapeutic challenges in using human mesenchymal stem cells and hESCs for epilepsy therapy will be critically evaluated.

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

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

Human mesenchymal stem cell grafts engineered to release adenosine reduce chronic seizures in a mouse model of CA3-selective epileptogenesis

A novel generation of silk-based brain implants engineered to release adenosine was recently shown to provide robust seizure suppression in kindled rats. As a first step to develop stem cell-coated silk-based 3D-scaffolds for the therapeutic long-term delivery of adenosine we engineered human mesenchymal stem cells (hMSCs) to release adenosine. Here we demonstrate reduction of chronic seizures in a mouse model of CA3-selective epileptogenesis after infrahippocampal transplantation of adenosine-releasing hMSCs.

Ang II and Ang IV: unraveling the mechanism of action on synaptic plasticity, memory, and epilepsy

The central angiotensin system plays a crucial role in cardiovascular regulation. More recently, angiotensin peptides have been implicated in stress, anxiety, depression, cognition, and epilepsy. Angiotensin II (Ang II) exerts its actions through AT(1) and AT(2) receptors, while most actions of its metabolite Ang IV were believed to be independent of AT(1) or AT(2) receptor activation. A specific binding site with high affinity for Ang IV was discovered and denominated "AT(4) receptor". The beneficiary effects of AT(4) ligands in animal models for cognitive impairment and epileptic seizures initiated the search for their mechanism of action. This proved to be a challenging task, and after 20 years of research, the nature of the "AT(4) receptor" remains controversial. Insulin-regulated aminopeptidase (IRAP) was first identified as the high-affinity binding site for AT(4) ligands. Recently, the hepatocyte growth factor receptor c-MET was also proposed as a receptor for AT(4) ligands. The present review focuses on the effects of Ang II and Ang IV on synaptic transmission and plasticity, learning, memory, and epileptic seizure activity. Possible interactions of Ang IV with the classical AT(1) and AT(2) receptor subtypes are evaluated, and other potential mechanisms by which AT(4) ligands may exert their effects are discussed. Identification of these mechanisms may provide a valuable target in the development in novel drugs for the treatment of cognitive disorders and epilepsy.

Astrocytic adenosine kinase regulates basal synaptic adenosine levels and seizure activity but not activity-dependent adenosine release in the hippocampus

Adenosine is an endogenous inhibitor of excitatory synaptic transmission with potent anticonvulsant properties in the mammalian brain. Given adenosine's important role in modulating synaptic transmission, several mechanisms exist to regulate its extracellular availability. One of these is the intracellular enzyme adenosine kinase (ADK), which phosphorylates adenosine to AMP. We have investigated the role that ADK plays in regulating the presence and effects of extracellular adenosine in area CA1 of rat hippocampal slices. Inhibition of ADK activity with 5'-iodotubercidin (IODO; 5 muM) raised extracellular adenosine, as measured with adenosine biosensors, and potently inhibited field excitatory post-synaptic potentials (fEPSPs) in an adenosine A(1)R-dependent manner. In nominally Mg(2+)-free aCSF, which facilitated the induction of electrically-evoked epileptiform activity, adenosine biosensor recordings revealed that seizures were accompanied by the transient release of adenosine. Under these conditions, IODO also inhibited the fEPSP and greatly suppressed epileptiform activity evoked by brief, high-frequency stimulation. During spontaneous seizures evoked by the A(1)R antagonist CPT, adenosine release was unaffected by IODO. This suggests that ADK activity does not limit activity-dependent adenosine release. On the basis of strong ADK immunoreactivity in GFAP-positive cells, astrocytes are likely to play a key role in regulating basal adenosine levels. It is this action of ADK on the basal adenosine tone that is permissive to seizure activity, and, by extension, other forms of activity-dependent neuronal activity such as synaptic plasticity.

Postictal serum nucleotidases activities in patients with epilepsy

Adenosine, a potent anticonvulsant, can be produced in the body by the hydrolysis of adenine nucleotides through the action of ecto- or soluble nucleotidases. Changes in nucleotide hydrolysis occur after pentylenetetrazol-induced epileptic events. We evaluated serum ATP, ADP and AMP hydrolysis rates and soluble nucleotide phosphodiesterase (PDEase) activity at 5, 10, 15, 30 and 60 min, and 12h following an epileptic event. Fifteen patients (seven female, eight male; mean age 15.5 years) were included in the study. The type of seizure was generalized in four patients and was localization related in the remaining 11. There were no differences in adenine nucleotide hydrolysis rates between patients and healthy subjects in the interictal stage. In comparison with controls, ATP, ADP and AMP hydrolysis rates were significantly increased at 5 min (53+/-1.4%, 79.2+/-2.8% and 37.0+/-2.6%, respectively) and up to 30 min following the epileptic event. In contrast to ADP and AMP, ATP hydrolysis remained significantly increased at 60 min (71.4+/-1.6%), returning to the basal level after 12h. Serum PDEase activity was also significantly higher in the patients than in healthy subjects, peaking at 15 min (61+/-2.9%) and remaining significantly increased up to 60 min (4.6+/-1.2%) following the epileptic episode. Globally, the variations in the postictal serum ADP hydrolysis rate almost overlapped those of AMP hydrolysis, whereas changes in the ATP hydrolysis rate overlapped those of PDEase activity. The clinical significance of this elevation in postictal soluble serum nucleotidase activity remains to be clarified. However, it is possible to hypothesize that the higher nucleotidase activity might play a role in the modulation of epileptic events.

Adenosine receptors and the central nervous system

The adenosine receptors (ARs) in the nervous system act as a kind of "go-between" to regulate the release of neurotransmitters (this includes all known neurotransmitters) and the action of neuromodulators (e.g., neuropeptides, neurotrophic factors). Receptor-receptor interactions and AR-transporter interplay occur as part of the adenosine's attempt to control synaptic transmission. A(2A)ARs are more abundant in the striatum and A(1)ARs in the hippocampus, but both receptors interfere with the efficiency and plasticity-regulated synaptic transmission in most brain areas. The omnipresence of adenosine and A(2A) and A(1) ARs in all nervous system cells (neurons and glia), together with the intensive release of adenosine following insults, makes adenosine a kind of "maestro" of the tripartite synapse in the homeostatic coordination of the brain function. Under physiological conditions, both A(2A) and A(1) ARs play an important role in sleep and arousal, cognition, memory and learning, whereas under pathological conditions (e.g., Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke, epilepsy, drug addiction, pain, schizophrenia, depression), ARs operate a time/circumstance window where in some circumstances A(1)AR agonists may predominate as early neuroprotectors, and in other circumstances A(2A)AR antagonists may alter the outcomes of some of the pathological deficiencies. In some circumstances, and depending on the therapeutic window, the use of A(2A)AR agonists may be initially beneficial; however, at later time points, the use of A(2A)AR antagonists proved beneficial in several pathologies. Since selective ligands for A(1) and A(2A) ARs are now entering clinical trials, the time has come to determine the role of these receptors in neurological and psychiatric diseases and identify therapies that will alter the outcomes of these diseases, therefore providing a hopeful future for the patients who suffer from these diseases.

Silk polymer-based adenosine release: therapeutic potential for epilepsy

Adenosine augmentation therapies (AAT) make rational use of the brain's own adenosine-based seizure control system and hold promise for the therapy of refractory epilepsy. In an effort to develop an AAT compatible with future clinical application, we developed a novel silk protein-based release system for adenosine. Adenosine releasing brain implants with target release doses of 0, 40, 200, and 1000ng adenosine per day were prepared by embedding adenosine containing microspheres into nanofilm-coated silk fibroin scaffolds. In vitro, the respective polymers released 0, 33.4, 170.5, and 819.0ng adenosine per day over 14 days. The therapeutic potential of the implants was validated in a dose-response study in the rat model of kindling epileptogenesis. Four days prior to the onset of kindling, adenosine releasing polymers were implanted into the infrahippocampal cleft and progressive acquisition of kindled seizures was monitored over a total of 48 stimulations. We document a dose-dependent retardation of seizure acquisition. In recipients of polymers releasing 819ng adenosine per day, kindling epileptogenesis was delayed by one week corresponding to 18 kindling stimulations. Histological analysis of brain samples confirmed the correct location of implants and electrodes. We conclude that silk-based delivery of around 1000ng adenosine per day is a safe and efficient strategy to suppress seizures.

Gene therapy in epilepsy

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

Are purines mediators of the anticonvulsant/neuroprotective effects of ketogenic diets?

Abnormal neuronal signaling caused by metabolic changes characterizes several neurological disorders, and in some instances metabolic interventions provide therapeutic benefits. Indeed, altering metabolism either by fasting or by maintaining a low-carbohydrate (ketogenic) diet might reduce epileptic seizures and offer neuroprotection in part because the diet increases mitochondrial biogenesis and brain energy levels. Here we focus on a novel hypothesis that a ketogenic diet-induced change in energy metabolism increases levels of ATP and adenosine, purines that are critically involved in neuron-glia interactions, neuromodulation and synaptic plasticity. Enhancing brain bioenergetics (ATP) and increasing levels of adenosine, an endogenous anticonvulsant and neuroprotective molecule, might help with understanding and treating a variety of neurological disorders.

Evidence for the involvement of the adenosine A(2A) receptor in the lowered susceptibility to pentylenetetrazol-induced seizures produced in mice by long-term treatment with caffeine

Long-term caffeine intake has been reported to decrease the susceptibility to convulsants in mice. Occurrence of seizures following long-term oral administration of caffeine (0.3g/l) was investigated using adenosine A(2A) receptor knockout (A(2A)R KO) and control (A(2A)R WT) mice. Clonic seizures induced by acute pentylenetetrazol (PTZ, 50mg/kg i.p.) were significantly attenuated in adenosine A(2A)R KO mice drinking only water and reduced by a 14-day caffeine treatment in adenosine A(2A)R WT mice. In addition we showed a protecting effect of a 21-day caffeine treatment in A(2A)R WT mice against kindled seizures induced by PTZ in an increasing dose schedule. Summing up, these protective effects against PTZ-induced seizures occurring when adenosine A(2A)R is absent or chronically blocked by a relevant dose of caffeine may be related to a decreased neuronal excitability.

Adenosine kinase is a target for the prediction and prevention of epileptogenesis in mice

Astrogliosis is a pathological hallmark of the epileptic brain. The identification of mechanisms that link astrogliosis to neuronal dysfunction in epilepsy may provide new avenues for therapeutic intervention. Here we show that astrocyte-expressed adenosine kinase (ADK), a key negative regulator of the brain inhibitory molecule adenosine, is a potential predictor and modulator of epileptogenesis. In a mouse model of focal epileptogenesis, in which astrogliosis is restricted to the CA3 region of the hippocampus, we demonstrate that upregulation of ADK and spontaneous focal electroencephalographic seizures were both restricted to the affected CA3. Furthermore, spontaneous seizures in CA3 were mimicked in transgenic mice by overexpression of ADK in this brain region, implying that overexpression of ADK without astrogliosis is sufficient to cause seizures. Conversely, after pharmacological induction of an otherwise epileptogenesis-precipitating acute brain injury, transgenic mice with reduced forebrain ADK were resistant to subsequent epileptogenesis. Likewise, ADK-deficient ES cell-derived brain implants suppressed astrogliosis, upregulation of ADK, and spontaneous seizures in WT mice when implanted after the epileptogenesis-precipitating brain injury. Our findings suggest that astrocyte-based ADK provides a critical link between astrogliosis and neuronal dysfunction in epilepsy.

The adenosine kinase hypothesis of epileptogenesis

Current therapies for epilepsy are largely symptomatic and do not affect the underlying mechanisms of disease progression, i.e. epileptogenesis. Given the large percentage of pharmacoresistant chronic epilepsies, novel approaches are needed to understand and modify the underlying pathogenetic mechanisms. Although different types of brain injury (e.g. status epilepticus, traumatic brain injury, stroke) can trigger epileptogenesis, astrogliosis appears to be a homotypic response and hallmark of epilepsy. Indeed, recent findings indicate that epilepsy might be a disease of astrocyte dysfunction. This review focuses on the inhibitory neuromodulator and endogenous anticonvulsant adenosine, which is largely regulated by astrocytes and its key metabolic enzyme adenosine kinase (ADK). Recent findings support the "ADK hypothesis of epileptogenesis": (i) Mouse models of epileptogenesis suggest a sequence of events leading from initial downregulation of ADK and elevation of ambient adenosine as an acute protective response, to changes in astrocytic adenosine receptor expression, to astrocyte proliferation and hypertrophy (i.e. astrogliosis), to consequential overexpression of ADK, reduced adenosine and - finally - to spontaneous focal seizure activity restricted to regions of astrogliotic overexpression of ADK. (ii) Transgenic mice overexpressing ADK display increased sensitivity to brain injury and seizures. (iii) Inhibition of ADK prevents seizures in a mouse model of pharmacoresistant epilepsy. (iv) Intrahippocampal implants of stem cells engineered to lack ADK prevent epileptogenesis. Thus, ADK emerges both as a diagnostic marker to predict, as well as a prime therapeutic target to prevent, epileptogenesis.

Adenosine as a neuromodulator in neurological diseases

Adenosine is a modulator of brain function uniquely positioned to integrate excitatory and inhibitory neurotransmission. The past few years brought a wealth of new data fostering our understanding of how the adenosine system is involved in the pathogenesis of neurological diseases. Thus, dysregulation of the adenosine system is implicated in epileptogenesis and cell therapies have been developed to locally augment adenosine in an approach to prevent seizures. While activation of inhibitory adenosine A(1) receptors is beneficial in epilepsy, chronic pain and cerebral ischemia, inhibition of facilitatory A(2A) receptors has profound neuroprotective effects, which are currently exploited in clinical trials in Parkinson's disease. A new era of adenosine-based therapies has begun, with the prospect to cover a wide range of neurological diseases.

Lentiviral RNAi-induced downregulation of adenosine kinase in human mesenchymal stem cell grafts: a novel perspective for seizure control

Cell therapies based on focal delivery of the inhibitory neuromodulator adenosine were previously shown to provide potent seizure suppression in animal models of epilepsy. However, hitherto used therapeutic cells were derived from rodents and thus not suitable for clinical applications. Autologous patient-derived adenosine-releasing cell implants would constitute a major therapeutic advance to avoid both xenotransplantation and immunosuppression. Here we describe a novel approach based on lentiviral RNAi mediated downregulation of adenosine kinase (ADK), the major adenosine-removing enzyme, in human mesenchymal stem cells (hMSCs), which would be compatible with autologous cell grafting in patients. Following lentiviral transduction of hMSCs with anti-ADK miRNA expression cassettes we demonstrate up to 80% downregulation of ADK and a concentration of 8.5 ng adenosine per ml of medium after incubating 10(5) cells for 8 h. hMSCs with a knockdown of ADK or cells expressing a scrambled control sequence were transplanted into hippocampi of mice 1 week prior to the intraamygdaloid injection of kainic acid (KA). While mice with control implants expressing a scrambled miRNA sequence or sham treated control animals were characterized by KA-induced status epilepticus and subsequent CA3 neuronal cell loss, animals with therapeutic ADK knockdown implants displayed a 35% reduction in seizure duration and 65% reduction in CA3 neuronal cell loss, when analyzed 24 h after KA-injection. We conclude that lentiviral expression of anti-ADK miRNA constitutes a versatile tool to generate therapeutically effective adenosine releasing hMSCs, thus representing a model system to generate patient identical autologous adult stem cell grafts.