Epileptic seizures are a common and poorly understood co-morbidity for individuals with primary brain tumors. To investigate peritumoral seizure etiology, we implanted patient-derived glioma cells into scid mice. Within 14–18 days, glioma-bearing animals developed spontaneous, recurring abnormal EEG events consistent with epileptic activity that progressed over time. Acute brain slices from these animals showed significant glutamate release from the tumor mediated by the system xc− cystine/glutamate transporter. Biophysical and optical recordings showed glutamatergic epileptiform hyperexcitability that spread into adjacent brain. Glutamate release from the tumor and the ensuing hyperexcitability were inhibited by sulfasalazine (Azulfidine), an FDA approved drug that blocks system xc−. Acute administration of sulfasalazine at concentrations equivalent to that used by those with Crohn’s disease reduced epileptic event frequency in tumor-bearing mice. Sulfasalazine should be considered as an adjuvant treatment to ameliorate peritumoral seizures associated with glioma.

Glioma is the most common malignant primary brain tumor. Their rapid growth is aided by tumor-mediated release of glutamate, creating peritumoral excitotoxic cell death and vacating space for tumor expansion. Glioma glutamate release may also be responsible for seizures, which complicate the clinical course for many patients and are often the presenting symptom. A hypothesized glutamate release pathway is the cystine/glutamate transporter System xc− (SXC), responsible for the cellular synthesis of glutathione. However, the relationship of SXC-mediated glutamate release, seizures, and tumor growth remains unclear. Probing expression of SLC7A11/xCT, the catalytic subunit of SXC, in patient tissue and tissues propagated in mice, we found that approximately 50% of patient tumors have elevated SLC7A11 expression. Compared with tumors lacking this transporter, in vivo propagated and intracranially implanted SLC7A11-expressing tumors grew faster, produced pronounced peritumoral glutamate excitotoxicity, induced seizures, and shortened overall survival. In agreement with animal data, increased SLC7A11 expression predicted shorter patient survival according to annotated genomic data in the REMBRANDT database. In a clinical pilot study we used Magnetic Resonance Spectroscopy (MRS) to determine SXC-mediated glutamate release by measuring acute changes in glutamate after administration of the FDA-approved SXC inhibitor, sulfasalazine. In 9 glioma patients with biopsy-confirmed expression of SXC, we found that its expression positively correlates with glutamate release, which is acutely inhibited with oral sulfasalazine. These data suggest that SXC is the major pathway for glutamate release from gliomas and that SLC7A11 expression predicts accelerated growth and peritumoral seizures.

Epilepsy is one of the most common chronic neurologic diseases, yet approximately one-third of affected patients do not respond to anticonvulsive drugs that target neurons or neuronal circuits. Reactive astrocytes are commonly found in putative epileptic foci and have been hypothesized to be disease contributors because they lose essential homeostatic capabilities. However, since brain pathology induces astrocytes to become reactive, it is difficult to distinguish whether astrogliosis is a cause or a consequence of epileptogenesis. We now present a mouse model of genetically induced, widespread chronic astrogliosis after conditional deletion of ␤1-integrin (Itg␤1). In these mice, astrogliosis occurs in the absence of other pathologies and without BBB breach or significant inflammation. Electroencephalography with simultaneous video recording revealed that these mice develop spontaneous seizures during the first six postnatal weeks of life and brain slices show neuronal hyperexcitability. This was not observed in mice with neuronal-targeted ␤1-integrin deletion, supporting the hypothesis that astrogliosis is sufficient to induce epileptic seizures. Whole-cell patch-clamp recordings from astrocytes further suggest that the heightened excitability was associated with impaired astrocytic glutamate uptake. Moreover, the relative expression of the cation-chloride cotransporters (CCC) NKCC1 (Slc12a2) and KCC2 (Slc12a5), which are responsible for establishing the neuronal Cl Ϫ gradient that governs GABAergic inhibition were altered and the NKCC1 inhibitor bumetanide eliminated seizures in a subgroup of mice. These data suggest that a shift in the relative expression of neuronal NKCC1 and KCC2, similar to that observed in immature neurons during development, may contribute to astrogliosis-associated seizures.

Neuronal hyperexcitability occurs early in the pathogenesis of Alzheimer's disease (AD) and contributes to network dysfunction in AD patients. In other disorders with neuronal hyperexcitability, dysfunction in the dendrites often contributes, but dendritic excitability has not been directly examined in AD models. We used dendritic patch-clamp recordings to measure dendritic excitability in the CA1 region of the hippocampus. We found that dendrites, more so than somata, of hippocampal neurons were hyperexcitable in mice overexpressing A␤. This dendritic hyperexcitability was associated with depletion of Kv4.2, a dendritic potassium channel important for regulating dendritic excitability and synaptic plasticity. The antiepileptic drug, levetiracetam, blocked Kv4.2 depletion. Tau was required, as crossing with tau knock-out mice also prevented both Kv4.2 depletion and dendritic hyperexcitability. Dendritic hyperexcitability induced by Kv4.2 deficiency exacerbated behavioral deficits and increased epileptiform activity in hAPP mice. We conclude that increased dendritic excitability, associated with changes in dendritic ion channels including Kv4.2, may contribute to neuronal dysfunction in early stages AD.

Seizures frequently accompany gliomas and often escalate to peritumoral epilepsy. Previous work revealed the importance of tumor-derived excitatory glutamate (Glu) release mediated by the cystine-glutamate transporter (SXC) in epileptogenesis. We now show a novel contribution of GABAergic disinhibition to disease pathophysiology. In a validated mouse glioma model, we found that peritumoral parvalbumin-positive GABAergic inhibitory interneurons are significantly reduced, corresponding with deficits in spontaneous and evoked inhibitory neurotransmission. Most remaining peritumoral neurons exhibit elevated intracellular Cl− concentration ([Cl−]i) and consequently depolarizing, excitatory GABA responses. In these neurons, the plasmalemmal expression of KCC2, which establishes the low [Cl−]i required for GABAAR-mediated inhibition, is significantly decreased. Interestingly, reductions in inhibition are independent of Glu release, but the presence of both decreased inhibition and decreased SXC expression is required for epileptogenesis. We suggest GABAergic disinhibition renders peritumoral neuronal networks hyper-excitable and susceptible to seizures triggered by excitatory stimuli, and propose KCC2 as a therapeutic target.

Summary Purpose Patients with gliomas frequently present with seizures, but the factors associated with seizure development are still poorly understood. In this study, we assessed peritumoral synaptic network activity in a glioma animal model and tested the contribution of aberrant glutamate release from gliomas on glioma-associated epileptic network activity. Methods In vitro brain slices were made from glioma-implanted mice. Using extracellular field recordings, we analyzed peritumoral epileptiform activity induced by Mg2+-free medium in slices from tumor-bearing animals and sham-operated controls. We assessed the effect of sulfasalazine (SAS), a blocker of system xc− and glutamate release, on spontaneous and evoked activity in tumor-associated slices. Key Findings Tumor-associated cortical networks were hyperexcitable. The onset latency of Mg2+-free-induced epileptiform activity was significantly shorter in tumor-bearing slices, and the incidence of Mg2+-free-induced ictal-like events was higher. Block of glutamate release from system xc− decreased the response area of evoked activity and completely blocked Mg2+-free-induced ictal-like, but not interictal-like events. Significance Control of seizures in patients with gliomas is an essential component of clinical management; therefore, understanding the origin of seizures is vital. This work provides evidence that peritumoral synaptic network activity is disrupted by tumor masses resulting in network excitability. We show that blocking glutamate release via system xc− with SAS, a drug already approved by the US Food and Drug Administration (FDA), can inhibit Mg2+-free-induced ictal-like epileptiform events similar to other chemicals used to decrease seizure activity. We therefore suggest that further studies should consider SAS a promising agent to aid in the treatment of seizures associated with gliomas.

These contrasting illness narratives affect and shape the experiences, thoughts, and fears of patients and their carers in the last months of life. Palliative care offered by generalists or specialists should be provided more flexibly and equitably, responding to the varied concerns and needs of people with different advanced conditions.

Status epilepticus (SE) triggers abnormal expression of genes in the hippocampus, such as glutamate receptor subunit epsilon-2 (Grin2b/Nr2b) and brain-derived neurotrophic factor (Bdnf), that is thought to occur in temporal lobe epilepsy (TLE). We examined the underlying DNA methylation mechanisms and investigated whether these mechanisms contribute to the expression of these gene targets in the epileptic hippocampus. Experimental TLE was provoked by kainic acid-induced SE. Bisulfite sequencing analysis revealed increased Grin2b/Nr2b and decreased Bdnf DNA methylation levels that corresponded to decreased Grin2b/Nr2b and increased Bdnf mRNA and protein expression in the epileptic hippocampus. Blockade of DNA methyltransferase (DNMT) activity with zebularine decreased global DNA methylation levels and reduced Grin2b/Nr2b, but not Bdnf, DNA methylation levels. Interestingly, we found that DNMT blockade further decreased Grin2b/Nr2b mRNA expression whereas GRIN2B protein expression increased in the epileptic hippocampus, suggesting that a posttranscriptional mechanism may be involved. Using chromatin immunoprecipitation analysis we found that DNMT inhibition restored the decreases in AP2alpha transcription factor levels at the Grin2b/Nr2b promoter in the epileptic hippocampus. DNMT inhibition increased field excitatory postsynaptic potential in hippocampal slices isolated from epileptic rats. EEG monitoring confirmed that DNMT inhibition did not significantly alter disease course, but promoted the latency to seizure onset or SE. Thus, DNA methylation may be an early event triggered by SE that persists late into the epileptic hippocampus to contribute to gene expression changes in TLE.