Sulfasalazine decreases astrogliosis-mediated seizure burden.

OBJECTIVE: Previously, we reported that inhibition of the astrocytic cystine/glutamate antiporter system xc- (SXC), using sulfasalazine (SAS), decreased evoked excitatory signaling in three distinct hyperexcitability models ex vivo. The current study expands on this work by evaluating the in vivo efficacy of SAS in decreasing astrogliosis-mediated seizure burden seen in the beta-1 integrin knockout (B1KO) model. METHODS: Video-EEG (electroencephalography) monitoring (24/7) was obtained using Biopac EEG acquisition hardware and software. EEG spectral analysis was performed using MATLAB. SAS was used at an equivalence of doses taken by Crohn's disease patients. Whole-cell patch-clamp recordings were made from cortical layer 2/3 pyramidal neurons. RESULTS: We report that 100% of B1KO mice that underwent 24/7 video-EEG monitoring developed spontaneous recurrent seizures and that intraperitoneal administration of SAS significantly reduced seizure frequency in B1KOs compared to B1KOs receiving sham saline. Spectral analysis found an acute reduction in EEG power following SAS treatment in B1KOs; however, this effect was not observed in nonepileptic control mice receiving SAS. Finally, whole-cell recordings from SXC knockout mice had hyperpolarized neurons and SXC-B1 double knockouts fired significantly less action potentials in response to current injection compared to B1KOs with SXC. SIGNIFICANCE: To devise effective strategies in finding relief for one-in-three patients with epilepsy who experience drug-resistant epilepsy we must continue to explore the mechanisms regulating glutamate homeostasis. This study explored the efficacy of targeting an astrocytic glutamate antiporter, SXC, as a novel antiepileptic drug (AED) target and further characterized a unique mouse model in which chronic astrogliosis is sufficient to induce spontaneous seizures and epilepsy. These findings may serve as a foundation to further assess the potential for SAS or inform the development of more potent and specific compounds that target SXC as a novel treatment for epilepsy.

Dysregulation of Ambient Glutamate and Glutamate Receptors in Epilepsy: An Astrocytic Perspective.

Given the important functions that glutamate serves in excitatory neurotransmission, understanding the regulation of glutamate in physiological and pathological states is critical to devising novel therapies to treat epilepsy. Exclusive expression of pyruvate carboxylase and glutamine synthetase in astrocytes positions astrocytes as essential regulators of glutamate in the central nervous system (CNS). Additionally, astrocytes can significantly alter the volume of the extracellular space (ECS) in the CNS due to their expression of the bi-directional water channel, aquaporin-4, which are enriched at perivascular endfeet. Rapid ECS shrinkage has been observed following epileptiform activity and can inherently concentrate ions and neurotransmitters including glutamate. This review highlights our emerging knowledge on the various potential contributions of astrocytes to epilepsy, particularly supporting the notion that astrocytes may be involved in seizure initiation via failure of homeostatic responses that lead to increased ambient glutamate. We also review the mechanisms whereby ambient glutamate can influence neuronal excitability, including via generation of the glutamate receptor subunit GluN2B-mediated slow inward currents, as well as indirectly affect neuronal excitability via actions on metabotropic glutamate receptors that can potentiate GluN2B currents and influence neuronal glutamate release probabilities. Additionally, we discuss evidence for upregulation of System x c - , a cystine/glutamate antiporter expressed on astrocytes, in epileptic tissue and changes in expression patterns of glutamate receptors.

Sulfasalazine decreases mouse cortical hyperexcitability.

OBJECTIVE: Currently prescribed antiepileptic drugs (AEDs) are ineffective in treating approximately 30% of epilepsy patients. Sulfasalazine (SAS) is an US Food and Drug Administration (FDA)-approved drug for the treatment of Crohn disease that has been shown to inhibit the cystine/glutamate antiporter system xc- (SXC) and decrease tumor-associated seizures. This study evaluates the effect of SAS on distinct pharmacologically induced network excitability and determines whether it can further decrease hyperexcitability when administered with currently prescribed AEDs. METHODS: Using in vitro cortical mouse brain slices, whole-cell patch-clamp recordings were made from layer 2/3 pyramidal neurons. Epileptiform activity was induced with bicuculline (bic), 4-aminopyridine (4-AP) and magnesium-free (Mg2+ -free) solution to determine the effect of SAS on epileptiform events. In addition, voltage-sensitive dye (VSD) recordings were performed to characterize the effect of SAS on the spatiotemporal spread of hyperexcitable network activity and compared to currently prescribed AEDs. RESULTS: SAS decreased evoked excitatory postsynaptic currents (eEPSCs) and increased the decay kinetics of evoked inhibitory postsynaptic currents (eIPSCs) in layer 2/3 pyramidal neurons. Although application of SAS to bic and Mg2+ -free-induced epileptiform activity caused a decrease in the duration of epileptiform events, SAS completely blocked 4-AP-induced epileptiform events. In VSD recordings, SAS decreased VSD optical signals induced by 4-AP. Co-application of SAS with the AED topiramate (TPM) caused a significantly further decrease in the spatiotemporal spread of VSD optical signals. SIGNIFICANCE: Taken together this study provides evidence that inhibition of SXC by SAS can decrease network hyperexcitability induced by three distinct pharmacologic agents in the superficial layers of the cortex. Furthermore, SAS provided additional suppression of 4-AP-induced network activity when administered with the currently prescribed AED TPM. These findings may serve as a foundation to assess the potential for SAS or other compounds that selectively target SXC as an adjuvant treatment for epilepsy.