Mitigating Post-Traumatic Epileptogenesis by Enhancing Synaptic Glutamate Transport via Long-Term Non-Bactericidal Beta-Lactam Administration

PROJECT SUMMARY Traumatic brain injury (TBI) often leads to epilepsy with a delay of weeks to months after the initial trauma. Immediately following and for days to weeks after TBI, increased extracellular glutamate leads to hyperexcitation of neurons, and to neuronal injury. These effects are exacerbated by post-traumatic downregulation of glutamate transporter 1 (GLT-1), the protein responsible for synaptic glutamate clearance. Long-term, post-TBI glutamate excitotoxicity leads to a progressive loss of vulnerable inhibitory interneurons and GABAergic intracortical inhibition, and contributes to a range of chronic post-TBI symptoms, that include post-traumatic epilepsy (PTE). We identified that short-term treatment with the injectable beta-lactam ceftriaxone (CRO) increases GLT-1 expression and mitigates post-TBI neuronal death and seizures in a rat acquired epilepsy model, albeit incompletely. CRO-mediated GLT-1 rescue does not persist beyond cessation of treatment, while the TBI- induced depression of the gene that encodes for GLT-1 persists up to 6 weeks after TBI. Since CRO and similar injectable antibiotics cannot be given for weeks to months without complications, a sustained non-antibiotic treatment that can be administered safely and conveniently is highly desirable. The atypical non-bactericidal beta-lactam clavulanic acid (CLAV) also increases GLT-1 expression and protects against glutamate-mediated damage in animal models. This well-tolerated, orally available drug can potentially serve as a mainstay of prolonged post-TBI GLT-1 upregulation strategies aimed at sustained neuroprotection and anti-epileptogenesis. However, essential questions pertaining to CLAV mechanism and efficacy should be addressed in the preclinical setting. Based on prior work showing that CRO modulates GLT-1 after TBI, and published data showing CLAV does the same in other animal models, we propose a set of exploratory experiments aimed to (1) determine the dose-response relationship between CLAV and GLT-1 expression following TBI, (2) test whether long-term beta- lactam treatment mitigates TBI-induced long-term GLT-1 depression, oxidative stress, and inhibitory interneuronal death, (3) test whether long-term beta-lactam treatment prevents or mitigates progressive, post- TBI decrease in cortical inhibition, seizure threshold, and PTE. Given that no intervention targeting post-TBI epileptogenesis is available, our proposed experiments will be the first step toward a novel treatment. Despite the strong implication of glutamate-mediated changes in post-traumatic epileptogenesis, there is presently no proven long-term clinical method to clear excessive glutamate from the extracellular space after injury. Our proposal combines established basic science methods with a novel application of CLAV treatment as an antiepileptogenic intervention which can be administered acutely after TBI. As CLAV is already FDA approved for human use, positive data from the proposed studies may be rapidly translated to further development of this post-TBI treatment strategy, and to human trials. Beyond TBI, enhancement of glutamate transport may also prove useful following various other forms of brain injury.