Abstracts

Rationale: Experimental evidence shows that Interleukin-1ß (IL-1ß), a pro-inflammatory cytokine, can initiate neuronal responses altering synaptic plasticity and excitatory/inhibitory balance. In rodents, pre-exposure to IL-1ß exacerbates seizures, and the pro-convulsive effects are dependent on IL-1ß receptor 1 (IL-1R1) binding, activation of the tyrosine kinase Src and increased phosphorylation of NMDA receptor subunit GluN2B. However, the precise effects of IL-1ß on network activity in human chronic epilepsy remains unclear. Here, we used combined ex vivo electrophysiology, biochemical analysis and immunohistochemistry to investigate the effects of exogenous IL-1ß on human epileptogenic networks, and begin to elucidate the mechanisms involved. Methods: Tissue samples were obtained at the NYU Medical Center for treatment of pharmaco-resistant epilepsy. Matched autopsy control brain samples were obtained from the NIH NeuroBioBank. The study was approved by the local Institutional Review Board. After removal, the tissue was placed in cold oxygenated artificial CSF and then 450µm slices were cut and placed in an interface recording chamber continuously perfused with oxygenated solution. Extracellular local field potential recordings were performed and the recording electrode was placed within cortical layers III or V. Slices were perfused with artificial CSF to record baseline activity, and subsequently treated with human recombinant IL-1ß (10 ng/ml). Once the IL-1ß activity was induced, the effects of IL-1 receptor antagonist IL-1Ra (5µg/ml), the Src inhibitor PP2 (5-10µM), or the specific GluN2B blocker Ifenprodil (10µM) were tested. The duration of epileptiform activity was measured before and after each drug application. Additional frozen and fixed samples were used for Western blotting and immunohistochemistry to determine the baseline expression levels and cellular localization of IL-1ß, IL-1Ra and IL-1R1. The statistical analysis was performed using t-tests. Results: Acute IL-1ß bath application induced prolonged rhythmic epileptiform discharges in all slices (p<0.0001; n=23). Epileptiform activities induced by IL-1ß were blocked by IL-1Ra (p=0.026; n=5), PP2 (p=0.005; n=5) and Ifenprodil (p=0.032; n=5). Western blot analysis showed increased IL-1ß (p<0.0001; n=16) and IL-1R1 (p<0.05; n=5) expression, and decreased IL1Ra levels (p<0.01; n=8) in epilepsy samples, regardless of the underlying neuropathology. IL-1ß was expressed mainly in astrocytes, while IL-1R1 was mostly present in neurons. Conclusions: These results provide the first direct evidence that IL-1ß has a potent pro-convulsive effect in human chronic epilepsy tissue. These effects are mediated by IL-1R1, and involve Src activation and enhancement of NMDAR function. Our expression studies are consistent with chronic activation of IL-1ß signaling. All together, these data suggests that patients suffering from therapy resistant epilepsy may benefit from novel therapies that suppress IL-1ß release, or directly block neuronal cytokine signaling. Funding: NYU FACES (Finding a Cure for Epilepsy); University Research Foundation