Abstracts

Rationale: Accumulating evidence suggests a positive feedback cycle between brain inflammation and epileptogenesis. Recurrent seizures lead to activated immune responses which in turn further increase neuronal excitability and induce BBB breakdown. In this study, we utilized biocompatible nanoparticles (NP) detectible by optical imaging to target activated macrophage-like cells in epileptogenic brain tissue, taking advantage of local immune cell activation and BBB disruption. Methods: Polylactic acid (PLA)-based NP were prepared by a modified emulsification-solvent evaporation method with the incorporation of oleate-coated magnetite nanocrystals. In vitro NP uptake was assessed using RAW 246.7 cells. The in vivo cellular NP distribution was evaluated using the lithium-pilocarpine model of temporal lobe epilepsy. Three hr, 6, hr, 24 hr and 7 d after intravenous injections of the NP, brains were harvested and analyzed by immunohistochemistry. For each rat, the NP were counted in hippocampal CA1 and CA3, in twelve high power fields (HPF) per brain area. Results: The NP were rapidly and completely uptaken by RAW 246.7 cells, with T₅₀ of 0.23 ± 0.02 hr and E_max of 99.7% ± 2.6%. In vivo, the NP were detected in the brains of rats with spontaneous seizures, but not in controls. In rats in which spontaneous seizures were induced, the NP accumulated almost exclusively in macrophages/microglia (Figure 1), with greater accumulation in CA1 at 3 hr, 6 hr and 24 hr, compared to 7 days (3.9 ± 3.6, 3.8 ± 2.3 and ± 3.6 ± 2.0 vs. 1.2 ± 1.4 NP/HPF, respectively; P<0.05), but no significant time course differences in the CA3 (0.9 ± 1.3, 0.7 ± 0.7, 1.5 ± 1.1 and 0.9 ± 1.2 NP/HPF at 3 hr 6 hr, 24 hr, and 7 d, respectively). Conclusions: We established a proof of concept for the ability to deliver NP to macrophages/microglia in epileptogenic brain tissue. Our proposed traceable NP, uptaken by circulating or resident phagocytic cells, could contribute to the proper localization of epileptic foci. In addition, this system may be utilized for drug delivery and contribute to elucidating the immune contribution to the development and persistence of epileptic seizures. This study was supported by the Israeli Ministry of Economy, the Drexel University-Hebrew University Translational Research Partnership, and the The Prusiner-Abramsky Research Awards in Clinical and Basic Neuroscience.