Monocytes as carriers of magnetic nanoparticles for tracking inflammation in the epileptic rat brain

Background: Inflammation is a hallmark of epileptogenic brain tissue. Previously, we have shown that inflammation in epilepsy can be delineated using systemically-injected fluorescent and mag-netite-laden nanoparticles. Suggested mechanisms included distribution of free nanoparticles across a compromised blood-brain barrier or their transfer by monocytes that infiltrate the epileptic brain. Objective: In the current study, we evaluated monocytes as vehicles that deliver nanoparticles into the epileptic brain. We also assessed the effect of epilepsy on the systemic distribution of nanoparticle-loaded monocytes. Methods: The in vitro uptake of 300-nm nanoparticles labeled with magnetite and BODIPY (for optical imaging) was evaluated using rat monocytes and fluorescence detection. For in vivo studies we used the rat lithium-pilocarpine model of temporal lobe epilepsy. In vivo nanoparticle distribution was evaluated using immunohistochemistry. Results: 89% of nanoparticle loading into rat monocytes was accomplished within 8 hours, enabling overnight nanoparticle loading ex vivo. The dose-normalized distribution of nanoparticle-loaded monocytes into the hippocampal CA1 and dentate gyrus of rats with spontaneous seizures was 176-fold and 380-fold higher compared to the free nanoparticles (p<0.05). Seizures were associated with greater nanoparticle accumulation within the liver and the spleen (p<0.05). Conclusion: Nanoparticle-loaded monocytes are attracted to epileptogenic brain tissue and may be used for labeling or targeting it, while significantly reducing the systemic dose of potentially toxic compounds. The effect of seizures on monocyte biodistribution should be further explored to better understand the systemic effects of epilepsy.