Abstracts

Rationale: Neuroinflammation is a major pathological factor in epilepsy. It is induced by experimental epileptogenic injuries and seizures as well as in human pharmacoresistant epilepsy. Neuroinflammation contributes to acute and chronic seizures, and possibly to epileptogenesis, likely because the diseased brain lacks efficient anti-inflammatory mechanisms for limiting its extent and duration. Resolution of inflammation is a highly coordinated process chiefly controlled by endogenous pro-resolving lipids and peptides. Our hypothesis is that neuroinflammation is inefficiently controlled by pro-resolving mediators, such as ResolvinD1 (RvD1), LipoxinA4 (LXA4), AnnexinA1 (AnxA1) and their receptors ChemR23 and LXA4 Receptor (ALXR). We studied, therefore, the expression of pro-resolving molecules during epileptogenesis induced by status epilepticus (SE) in mice, and validated the presence of some molecules in hippocampi from patients with mesial temporal lobe epilepsy (TLE). The final goal is to limit the pathologic consequences of the inflammatory response by boosting its resolution with pharmacological interventions.Methods: SE was induced in adult male mice by intra-amygdala kainate or systemic pilocarpine. Mice were sacrified 2 h, 24 h, 72 h and 1 week after SE. The pro-inflammatory cytokines IL-1β and TNF-α, ChemR23 and ALXR, and key biosynthetic enzymes of pro-resolving lipids LOX-5 and LOX-15 were analyzed by RT-PCR and immunohistochemistry in the hippocampus of SE and sham mice. Some molecules were analyzed also in the hippocampus of TLE patients and autopsy controls. BML111, a LXA4 stable analogue, was injected intracerebroventricularly in mice after kainate-induced SE, and its effect was assessed by immunohistochemistry on IL-1β and TNF-α expression in the hippocampus, 48 h post-SE.Results: ChemR23, ALXR and AnxA1 protein expression was limited to pyramidal neurons and hilar interneurons in sham mice. 72 h after SE, they were induced in activated astrocytes. LOX-5 and LOX-15 mRNA levels were also up-regulated 72 h after SE in the hippocampus of mice and of TLE patients. These protein alterations after SE were similar both in kainate and pilocarpine mice, thus excluding model-specific effects. Pro-resolving molecules were induced with a delayed time-course compared to inflammatory cytokines. Treatment with BML111 virtually abolished the SE-induced increase in IL-1β and TNF-α expression.Conclusions: Pro-resolving mediators are induced after SE likely reflecting seizure-mediated up-regulation. These molecules are also induced in TLE patients suggesting that pro-resolving signaling activation occurs in pharmacoresistant epilepsy. Neuroinflammation following SE precedes the up-regulation of pro-resolving mechanisms denoting a delayed activation of resolution mechanisms during epileptogenesis. Treatment with a drug mimicking LXA4 strongly reduces neuroinflammation. This evidence reveals that pharmacological intervention with pro-resolving drugs reduces neuroinflammation, thus supporting further studies on their potential anti-epileptogenic actions.