Abstracts

Rationale: Traumatic brain injury (TBI) is the third most common cause of all epilepsies. TBI induces a neuroinflammatory response that can initiate epileptogenesis, a pathological process that leads to the development of epilepsy. The etiopathology and mechanisms of post-traumatic epilepsy (PTE) are either unknown or poorly understood, which makes treatment challenging. Although anti-epileptic drugs are used as preventive strategies, their efficacy in PTE remains controversial. Reports have indicated that opioid antagonists reduce inflammation after brain injury. Recently, we evaluated anti-convulsive role of Naltrexone (NTX), a mu-opioid receptor (MOR) antagonist, in a pentylenetetrazole (PTZ)-induced model of epilepsy. Mice pre-treated with NTX were resistant to PTZ-induced seizures suggesting a role of MOR in seizures. Therefore, we hypothesized that modulating MOR, with NTX, after TBI can prevent epileptogenesis.

Methods: A diffused brain injury, by free fall weight-drop, was induced on a four-week-old male C57BL/6J mice. Electrodes were implanted with a telemetry device at one day post-injury (dpi). A sub-convulsive dose of PTZ (30 mg/kg, i.p.) was administered at 3 dpi, and behavioral seizures were assessed for an hour. Naltrexone (40 mg/kg, sq) or vehicle treatment was initiated 2 h post-PTZ (twice daily for three days followed by daily for the next four days). The mice were vEEG monitored continuously for seven days and then intermittently for three months. All the animals were euthanized with sodium pentobarbital (100 mg/kg, i.p.). The brain tissues and serum were harvested and processed for various proteomic and immunohistochemical (IHC) analyses.

Results: Three months of vEEG study revealed that 75% of the animals with brain injury developed PTE, whereas none of the NTX treated mice developed epilepsy. The number of epileptiform discharges were also reduced in the NTX mice compared to the vehicle-treated group. IHC analysis of brain sections revealed an increase in gliosis in the cortex and hippocampus of injured mice. Neurodegeneration (FJB+NeuN positive cells) was greater in both the brain regions at 7 d post-injury in the vehicle-treated group when compared to NTX group. Western blot assays revealed enhanced MOR, phospho-p38 MAPK and nitroxidative stress markers (gp91^phox, 3-NT and iNOS) in the brain of injured mice. These biomarkers were significantly reduced in the NTX treated mice. The Quantibody 45-multiplex array also revealed a significant reduction in the proinflammatory cytokines and increase in anti-inflammatory cytokines (IL-4 and IL-10) in the serum of NTX treated mice.

Conclusions: Naltrexone treatment suppresses TBI-induced neuroinflammation, neurodegeneration, epileptiform discharges, and spontaneous recurrent seizures. These findings suggest that Naltrexone can be developed as a potential disease-modifying agent to prevent the development and progression of PTE.

Funding: Please list any funding that was received in support of this abstract.: The work was supported by NIH 5R01NS098590 and Tross Family grant to Dr. Alexander Bassuk.