Abstracts

Rationale: Organophosphate (OP) chemical weapons and pesticides account for over 300,000 casualties worldwide per year, and significantly greater morbidity. OPs cause acute neurotoxicity via inhibition of acetylcholinesterase, which can cause cholinergic crisis, status epilepticus (SE), and death. Current medical countermeasures reduce mortality; however, they are insufficient to prevent OP-induced epileptogenesis. One explanation derived from recent literature linking neuroinflammation to epileptogenesis is that current standard of care therapeutics for acute OP intoxication do not mitigate the robust and persistent neuroinflammatory response triggered by acute OP poisoning.  Here, we test this hypothesis.

Methods: We used a rat model of acute intoxication with the OP, DFP, to assess whether the soluble epoxide hydrolase (sEH) inhibitor, TPPU, which reduces pro-inflammatory lipids, mitigates spontaneous recurrent seizures (SRS). Adult male Sprague-Dawley rats were exposed to DFP (3.25-3.75 mg/kg, s.c) and scored for seizure severity using seizure behavior criteria for 4 h following DFP exposure. Animals were assigned to either short-term or long-term cohorts, wherein short-term animals received daily i.p. injections of TPPU (1 mg/kg, i.p.) or an equal volume of vehicle (VEH, 20% polyethylene glycol 400 in sterile saline) starting at 1 d post-exposure (DPE) for 7 d. Long-term animals received equivalent doses of TPPU starting at 21 DPE when SRS had been established and were continuously monitored for seizure burden 24 h/d via implanted EEG telemetry until 35 DPE.

Results: DFP-intoxicated rats treated with TPPU for 7 d beginning at 24 h post-DFP exposure exhibited a significant time-dependent reduction in Iba-1 immunoreactive cells that were also immunoreactive for CD68 in the CA1 and dentate gyrus region of the hippocampus, indicating that TPPU decreased early neuroinflammatory responses. DFP-intoxicated rats treated with TPPU at 21 DPE, after SRS had been established, exhibited a significant reduction in seizure frequency for the duration of the 14 d treatment.

Conclusions: Our findings suggest that acute administration of the sEH inhibitor, TPPU, modulates early neuroinflammatory responses to OP-induced seizures while delayed treatment after SRS has been established mitigates seizure frequency. These findings support the hypothesis that neuroinflammation is a pathogenic mechanism linking acute and chronic effects of acute OP intoxication; however, it remains to be determined whether TPPU effects on neuroinflammation mediate the effects of TPPU on SRS, and whether mitigation of acute neuroinflammatory responses is sufficient to prevent OP-induced epileptogenesis. Addressing these questions are the focus of ongoing studies. Nonetheless, these observations support further studies of TPPU as a potential antiepileptic and neuroprotective therapeutic.

Funding: Supported by the NIH CounterACT Program (grant # NS079202)