Abstracts

Rationale: Chemical warfare nerve agents (CWNAs) are acetylcholinesterase (AChE) inhibitors that lead to pharmacoresistant status epilepticus (SE) and severe neuropathology when treatment is delayed. Some organophosphorus CWNAs such as soman also inhibit carboxylesterase (CaE), which acts as a bioscavenger to reduce the toxicity of soman. Unlike humans, rodents have plasma CaE activity. A novel humanized mouse strain (ES1-/-) was used in this study in which the gene expressing serum CaE was interrupted. This ES1-/-mouse strain might better model human soman exposure compared to wildtype rodents. A model of treatment of soman-exposed ES1-/- mice with standard medical countermeasures (atropine sulfate, an oxime [HI-6] and a benzodiazepine [midazolam]) was implemented to assess adjunct therapies for neuroprotective potential against soman exposure. We evaluated combination therapy of midazolam and the NMDA antagonist ketamine in male and female mice for efficacy against soman-induced lethality, SE and epileptogenesis. Methods: Mice implanted with telemetry transmitters for electroencephalography (EEG) seizure identification were exposed to 80 μg/kg GD and treated with an admix of atropine sulfate (4 mg/kg) and HI-6 (50 mg/kg) 1 min after exposure, and with midazolam (3 mg/kg) alone or in combination with ketamine (30 mg/kg) at 15 or 40 min after seizure onset. Mice were continuously recorded to evaluate initial seizure duration and SRS and then euthanized 2 weeks after exposure for neuropathology assessment. Results: Delayed treatment with midazolam resulted in poor survival, was unable to rapidly terminate behavioral or EEG seizure activity, and did not prevent the development of SRS or neuronal loss following GD exposure. Combination therapy of midazolam and ketamine resulted in improved outcome, including an increase in survival, a reduction in the development of spontaneous recurrent seizures, and reduced neuronal loss, compared to midazolam monotherapy. In addition, dual therapy with ketamine, and midazolam reduced soman-induced activation of micgrolia. Conclusions: This study demonstrates that delayed treatment of SE with midazolam is not fully protective against the GD-induced epileptogenesis and neuropathology, exemplifying the need for adjunct treatment to midazolam to prevent or reduce effects of GD-induced SE. Ketamine combination with midazolam greatly improves survival and reduces epileptogenesis over midazolam monotherapy. Funding: Research was supported by the CounterACT Program, NIH OD, and the NINDS (Grant 1R21NS103820‐01 to LA Lumley‐Lange) and by DTRA-JSTO.Disclaimer. The views expressed are solely those of the authors and do not necessarily represent the official views of the CCRP, NIAID, NIH, HHS, USAMRICD or DoD. The experimental protocol was approved by the Animal Care and Use Committee at the United States Army Medical Research Institute of Chemical Defense, and all procedures were conducted in accordance with the principles stated in the Guide for the Care and Use of Laboratory Animals and the Animal Welfare Act of 1966 (P.L. 89-544), as amended. Erica Kundrick. Erik Matson and Katie Walker were supported in part by an appointment to the Research Participation Program for the U.S. Army Medical Research and Materiel Command administered by the Oak Ridge Institute for Science and Education through an agreement between the U.S. Department of Energy and U.S. Army Medical Research and Materiel Command.