Abstracts

Rationale: Seizures lead to release of large amounts of polyunsaturated fatty acids including arachidonic acid that is metabolized to potent lipid mediators including prostanoids, leukotrienes and epoxyeicosatrienoic acids (EETs). Prostanoids and leukotrienes are mostly pro-inflammatory molecules that sensitize neurons while EETs are anti-inflammatory and are believed to reduce excitability. EET availability in brain can be increased by inhibiting soluble epoxide hydrolase (sEH), the major enzyme that metabolizes EETs to inactive molecules. Intracellular calcium increases during status epilepticus (SE) and persistent high intracellular calcium (“calcium plateaus”) may contribute to the long-term negative consequences of SE. The ryanodine receptor antagonist dantrolene has been shown to prevent calcium plateaus following SE. Here we assessed the effects of the sEH inhibitor 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea, N-[1-(1-oxopropyl)-4-piperidinyl]-N'-[4-(trifluoromethoxy)phenyl]-urea (TPPU) and dantrolene on SE induced by tetramethylenedisulfotetramine (TETS), a highly lethal neurotoxic rodenticide that acts as a noncompetitive GABA_A receptor antagonist and represents a credible chemical threat agent. Methods: Severe TETS intoxication in humans is often associated with refractory convulsive SE. To create a model mimicking these seizures, mice were pretreated with a single dose of riluzole (10 mg/kg, IP) and 10 min later received a lethal dose of TETS (0.2 mg/kg, IP). Riluzole does not inhibit TETS-induced SE but does protect against the rapidly lethal effects of TETS in mice, providing a model of persistent seizure activity. In these experiments, all animals also received midazolam at a human equivalent dose of 1.8 mg/kg (IM), to simulate standard-of-care treatment of nerve agent seizures with a benzodiazepine. Behavioral seizure activity was assessed by visual observation and the latency to cessation of SE after treatment administration was recorded. Animals were monitored for 24 h after seizure termination and the incidence of mortality was recorded. Latency to cessation of SE was defined as the interval between the first behavioral myoclonic twitch and termination of seizure activity. TPPU (3 mg/ml) and dantrolene (20 mg/ml) were prepared, respectively, in a solution containing 24% Captisol in 0.9% saline and in a mixture containing propylene glycol (PG) and ethanol (EtOH) at ratio 7:3 respectively. Midazolam was administered either alone or in combination with TPPU (6 mg/kg, IP) or dantrolene (20 mg/kg, IP) 40 min after the first myoclonic twitch. Dantrolene was also injected 6 h following onset of SE. Results: Co-administration of TPPU with midazolam increased the time to cessation of SE from 6.2 ± 1.7 min (midazolam alone) to 10.6 ± 2.7 min. Moreover, TPPU decreased survival at 24 h from 93% (midazolam alone) to 87%. By contrast, dantrolene did not prolong the time to cessation of SE (7.1 ± 3.0 min) and all animals co-administered dantrolene survived. Conclusions: We conclude that sEH inhibition with TPPU is not a viable protective strategy in TETS induced, whereas blockade of ryanodine receptors with dantrolene may be a beneficial add-on to standard-of-care therapy. It remains to be determined if dantrolene confers neuroprotection on histopathological examination. Funding: NINDS grant #1U54NS079202, DZ, MAR