Abstracts

Rationale: Organophosphate (OP) compounds are chemical threat agents and include pesticides and nerve gas agents. Lethal OP exposure could lead to rapid onset of status epilepticus (SE) that is known to injure the heart and the brain. Using the prototype OP agent paraoxon (POX), we recently showed that treatment with atenolol (AT) and levetiracetam (LV) treatment administered after the onset of SE significantly reduced POX-SE mortality. AT is a beta-adrenergic blocker and acts to reduce cardiac stress following SE-induced catecholamine surge while LV is a neuronal calcium-induced calcium release inhibitor and synaptic SV2a inhibitor that exerts a neuroprotective action. Here, we investigated whether combination therapy of AT+LV would protect the heart and the brain from OP-SE vulnerabilities.

Methods: Male Sprague-Dawley rats were injected with POX (2 mg/kg, s.c). One minute later, atropine sulfate (0.5 mg/kg, i.m.) and 2-PAM (25 mg/kg, i.m) were injected. At 1-h post SE onset, midazolam (1.78 mg/kg, i.m.) was used to terminate SE. Rats were than treated with AT (5 mg/kg, i.m.) and LV (50 mg/kg, i.m.) b.i.d. for 7-days. Separate groups of rats were used for each experimental endpoint. In the first group, cardiac irritability was measured by the QTc interval from Electrocardiogram (ECG) analysis out to 8-days post SE-onset. The second group of rats were sacrificed thirty-days post SE, and hearts were processed for the assessment of cardiac pathology. A cardiac damage index (CDI) was calculated that included multiple histopathological features like contraction bands, fibrosis. The third group of rats was assessed for mood and memory function at 8-weeks post SE.

Results: POX-SE caused a significant increase in the QTc interval which was normalized to baseline levels with AT+LV treatment. Analyses of the CDI results showed that AT+LV lowered the CDI from 2.65 ± 0.19 in POX SE rats to 0.76 ± 0.18 in the treatment group (n= 6 rats/ condition, p< 0.001, Tukey-test). On the Forced Swim Test, saline-treated POX rats were immobile for 49.1 ± 3.5% of the duration of the swim session that was significantly higher than the FST immobility of 38.1 ± 2.8% exhibited by AT+LV- treated POX rats (p= 0.02, t-test, n= 10 rats/group). In the open-arm of the Elevated Plus Maze, AT+LV- treated POX rats made significantly higher entries along with significantly lower closed-arm entries compared to saline-treated POX rats (p= 0.01, t-test, n= 10 rats/group). On the Barnes Maze (BM), during the acquisition-phase, latency to escape and the number of errors were significantly lower in AT+LV -treated POX rats compared to saline treatment and, during the probe trial, AT+LV- treated POX rats spent significantly more time in the target quadrant and made significantly more visits to the escape zone compared to saline-treated POX rats.