Antidotal treatment of botulism in rats by continuous infusion with 3,4-diaminopyridine.

Botulinum neurotoxins (BoNTs) are highly potent, select agent toxins that inhibit neurotransmitter release at motor nerve terminals, causing muscle paralysis and death by asphyxiation. Other than post-exposure prophylaxis with antitoxin, the only treatment option for symptomatic botulism is intubation and supportive care until recovery, which can require weeks or longer. In previous studies, we reported the FDA-approved drug 3,4-diaminopyridine (3,4-DAP) reverses early botulism symptoms and prolongs survival in lethally intoxicated mice. However, the symptomatic benefits of 3,4-DAP are limited by its rapid clearance. Here we investigated whether 3,4-DAP could sustain symptomatic benefits throughout the full course of respiratory paralysis in lethally intoxicated rats. First, we confirmed serial injections of 3,4-DAP stabilized toxic signs and prolonged survival in rats challenged with 2.5 LD50 BoNT/A. Rebound of toxic signs and death occurred within hours after the final 3,4-DAP treatment, consistent with the short half-life of 3,4-DAP in rats. Based on these data, we next investigated whether the therapeutic benefits of 3,4-DAP could be sustained throughout the course of botulism by continuous infusion. To ensure administration of 3,4-DAP at clinically relevant doses, three infusion dose rates (0.5, 1.0 and 1.5 mg/kg∙h) were identified that produced steady-state serum levels of 3,4-DAP consistent with clinical dosing. We then compared dose-dependent effects of 3,4-DAP on toxic signs and survival in rats intoxicated with 2.5 LD50 BoNT/A. In contrast to saline vehicle, which resulted in 100% mortality, infusion of 3,4-DAP at ≥ 1.0 mg/kg∙h from 1 to 14 d after intoxication produced 94.4% survival and full resolution of toxic signs, without rebound of toxic signs after infusion was stopped. In contrast, withdrawal of 3,4-DAP infusion at 5 d resulted in re-emergence of toxic sign and death within 12 h, confirming antidotal outcomes require sustained 3,4-DAP treatment for longer than 5 d after intoxication. We exploited this novel survival model of lethal botulism to explore neurophysiological parameters of diaphragm paralysis and recovery. While neurotransmission was nearly eliminated at 5 d, neurotransmission was significantly improved at 21 d in 3,4-DAP-infused survivors, although still depressed compared to naïve rats. 3,4-DAP is the first small molecule to reverse systemic paralysis and promote survival in animal models of botulism, thereby meeting a critical treatment need that is not addressed by post-exposure prophylaxis with conventional antitoxin. These data contribute to a growing body of evidence supporting the use of 3,4-DAP to treat clinical botulism.

Characterization and treatment of spontaneous recurrent seizures following nerve agent-induced status epilepticus in mice.

PURPOSE: To develop and characterize a mouse model of spontaneous recurrent seizures following nerve agent-induced status epilepticus (SE) and test the efficacy of existing antiepileptic drugs. METHODS: SE was induced in telemeterized male C57Bl6/J mice by soman exposure, and electroencephalographic activity was recorded for 4-6 weeks. Mice were treated with antiepileptic drugs (levetiracetam, valproic acid, phenobarbital) or corresponding vehicles for 14 d after exposure, followed by 14 d of drug washout. Survival, body weight, seizure characteristics, and histopathology were used to characterize the acute and chronic effects of nerve agent exposure and to evaluate the efficacy of treatments in mitigating or preventing neurological effects. RESULTS: Spontaneous recurrent seizures manifested in all survivors, but the number and frequency of seizures varied considerably among mice. In untreated mice, seizures became longer over time. Moderate to severe histopathology was observed in the amygdala, piriform cortex, and CA1. Levetiracetam provided modest improvements in neurological parameters such as reduced spike rate and improved histopathology scores, whereas valproic acid and phenobarbital were largely ineffective. CONCLUSIONS: This model of post-SE spontaneous recurrent seizures differs from other experimental models in the brief latency to seizure development, the occurrence of seizures in 100 % of exposed animals, and the lack of damage to CA4/dentate gyrus. It may serve as a useful tool for rapidly and efficiently screening novel therapies that would be effective against severe epilepsy cases.