Persistent neuropathology and behavioral deficits in a mouse model of status epilepticus induced by acute intoxication with diisopropylfluorophosphate

Abstract

Organophosphate (OP) nerve agents and pesticides are a class of neurotoxic compounds that can cause status epilepticus (SE), and death following acute high-dose exposures. While the standard of care for acute OP intoxication (atropine, oxime, and high-dose benzodiazepine) can prevent mortality, survivors of OP poisoning often experience long-term brain damage and cognitive deficits. Preclinical studies of acute OP intoxication have primarily used rat models to identify candidate medical countermeasures. However, the mouse offers the advantage of readily available knockout strains for mechanistic studies of acute and chronic consequences of OP-induced SE. Therefore, the main objective of this study was to determine whether a mouse model of acute diisopropylfluorophosphate (DFP) intoxication would produce acute and chronic neurotoxicity similar to that observed in rat models and humans following acute OP intoxication. Adult male C57BL/6J mice injected with DFP (9.5 mg/kg, s.c.) followed 1 min later with atropine sulfate (0.1 mg/kg, i.m.) and 2-pralidoxime (25 mg/kg, i.m.) developed behavioral and electrographic signs of SE within minutes that continued for at least 4 h. Acetylcholinesterase inhibition persisted for at least 3 d in the blood and 14 d in the brain of DFP mice relative to vehicle (VEH) controls. Immunohistochemical analyses revealed significant neurodegeneration and neuroinflammation in multiple brain regions at 1, 7, and 28 d post-exposure in the brains of DFP mice relative to VEH controls. Deficits in locomotor and home-cage behavior were observed in DFP mice at 28 d post-exposure. These findings demonstrate that this mouse model replicates many of the outcomes observed in rats and humans acutely intoxicated with OPs, suggesting the feasibility of using this model for mechanistic studies and therapeutic screening.

Long-Term Anxiety-like Behavior and Microbiota Changes Induced in Mice by Sublethal Doses of Acute Sarin Surrogate Exposure

“…Anxiety disorder is one of the most reported disorders in animal models in response to OP exposure [10,[33][34][35][36]. Generally, such behavioral assessments are conducted in animals exposed to high doses of OP that show persistent mood disorder defects [33,34]. Similar results have also been observed for the development of anxiety-like behavior in animals exposed to sublethal dose of OP [10,37] and are consistent with reports in humans [2,38,39].…”

“…Anxiety disorder is one of the most reported disorders in animal models in response to OP exposure [10,[33][34][35][36]. Generally, such behavioral assessments are conducted in animals exposed to high doses of OP that show persistent mood disorder defects [33,34].…”

The α4 nicotinic acetylcholine receptor is necessary for the initiation of organophosphate-induced neuronal hyperexcitability

“…To confirm the physiological relevance of findings in acute hippocampal slices, we evaluated the effects of pharmacological antagonism or genetic deletion of nAChR on behavioral seizures and electroencephalographic (EEG) activity in a mouse model of acute DFP intoxication (Calsbeek et al, 2021). In our initial behavioral assessments, mice pretreated with either the nonspecific nAChR antagonist MEC or the α4-selective antagonist DHβE, and α4 KO mice displayed attenuated seizure activity compared to Veh/WT (Supplemental Fig.…”

“…For example, most in vitro model systems comprised of primary neurons are derived from the developing brain, and developing neurons fail to express and properly target functional nAChRs to synaptic junctions and extra-junctional locations (Srinivasan et al, 2011; Zambrano et al, 2015). Here, we leverage our observation that functional nAChR are expressed in acute hippocampal slice cultures derived from adult mice, and adopted our mouse model of acute intoxication with the OP diisopropylfluorophosphate (DFP) (Calsbeek et al, 2021) to transgenic mice with specific nAChR subunits genetically deleted to assess the role of nAChR in OP-induced SE.…”

Diisopropylfluorophosphate (DFP) volatizes and cross-contaminates wells in a common 96-well plate format used in zebrafish larvae toxicology studies

“…Self-poisonings with OP pesticides are estimated to occur at a rate of approximately 200,000 per year in developing countries (Eddleston, Buckley, Eyer, & Dawson, 2008;Gunnell, Eddleston, Phillips, & Konradsen, 2007), and OPs weaponized as chemical threat agents have been used in wars and acts of terrorism (Haley, 2018;Vogel, 2013). Non-fatal outcomes of acute OP poisonings can be severe and long-lasting, and include the development of epilepsy and impaired learning and memory in humans (Chen, 2012;Jett et al, 2020) and experimental rat (González et al, 2020;Guignet et al, 2020;Hobson et al, 2019) and mouse (Calsbeek et al, 2021) models. Thus, there is great interest in characterizing and understanding OP neurotoxicity to identify novel, mechanistically relevant therapeutic targets for mitigating adverse effects.…”