Editor’s Highlight: Spatiotemporal Progression and Remission of Lesions in the Rat Brain Following Acute Intoxication With Diisopropylfluorophosphate

Abstract

Similar to organophosphate (OP) nerve agents, diisopropylfluorophosphate (DFP) rapidly and irreversibly inhibits acetylcholinesterase, leading to convulsions that can progress to status epilepticus (SE). However, in contrast to the OP nerve agents, the long-term consequences of DFP-induced SE are not well known. Thus, we characterized the spatiotemporal profile of neuropathology during the first 2 months following acute DFP intoxication. Adult, male Sprague Dawley rats administered pyridostigmine bromide (0.1 mg/kg, im) 30 min prior to successive administration of DFP (4 mg/kg, sc), atropine sulfate (2 mg/kg, im), and 2-pralidoxime (25 mg/kg, im), exhibited moderate-to-severe seizure behavior, yet survived until euthanized at 0.5 to 60 days post exposure. Analyses of brains and hearts stained with hematoxylin-eosin, or of brains immunostained for neuronal nuclei (NeuN), glial fibrillary acidic protein (GFAP), or ionized binding adapter molecule 1 (IBA1), revealed progressive neuronal cell death, neuroinflammation, and tissue remodeling across limbic brain regions and the cerebral cortex, with no detectable pathology in the cerebellum or the heart. The lesion type and progression varied according to brain region and time after exposure. Across multiple brain regions, neuronal necrosis peaked after the first week, and neuroinflammation persisted at least 2 months after intoxication. Notably, mineralization was observed at later times in the thalamus, and to a more limited extent, in the hippocampus. Lesion severity was influenced by the initial seizure severity, and spontaneous recurrent seizures were associated with more severe brain damage. These findings parallel descriptions of neuropathology in preclinical models of acute intoxication with OP nerve agents, and other seizurogenic chemicals, suggesting conserved mechanisms of pathology downstream of chemical-induced SE.

Midazolam-Resistant Seizures and Brain Injury after Acute Intoxication of Diisopropylfluorophosphate, an Organophosphate Pesticide and Surrogate for Nerve Agents

“…Effect of Midazolam on DFP-Induced Acute GFAP(1) Astrogliosis and Neuroinflammation. Exposure to OP agents such as sarin or DFP produces massive activation of the neuroinflammatory response (Zimmer et al, 1997;Li et al, 2015;Sisó et al, 2017;Liang et al, 2018). It is associated with astrocytosis and microglial activation in hippocampus, amygdala, and many other brain regions.…”

“…The DFP dose was selected based on the LD 50 in rats and preliminary experiments conducted in accordance with previous publications (Deshpande et al, 2010;Kadriu et al, 2011;Li et al, 2011;Sisó et al, 2017). Moreover, this dosage induced consistent seizure activity and SE in adult rats, a key criterion of an animal model for testing anticonvulsants for OP intoxication.…”

“…OP pesticidesdiisopropylfluorophosphate (DFP), parathion, and paraoxonare considered credible threat agents (Bouzarth and Himwich, 1952;Baille-Le Crom et al, 1995;Kadriu et al, 2009;Wright et al, 2010;Liu et al, 2012;Ferchmin et al, 2014;Li et al, 2015;Flannery et al, 2016). DFP is a potential terrorist threat agent (see Sisó et al (2017)). In addition, thousands of OP pesticide poisonings occur annually due to suicides or accidents worldwide (Savage et al, 1988;Gunnell and Eddleston, 2003;Jokanovi c and Kosanovi c, 2010;Krause et al, 2013).…”

“…In addition, thousands of OP pesticide poisonings occur annually due to suicides or accidents worldwide (Savage et al, 1988;Gunnell and Eddleston, 2003;Jokanovi c and Kosanovi c, 2010;Krause et al, 2013). DFP is commonly used as a surrogate for nerve agents to test the efficacy of medical countermeasures in the National Institutes of Health (NIH) CounterACT program in civilian laboratories (Deshpande et al, 2010;Jett and Yeung, 2010;Reddy and Kuruba, 2013;Pessah et al, 2016;Pouliot et al, 2016;Sisó et al, 2017;Liang et al, 2018;Rojas et al, 2018;Scholl et al, 2018).…”

“…Brain damage is thought to occur not only by seizure-related excitotoxicity (Shih et al, 2003;Prager et al, 2013) but also via mechanisms independent of seizures such as activation of glia and cellular inflammation (Yokoyama, 2007;Banks and Lein, 2012;Pereira et al, 2014). The effects of OP intoxication are long lasting, and survivors suffer chronic brain damage including the risk of neurologic and cognitive deficits (Shih et al, 2003;Yokoyama, 2007;Liu et al, 2012;Prager et al, 2013;Li et al, 2015;Rojas et al, 2015;Flannery et al, 2016;Sisó et al, 2017).…”