Peripheral and central effects of NADPH oxidase inhibitor, mitoapocynin, in a rat model of diisopropylfluorophosphate (DFP) toxicity

Organophosphates (OP) are highly toxic chemical nerve agents that have been used in chemical warfare. Currently, there are no effective medical countermeasures (MCMs) that mitigate the chronic effects of OP exposure. Oxidative stress is a key mechanism underlying OP-induced cell death and inflammation in the peripheral and central nervous systems and is not mitigated by the available MCMs. NADPH oxidase (NOX) is one of the leading producers of reactive oxygen species (ROS) following status epilepticus (SE). In this study, we tested the efficacy of the mitochondrial-targeted NOX inhibitor, mitoapocynin (MPO) (10 mg/kg, oral), in a rat diisopropylfluorophosphate (DFP) model of OP toxicity. In DFP-exposed animals, MPO decreased oxidative stress markers nitrite, ROS, and GSSG in the serum. Additionally, MPO significantly reduced proinflammatory cytokines IL-1β, IL-6, and TNF-α post-DFP exposure. There was a significant increase in GP91phox, a NOX2 subunit, in the brains of DFP-exposed animals 1-week post-challenge. However, MPO treatment did not affect NOX2 expression in the brain. Neurodegeneration (NeuN and FJB) and gliosis [microglia (IBA1 and CD68), and astroglia (GFAP and C3)] quantification revealed a significant increase in neurodegeneration and gliosis after DFP-exposure. A marginal reduction in microglial cells and C3 colocalization with GFAP in DFP + MPO was observed. The MPO dosing regimen used in this study at 10 mg/kg did not affect microglial CD68 expression, astroglial count, or neurodegeneration. MPO reduced DFP-induced oxidative stress and inflammation markers in the serum but only marginally mitigated the effects in the brain. Dose optimization studies are required to determine the effective dose of MPO to mitigate DFP-induced changes in the brain.

Gut dysbiosis following organophosphate, diisopropylfluorophosphate (DFP), intoxication and saracatinib oral administration

Organophosphate nerve agents (OPNAs) act as irreversible inhibitors of acetylcholinesterase and can lead to cholinergic crisis including salivation, lacrimation, urination, defecation, gastrointestinal distress, respiratory distress, and seizures. Although the OPNAs have been studied in the past few decades, little is known about the impact on the gut microbiome which has become of increasing interest across fields. In this study, we challenged animals with the OPNA, diisopropylfluorophosphate (DFP, 4mg/kg, s.c.) followed immediately by 2mg/kg atropine sulfate (i.m.) and 25mg/kg 2-pralidoxime (i.m.) and 30 minutes later by 3mg/kg midazolam (i.m.). One hour after midazolam, animals were treated with a dosing regimen of saracatinib (SAR, 20mg/kg, oral), a src family kinase inhibitor, to mitigate DFP-induced neurotoxicity. We collected fecal samples 48 hours, 7 days, and 5 weeks post DFP intoxication. 16S rRNA genes (V4) were amplified to identify the bacterial composition. At 48 hours, a significant increase in the abundance of Proteobacteria and decrease in the abundance of Firmicutes were observed in DFP treated animals. At 7 days there was a significant reduction in Firmicutes and Actinobacteria, but a significant increase in Bacteroidetes in the DFP groups compared to controls. The taxonomic changes at 5 weeks were negligible. There was no impact of SAR administration on microbial composition. There was a significant DFP-induced reduction in alpha diversity at 48 hours but not at 7 days and 5 weeks. There appeared to be an impact of DFP on beta diversity at 48 hours and 7 days but not at 5 weeks. In conclusion, acute doses of DFP lead to short-term gut dysbiosis and SAR had no effect. Understanding the role of gut dysbiosis in long-term toxicity may reveal therapeutic targets.

Microglia Remodelling and Neuroinflammation Parallel Neuronal Hyperactivation Following Acute Organophosphate Poisoning

Organophosphate (OP) compounds include highly toxic chemicals widely used both as pesticides and as warfare nerve agents. Existing countermeasures are lifesaving, but do not alleviate all long-term neurological sequelae, making OP poisoning a public health concern worldwide and the search for fully efficient antidotes an urgent need. OPs cause irreversible acetylcholinesterase (AChE) inhibition, inducing the so-called cholinergic syndrome characterized by peripheral manifestations and seizures associated with permanent psychomotor deficits. Besides immediate neurotoxicity, recent data have also identified neuroinflammation and microglia activation as two processes that likely play an important, albeit poorly understood, role in the physiopathology of OP intoxication and its long-term consequences. To gain insight into the response of microglia to OP poisoning, we used a previously described model of diisopropylfluorophosphate (DFP) intoxication of zebrafish larvae. This model reproduces almost all the defects seen in poisoned humans and preclinical models, including AChE inhibition, neuronal epileptiform hyperexcitation, and increased neuronal death. Here, we investigated in vivo the consequences of acute DFP exposure on microglia morphology and behaviour, and on the expression of a set of pro- and anti-inflammatory cytokines. We also used a genetic method of microglial ablation to evaluate the role in the OP-induced neuropathology. We first showed that DFP intoxication rapidly induced deep microglial phenotypic remodelling resembling that seen in M1-type activated macrophages and characterized by an amoeboid morphology, reduced branching, and increased mobility. DFP intoxication also caused massive expression of genes encoding pro-inflammatory cytokines Il1β, Tnfα, Il8, and to a lesser extent, immuno-modulatory cytokine Il4, suggesting complex microglial reprogramming that included neuroinflammatory activities. Finally, microglia-depleted larvae were instrumental in showing that microglia were major actors in DFP-induced neuroinflammation and, more importantly, that OP-induced neuronal hyperactivation was markedly reduced in larvae fully devoid of microglia. DFP poisoning rapidly triggered massive microglia-mediated neuroinflammation, probably as a result of DFP-induced neuronal hyperexcitation, which in turn further exacerbated neuronal activation. Microglia are thus a relevant therapeutic target, and identifying substances reducing microglial activation could add efficacy to existing OP antidote cocktails.