Neuroprotection Against Diisopropylfluorophosphate in Acute Hippocampal Slices

Abstract

Diisopropylfluorophosphate (DFP) is an irreversible inhibitor of acetylcholine esterase (AChE) and a surrogate of the organophosphorus (OP) nerve agent sarin. The neurotoxicity of DFP was assessed as a reduction of population spike (PS) area elicited by synaptic stimulation in acute hippocampal slices. Two classical antidotes, atropine, and pralidoxime, and two novel antidotes, 4R-cembranotriene-diol (4R) and a caspase 9 inhibitor, were tested. Atropine, pralidoxime, and 4R significantly protected when applied 30 min after DFP. The caspase inhibitor was neuroprotective when applied 5–10 min before or after DFP, suggesting that early synaptic apoptosis is responsible for the loss of PSs. It is likely that apoptosis starts at the synapses and, if antidotes are not applied, descends to the cell bodies, causing death. The acute slice is a reliable tool for mechanistic studies, and the assessment of neurotoxicity and neuroprotection with PS areas is, in general, pharmacologically congruent with in vivo results and predicts the effect of drugs in vivo. 4R was first found to be neuroprotective in slices and later we demonstrated that 4R is neuroprotective in vivo. The mechanism of neurotoxicity of OPs is not well understood, and there is a need for novel antidotes that could be discovered using acute slices.

Dorsoventral-Specific Effects of Nerve Agent Surrogate Diisopropylfluorophosphate on Synaptic Transmission in the Mouse Hippocampus

“…DFP has previously been employed to investigate the acute effects of an OP on the PS1, a response variable that can be directly correlated to the number of functional pyramidal cells in the stratum pyramidale of CA1 (Williamson and Sarvey, 1985;Jones et al, 1990;Ferchmin et al, 2015). Our results are consistent with these prior reports indicating acute DFP exposure inhibits CA1 glutamatergic transmission and that a substantial component of this inhibition is mediated via cholinergic receptors.…”

“…More specifically, following irreversible inhibition of AChE, enhanced synaptic ACh leads to hyperactivation of mAChRs, a well-established mechanism of OP-induced neurotoxicity (Abou-Donia et al, 2016). Previous studies have shown that mAChR blockade via ATR pretreatment partially prevents DFP-induced PS1 inhibition (Ferchmin et al, 2015). The present study showed that ATR pretreatment not only prevented DFP-mediated inhibition of the dH PS1 amplitude, but the amplitude was in fact significantly enhanced by DFP application.…”

“…DFP is structurally homologous, but significantly less volatile, than nerve agents like sarin, making DFP useful for investigating the mechanisms of sarin and other highly toxic OPs. Accordingly, DFP is one of the most widely studied OP alkylphosphates in the laboratory (Prendergast et al, 1997;Prendergast et al, 1998;Pope et al, 2005;Grigoryan et al, 2008;Nallapaneni et al, 2008;Wright et al, 2010;Terry Jr et al, 2011;Terry Jr et al, 2012;Ferchmin et al, 2015;. Moreover, DFP is currently employed as an initiator of status epilepticus in seizure models (Deshpande et al, 2010;Todorovic et al, 2012;Pouliot et al, 2016) and a nerve agent surrogate in models of Gulf War Illness (O'Callaghan et al, 2015;Phillips et al, 2019).…”

A Review on Bioactivities of Tobacco Cembranoid Diterpenes

“…Tobacco cembranoid diterpenes have excellent neuroprotective activity and could be used to develop drugs for the treatment of nerve damage caused by organophosphorus pesticides [36,37,38,39], Alzheimer’s disease and Parkinson’s disease [43,44,45,46]. Recent studies have shown that β-CBT-diol penetrates the blood–brain barrier to reach the brain to play a neuroprotective role, and pharmacokinetic studies of tobacco cembranoid diterpenes would accelerate the development of neuroprotective drugs [47].…”

4R-Cembranoid Treatment Alters Gene Expression of RAW264.7 Macrophages in Basal and Inflammatory Conditions

“…Notably, post-inflammatory 4R-treatment upregulated genes involved in inflammatory responses in peripheral macrophages after LPS. However, this did not translate into the propagation of cell damage in previously published in vivo experiments [9][10][11]14,15]. The post-inflammatory response to 4R could mean that 4R modulates inflammation in a manner that provides additional immediate support, but not prolonged enough to produce damage.…”