Exposure to nerve agents: from status epilepticus to neuroinflammation, brain damage, neurogenesis and epilepsy

Neuroprotective effects of a catalytic antioxidant in a rat nerve agent model

Persistent inhibition of acetylcholinesterase resulting from exposure to nerve agents such as soman, is associated with prolonged seizure activity known as status epilepticus (SE). Without medical countermeasures, exposure to soman and resultant SE leads to high morbidity and mortality. Currently available therapeutics are effective in limiting mortality, however effects on morbidity are highly time-dependent and rely on the ability to suppress SE. We have previously demonstrated significant protection from secondary neuronal injury in surrogate nerve agent models by targeting oxidative stress. However, whether oxidative stress represents a relevant therapeutic target in genuine nerve agent toxicity is unknown. Here, we demonstrate that soman exposure results in robust region- and time-dependent oxidative stress. Targeting this oxidative stress in a post-exposure paradigm using a small molecular weight, broad spectrum catalytic antioxidant, was sufficient to attenuate brain and plasma oxidative stress, neuroinflammation and neurodegeneration. Thus, targeting of oxidative stress in a post-exposure paradigm can mitigate secondary neuronal injury following soman exposure.

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Soman exposure results in time- and region- dependent oxidative stress in brain.

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A catalytic antioxidant inhibited oxidative stress, neuroinflammation and degeneration.

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Post-exposure treatment with the antioxidant attenuates secondary neuronal injury.

Benzodiazepine-refractory status epilepticus, neuroinflammation, and interneuron neurodegeneration after acute organophosphate intoxication

Nerve agents and some pesticides such as diisopropylfluorophosphate (DFP) cause neurotoxic manifestations that include seizures and status epilepticus (SE), which are potentially lethal and carry long-term neurological morbidity. Current antidotes for organophosphate (OP) intoxication include atropine, 2-PAM and diazepam (a benzodiazepine for treating seizures and SE). There is some evidence for partial or complete loss of diazepam anticonvulsant efficacy when given 30 min or later after exposure to an OP; this condition is known as refractory SE. Effective therapies for OP-induced SE are lacking and it is unclear why current therapies do not work. In this study, we investigated the time-dependent efficacy of diazepam in the nerve agent surrogate DFP model of OP intoxication on seizure suppression and neuroprotection in rats, following an early and late therapy. Diazepam (5 mg/kg, IM) controlled seizures when given 10 min after DFP exposure ("early"), but it was completely ineffective at 60 or 120 min ("late") after DFP. DFP-induced neuronal injury, neuroinflammation, and neurodegeneration of principal cells and GABAergic interneurons were significantly reduced by early but not late therapy. These findings demonstrate that diazepam failed to control seizures, SE and neuronal injury when given 60 min or later after DFP exposure, confirming the benzodiazepine-refractory SE and brain damage after OP intoxication. In addition, this study indicates that degeneration of inhibitory interneurons and inflammatory glial activation are potential mechanisms underlying these morbid outcomes of OP intoxication. Therefore, novel anticonvulsant and neuroprotectant antidotes, superior to benzodiazepines, are desperately needed for controlling nerve agent-induced SE and brain injury.

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

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.

Beneficial Outcome of Urethane Treatment Following Status Epilepticus in a Rat Organophosphorus Toxicity Model

The efficacy of benzodiazepines to terminate electrographic status epilepticus (SE) declines the longer a patient is in SE. Therefore, alternative methods for ensuring complete block of SE and refractory SE are necessary. We compared the ability of diazepam and a subanesthetic dose of urethane to terminate prolonged SE and mitigate subsequent pathologies. Adult Sprague Dawley rats were injected with diisopropylfluorophosphate (DFP) to induce SE. Rats were administered diazepam (10 mg/kg, ip) or urethane (0.8 g/kg, s.c.) 1 h after DFP-induced SE and compared to rats that experienced uninterrupted SE. Large-amplitude and high-frequency spikes induced by DFP administration were quenched for at least 46 h in rats administered urethane 1 h after SE onset as demonstrated by cortical electroencephalography (EEG). By contrast, diazepam interrupted SE but seizures with high power in the 20- to 70-Hz band returned 6-10 h later. Urethane was more effective than diazepam at reducing hippocampal neurodegeneration, brain inflammation, gliosis and weight loss as measured on day 4 after SE. Furthermore, rats administered urethane displayed a 73% reduction in the incidence of spontaneous recurrent seizures after four to eight weeks and a 90% reduction in frequency of seizures in epileptic rats. By contrast, behavioral changes in the light/dark box, open field and a novel object recognition task were not improved by urethane. These findings indicate that in typical rodent SE models, it is the return of SE overnight, and not the initially intense 1-2 h of SE experience, that is largely responsible for neurodegeneration, accompanying inflammation, and the subsequent development of epilepsy.

Glial source of nitric oxide in epileptogenesis: A target for disease modification in epilepsy

Epileptogenesis is the process of developing an epileptic condition and/or its progression once it is established. The molecules that initiate, promote, and propagate remarkable changes in the brain during epileptogenesis are emerging as targets for prevention/treatment of epilepsy. Epileptogenesis is a continuous process that follows immediately after status epilepticus (SE) in animal models of acquired temporal lobe epilepsy (TLE). Both SE and epileptogenesis are potential therapeutic targets for the discovery of anticonvulsants and antiepileptogenic or disease-modifying agents. For translational studies, SE targets are appropriate for screening anticonvulsive drugs prior to their advancement as therapeutic agents, while targets of epileptogenesis are relevant for identification and development of therapeutic agents that can either prevent or modify the disease or its onset. The acute seizure models do not reveal antiepileptogenic properties of anticonvulsive drugs. This review highlights the important components of epileptogenesis and the long-term impact of intervening one of these components, nitric oxide (NO), in rat and mouse kainate models of TLE. NO is a putative pleotropic gaseous neurotransmitter and an important contributor of nitro-oxidative stress that coexists with neuroinflammation and epileptogenesis. The long-term impact of inhibiting the glial source of NO during early epileptogenesis in the rat model of TLE is reviewed. The importance of sex as a biological variable in disease modification strategies in epilepsy is also briefly discussed.

Flupirtine and diazepam combination terminates established status epilepticus: results in three rodent models

Objective

Status epilepticus (SE) is a neurological emergency requiring rapid termination of seizures. New treatment choices are needed for benzodiazepine-refractory SE or established SE (ESE). Previous studies have demonstrated that the potassium-channel opener flupirtine terminates seizures in neonatal animals. However, its effectiveness in adult ESE has not been tested. We tested whether flupirtine alone or in combination with the benzodiazepine diazepam would terminate ESE in three animal models.

Methods

SE was induced by administration of lithium followed by pilocarpine, by electrical stimulation of the hippocampus or by diisopropylfluorophosphate (DFP) administration. Seizures were assessed by EEG recorded from the hippocampus and cortex.

Results

Flupirtine alone did not terminate ESE within 60 min of administration in any of the three models of ESE. A combination of flupirtine and diazepam terminated ESE within 60 min in all the three models. The drug combination shortened the duration of ESE in all three models. Drug responsiveness was distinct between each model.

Conclusion

A combination of the potassium channel opener flupirtine and diazepam is a potential therapy for ESE.

From the Cover: MagneticResonance Imaging Reveals Progressive Brain Injury in Rats Acutely Intoxicated With Diisopropylfluorophosphate

Acute intoxication with organophosphates (OPs) can trigger seizures that progress to status epilepticus, and survivors often exhibit chronic neuropathology, cognitive impairment, affective disorders, and/or electroencephalographic abnormalities. Understanding how acute injury transitions to persistent neurological sequelae is critical to developing medical countermeasures for mitigating damage following OP-induced seizures. Here, we used in vivo magnetic resonance imaging (MRI) to monitor the spatiotemporal patterns of neuropathology for 1 month after acute intoxication with diisopropylfluorophosphate (DFP). 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. T2-weighted and diffusion-weighted MR imaging prior to DFP exposure and at 3, 7, 14, 21, or 28 days postexposure revealed prominent lesions, tissue atrophy, and ventricular enlargement in discrete brain regions. Lesions varied in intensity and/or extent over time, with the overall magnitude of injury strongly influenced by seizure severity. Importantly, lesions detected by MRI correlated spatially and temporally with histological evidence of brain pathology. Analysis of histogram parameters extracted from frequency distributions of regional apparent diffusion coefficient (ADC) values identified the standard deviation and 90th percentile of the ADC as robust metrics for quantifying persistent and progressive neuropathological changes. The interanimal and interregional variations observed in lesion severity and progression, coupled with potential reinjury following spontaneous recurrent seizures, underscore the advantages of using in vivo imaging to longitudinally monitor neuropathology and, ultimately, therapeutic response, following acute OP intoxication.

Novel therapeutic approaches for disease-modification of epileptogenesis for curing epilepsy

This article describes the recent advances in epileptogenesis and novel therapeutic approaches for the prevention of epilepsy, with a special emphasis on the pharmacological basis of disease-modification of epileptogenesis for curing epilepsy. Here we assess animal studies and human clinical trials of epilepsy spanning 1982-2016. Epilepsy arises from a number of neuronal factors that trigger epileptogenesis, which is the process by which a brain shifts from a normal physiologic state to an epileptic condition. The events precipitating these changes can be of diverse origin, including traumatic brain injury, cerebrovascular damage, infections, chemical neurotoxicity, and emergency seizure conditions such as status epilepticus. Expectedly, the molecular and system mechanisms responsible for epileptogenesis are not well defined or understood. To date, there is no approved therapy for the prevention of epilepsy. Epigenetic dysregulation, neuroinflammation, and neurodegeneration appear to trigger epileptogenesis. Targeted drugs are being identified that can truly prevent the development of epilepsy in at-risk people. The promising agents include rapamycin, COX-2 inhibitors, TRK inhibitors, epigenetic modulators, JAK-STAT inhibitors, and neurosteroids. Recent evidence suggests that neurosteroids may play a role in modulating epileptogenesis. A number of promising drugs are under investigation for the prevention or modification of epileptogenesis to halt the development of epilepsy. Some drugs in development appear rational for preventing epilepsy because they target the initial trigger or related signaling pathways as the brain becomes progressively more prone to seizures. Additional research into the target validity and clinical investigation is essential to make new frontiers in curing epilepsy.

Oxidative Stress Contributes to Status Epilepticus Associated Mortality

Status epilepticus is a common manifestation of nerve agent toxicity and represents a serious medical emergency with high rates of mortality and neurologic injury in those that survive. The aim of the current study was to determine if targeting oxidative stress with the catalytic antioxidant, AEOL10150, would reduce pilocarpine-induced mortality and attenuate neuronal death and neuroinflammation. We found that treatment with AEOL10150 in conjunction with scopolamine and diazepam following pilocarpine-induced SE was able to significantly reduce mortality compared to treatment with just scopolamine and diazepam. Mortality was further reduced when AEOL10150 was used in conjunction with atropine and diazepam which is considered the standard of care for nerve agent exposures. Both treatment paradigms offered significant protection against SE-induced oxidative stress. Additionally, treatment with scopolamine, AEOL10150 and diazepam attenuated SE-induced neuronal loss and neuroinflammation. Taken together, the data suggest that pharmacological targeting of oxidative stress can improve survival and attenuate secondary neurological damage following SE induced by the nerve agent surrogate pilocarpine.

The synthetic neuroactive steroid SGE-516 reduces status epilepticus and neuronal cell death in a rat model of soman intoxication

Organophosphorus nerve agents (OPNAs) are irreversible inhibitors of acetylcholinesterase that pose a serious threat to public health because of their use as chemical weapons. Exposure to high doses of OPNAs can dramatically potentiate cholinergic synaptic activity and cause status epilepticus (SE). Current standard of care for OPNA exposure involves treatment with cholinergic antagonists, oxime cholinesterase reactivators, and benzodiazepines. However, data from pre-clinical models suggest that OPNA-induced SE rapidly becomes refractory to benzodiazepines. Neuroactive steroids (NAS), such as allopregnanolone, retain anticonvulsant activity in rodent models of benzodiazepine-resistant SE, perhaps because they modulate a broader variety of GABA_A receptor subtypes. SGE-516 is a novel, next generation NAS and a potent and selective GABA_A receptor positive allosteric modulator (PAM). The present study first established that SGE-516 reduced electrographic seizures in the rat lithium-pilocarpine model of pharmacoresistant SE. Then the anticonvulsant activity of SGE-516 was investigated in the soman-intoxication model of OPNA-induced SE. SGE-516 (5.6, 7.5, and 10mg/kg, IP) significantly reduced electrographic seizure activity compared to control when administered 20min after SE onset. When 10mg/kg SGE-516 was administered 40min after SE onset, seizure activity was still significantly reduced compared to control. In addition, all cohorts of rats treated with SGE-516 exhibited significantly reduced neuronal cell death as measured by FluoroJade B immunohistochemistry. These data suggest synthetic NASs that positively modulate both synaptic and extrasynaptic GABA_A receptors may be candidates for further study in the treatment of OPNA-induced SE.

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

Persistent neuroinflammation and cognitive impairment in a rat model of acute diisopropylfluorophosphate intoxication

Background

Acute intoxication with organophosphorus (OP) cholinesterase inhibitors can trigger convulsions that progress to life-threatening status epilepticus. Survivors face long-term morbidity including mild-to-severe decline in memory. It is posited that neuroinflammation plays a key role in the pathogenesis of OP-induced neuropsychiatric deficits. Rigorous testing of this hypothesis requires preclinical models that recapitulate relevant phenotypic outcomes. Here, we describe a rat model of acute intoxication with the OP diisopropylfluorophosphate (DFP) that exhibits persistent neuroinflammation and cognitive impairment.

Methods

Neuroinflammation, neurodegeneration, and cognitive function were compared in adult male Sprague Dawley rats injected with an acutely toxic dose of DFP vs. vehicle controls at multiple time points up to 36 days post-exposure. Neuroinflammation was quantified using immunohistochemical biomarkers of microglia (ionized calcium-binding adapter molecule 1, IBA1) and activated astrocytes (glial fibrillary acidic protein, GFAP) and positron emission tomography (PET) imaging of [¹¹C]-(R)-PK11195, a ligand for the 18-kDa mitochondrial membrane translocator protein (TSPO). FluoroJade-B staining was used to assess neurodegeneration; Pavlovian conditioning, to assess cognitive function.

Results

Animals exhibited moderate-to-severe seizures within minutes of DFP injection that continued for up to 6 h post-injection. As indicated by IBA1 and GFAP immunoreactivity and by PET imaging of TSPO, acute DFP intoxication triggered neuroinflammation in the hippocampus and cortex during the first 3 days that peaked at 7 days and persisted to 21 days post-exposure in most animals. Neurodegeneration was detected in multiple brain regions from 1 to 14 days post-exposure. All DFP-intoxicated animals exhibited significant deficits in contextual fear conditioning at 9 and 20 days post-exposure compared to vehicle controls. Whole-brain TSPO labeling positively correlated with seizure severity score, but did not correlate with performance in the contextual fear-conditioning task.

Conclusions

We describe a preclinical model in which acute DFP intoxication causes seizures, persistent neuroinflammation, neurodegeneration, and memory impairment. The extent of the neuroinflammatory response is influenced by seizure severity. However, the observation that a subset of animals with moderate seizures and minimal TSPO labeling exhibited cognitive deficits comparable to those of animals with severe seizures and significant TSPO labeling suggests that DFP may impair learning and memory circuitry via mechanisms independent of seizures or neuroinflammation.

Inhibition of the prostaglandin E2 receptor EP2 prevents status epilepticus-induced deficits in the novel object recognition task in rats

Survivors of exposure to an organophosphorus nerve agent may develop a number of complications including long-term cognitive deficits (Miyaki et al., 2005; Nishiwaki et al., 2001). We recently demonstrated that inhibition of the prostaglandin E2 receptor, EP2, attenuates neuroinflammation and neurodegeneration caused by status epilepticus (SE) induced by the soman analog, diisopropylfluorophosphate (DFP), which manifest within hours to days of the initial insult. Here, we tested the hypothesis that DFP exposure leads to a loss of cognitive function in rats that is blocked by early, transient EP2 inhibition. Adult male Sprague-Dawley rats were administered vehicle or the competitive EP2 antagonist, TG6-10-1, (ip) at various times relative to DFP-induced SE. DFP administration resulted in prolonged seizure activity as demonstrated by cortical electroencephalography (EEG). A single intraperitoneal injection of TG6-10-1 or vehicle 1 h prior to DFP did not alter the development of seizures, the latency to SE or the duration of SE. Rats administered six injections of TG6-10-1 starting 90 min after the onset of DFP-induced SE could discriminate between a novel and familiar object 6-12 weeks after SE, unlike vehicle treated rats which showed no preference for the novel object. By contrast, behavioral changes in the light-dark box and open field assays were not affected by TG6-10-1. Delayed mortality after DFP was also unaffected by TG6-10-1. Thus, selective inhibition of the EP2 receptor may prevent SE-induced memory impairment in rats caused by exposure to a high dose of DFP.

Models to identify treatments for the acute and persistent effects of seizure-inducing chemical threat agents

Exposures to seizure-inducing chemical threat agents are a major public health concern. Of particular need is improved treatment to terminate convulsions and to prevent the long-term neurological sequelae in survivors. We are studying the organophosphorus cholinesterase inhibitor diisopropyl fluorophosphate (DFP) and the GABA receptor inhibitor tetramethylenedisulfotetramine (TETS), which arguably encompass the mechanistic spectrum of seizure-inducing chemical threats, with the goal of identifying therapeutic approaches with broad-spectrum efficacy. Research efforts have focused on developing translational models and translational diagnostic approaches, including (1) in vivo models of DFP- and TETS-induced seizures for studying neuropathological mechanisms and identifying treatment approaches; (2) in vivo imaging modalities for noninvasive longitudinal monitoring of neurological damage and response to therapeutic candidates; and (3) higher-throughput in vitro platforms for rapid screening of compounds to identify potential antiseizure and neuroprotective agents, as well as mechanistically relevant novel drug targets. This review summarizes our progress toward realizing these goals and discusses best practices and mechanistic insights derived from our modeling efforts.

Neuroinflammation-Induced Memory Deficits Are Amenable to Treatment with D-Cycloserine

Cognitive deficits, especially memory loss, are common following many types of brain insults which are associated with neuroinflammation, although the underlying mechanisms are not entirely clear. The present study aimed to characterize the long-term cognitive and behavioral impairments in a mouse model of neuroinflammation in the absence of other insults and to evaluate the therapeutic potential of D-cycloserine (DCS). DCS is a co-agonist of the NMDA receptor that ameliorates cognitive deficits in models of TBI and stroke. Using a mouse model of global neuroinflammation induced by intracisternal (i.c.) administration of endotoxin (LPS), we found long-lasting microgliosis, memory deficits, impaired LTP, and reduced levels of the obligatory NR1 subunit of the NMDA receptor. A single administration of DCS, 1 day after i.c. LPS reduced microgliosis, reversed the cognitive deficits and restored LTP and NR1 levels. These results demonstrate that neuroinflammation alone, in the absence of trauma or ischemia, can cause persistent (>6 months) memory deficits linked to deranged NNMDA receptor function and suggest a possible role for NMDA co-agonists in reducing the cognitive sequelae of neuroinflammation.

Role of the calcium plateau in neuronal injury and behavioral morbidities following organophosphate intoxication

Organophosphate (OP) chemicals include nerve agents and pesticides, and there is a growing concern of OP-based chemical attacks against civilians. Current antidotes are essential in limiting immediate mortality associated with OP exposure. However, further research is needed to identify the molecular mechanisms underlying long-term neurological deficits following survival of OP toxicity in order to develop effective therapeutics. We have developed rat survival models of OP-induced status epilepticus (SE) that mimic chronic mortality and morbidity following OP intoxication. We have observed significant elevations in hippocampal calcium levels after OP SE that persisted for weeks following initial survival. Drugs inhibiting intracellular calcium-induced calcium release, such as dantrolene, levetiracetam, and carisbamate, lowered OP SE-mediated protracted calcium elevations. Given the critical role of calcium signaling in modulating behavior and cell death mechanisms, drugs targeted at preventing the development of the calcium plateau could enhance neuroprotection, help reduce morbidity, and improve outcomes following survival of OP SE.

Younger rats are more susceptible to the lethal effects of sarin than adult rats: 24 h LC50 for whole-body (10 and 60 min) exposures

Chemical warfare nerve agents (CWNA) inhibit acetylcholinesterase and are among the most lethal chemicals known to man. Children are predicted to be vulnerable to CWNA exposure because of their smaller body masses, higher ventilation rates and immature central nervous systems. While a handful of studies on the effects of CWNA in younger animals have been published, exposure routes relevant to battlefield or terrorist situations (i.e. inhalation for sarin) were not used. Thus, we estimated the 24 h LC₅₀ for whole-body (10 and 60 min) exposure to sarin using a stagewise, adaptive dose design. Specifically, male and female Sprague-Dawley rats were exposed to a range of sarin concentrations (6.2-44.0 or 1.6-12.5 mg/m³) for either 10 or 60 min, respectively, at six different times during their development (postnatal day [PND] 7, 14, 21, 28, 42 and 70). For male and female rats, the lowest LC₅₀ values were observed for PND 14 and the highest LC₅₀ values for PND 28. Sex differences were observed only for PND 42 for the 10 min exposures and PND 21 and 70 for the 60 min exposures. Thus, younger rats (PND 14) were more susceptible than older rats (PND 70) to the lethal effects of whole-body exposure to sarin, while adolescent (PND 28) rats were the least susceptible and sex differences were minimal. These results underscore the importance of controlling for the age of the animal in research on the toxic effects associated with CWNA exposure.

Pharmacological blockade of the calcium plateau provides neuroprotection following organophosphate paraoxon induced status epilepticus in rats

Organophosphate (OP) compounds which include nerve agents and pesticides are considered chemical threat agents. Currently approved antidotes are crucial in limiting OP mediated acute mortality. However, survivors of lethal OP exposure exhibit delayed neuronal injury and chronic behavioral morbidities. In this study, we investigated neuroprotective capabilities of dantrolene and carisbamate in a rat survival model of paraoxon (POX) induced status epilepticus (SE). Significant elevations in hippocampal calcium levels were observed 48-h post POX SE survival, and treatment with dantrolene (10mg/kg, i.m.) and carisbamate (90mg/kg, i.m.) lowered these protracted calcium elevations. POX SE induced delayed neuronal injury as characterized by Fluoro Jade C labeling was observed in critical brain areas including the dentate gyrus, parietal cortex, amygdala, and thalamus. Dantrolene and carisbamate treatment provided significant neuroprotection against delayed neuronal damage in these brain regions when administered one-hour after POX-SE. These results indicate that dantrolene or carisbamate could be effective adjuvant therapies to the existing countermeasures to reduce neuronal injury and behavioral morbidities post OP SE survival.

Long-term neuropathological and behavioral impairments after exposure to nerve agents

One of the deleterious effects of acute nerve agent exposure is the induction of status epilepticus (SE). If SE is not controlled effectively, it causes extensive brain damage. Here, we review the neuropathology observed after nerve agent-induced SE, as well as the ensuing pathophysiological, neurological, and behavioral alterations, with an emphasis on their time course and longevity. Limbic structures are particularly vulnerable to damage by nerve agent exposure. The basolateral amygdala (BLA), which appears to be a key site for seizure initiation upon exposure, suffers severe neuronal loss; however, GABAergic BLA interneurons display a delayed death, perhaps providing a window of opportunity for rescuing intervention. The end result is a long-term reduction of GABAergic activity in the BLA, with a concomitant increase in spontaneous excitatory activity; such pathophysiological alterations are not observed in the CA1 hippocampal area, despite the extensive neuronal loss. Hyperexcitability in the BLA may be at least in part responsible for the development of recurrent seizures and increased anxiety, while hippocampal damage may underlie the long-term memory impairments. Effective control of SE after nerve agent exposure, such that brain damage is also minimized, is paramount for preventing lasting neurological and behavioral deficits.

Human skin-derived precursor cells are poorly immunogenic and modulate the allogeneic immune response

Human skin-derived precursors (hSKPs) are multipotent somatic stem cells that persist within the dermis throughout adulthood and harbor potential clinical applicability. In this study, we investigated their immunogenicity and immunosuppressive features, both in vitro and in vivo. As such, this study provides a solid basis for developing their future clinical applications. We found that hSKPs express HLA-ABC molecules, but not HLA-DR, rendering them poorly immunogenic. Using a coculture set-up, we could further demonstrate that hSKPs inhibit the proliferation of allogeneic activated T cells and alter their cytokine secretion profile, in a dose-dependent manner. Cotransplantation of hSKP and human peripheral blood leukocytes (PBL) into severe combined immune-deficient mice also showed a significant impairment of the graft-versus-host response 1 week post-transplantation and a drastic increase in survival time of 60%. From a mechanistic point of view, we found that hSKPs require cell contact as well as secretion of soluble inhibitory factors in order to modulate the immune response. The expression/secretion levels of these factors further increases upon inflammation or in the presence of activated T cells. As such, we believe that these features could be beneficial in a later allogeneic clinical setting, because rejection of engrafted allogeneic hSKP might be delayed or even avoided due to their own promotion of a tolerogenic microenvironment.

Pilocarpine-induced convulsive activity is limited by multidrug transporters at the rodent blood-brain barrier

As a result of the growing availability of genetically engineered mouse lines, the pilocarpine post-status epilepticus (SE) model of temporal lobe epilepsy is increasingly used in mice. A discrepancy in pilocarpine sensitivity in FVB/N wild-type versus P-glycoprotein (PGP)-deficient mice precipitated the investigation of the interaction between pilocarpine and two major multidrug transporters at the blood-brain barrier. Doses of pilocarpine necessary for SE induction were determined in male and female wild-type and PGP-deficient mice. Brain and plasma concentrations were measured following low (30-50 mg⋅kg(-1) i.p.) and/or high (200 mg⋅kg(-1) i.p.) doses of pilocarpine in wild-type mice, and mice lacking PGP, breast cancer resistance protein (BCRP), or both transporters, as well as in rats with or without pretreatment with lithium chloride or tariquidar. Concentration equilibrium transport assays (CETA) were performed using cells overexpressing murine PGP or BCRP. Lower pilocarpine doses were necessary for SE induction in PGP-deficient mice. Brain-plasma ratios were higher in mice lacking PGP or PGP and BCRP, which was also observed after pretreatment with tariquidar in mice and in rats. Lithium chloride did not change brain penetration of pilocarpine. CETA confirmed transport of pilocarpine by PGP and BCRP. Pilocarpine is a substrate of PGP and BCRP at the rodent blood-brain barrier, which restricts its convulsive action. Future studies to reveal whether strain differences in pilocarpine sensitivity derive from differences in multidrug transporter expression levels are warranted.

Angiotensin II and its receptor in activated microglia enhanced neuronal loss and cognitive impairment following pilocarpine-induced status epilepticus

Neuroinflammation plays a role in the pathology of epilepsy and in cognitive impairment. Angiotensin II (AII) and the angiotensin receptor type 1 (AT1) have been shown to regulate seizure susceptibility in different models of epilepsy. Inhibition of AT1 attenuates neuroinflammatory responses in different neurological diseases. In the present study, we showed that the protein expression of AII and AT1 was increased in activated microglia following lithium pilocarpine-induced status epilepticus (SE) in rats. Furthermore, the AT1 receptor antagonist, losartan, significantly inhibited SE-induced cognitive impairment and microglia-mediated inflammation. Losartan also prevented SE induced neuronal loss in the hippocampus and exerted neuroprotection. These data suggest that losartan improves SE-induced cognitive impairment by suppressing microglia mediated inflammatory responses and attenuating hippocampal neuronal loss. Overall, our findings provide a possible therapeutic strategy for the treatment of cognitive impairment in epilepsy.

Comparison of intranasal and intravenous diazepam on status epilepticus in stroke patients: a retrospective cohort study

Administering diazepam intravenously or rectally in an adult with status epilepticus can be difficult and time consuming. The aim of this study was to examine whether intranasal diazepam is an effective alternative to intravenous diazepam when treating status epilepticus. We undertook a retrospective cohort study based on the medical records of 19 stroke patients presenting with status epilepticus to our institution. We measured the time between arrival at the hospital, the intravenous or intranasal administration of diazepam, and the seizure termination. Intranasal diazepam was administered about 9 times faster than intravenous diazepam (1 vs 9.5 minutes, P = 0.001), resulting in about 3-fold reduction in the time to termination of seizure activity after arrival at the hospital (3 minutes compared with 9.5 minutes in the intravenous group, P = 0.030). No adverse effects of intranasal diazepam were evident from the medical records. Intranasal diazepam administration is safer, easier, and quicker than intravenous administration.

Rapid throughput analysis demonstrates that chemicals with distinct seizurogenic mechanisms differentially alter Ca2+ dynamics in networks formed by hippocampal neurons in culture

Primary cultured hippocampal neurons (HN) form functional networks displaying synchronous Ca(2+) oscillations (SCOs) whose patterns influence plasticity. Whether chemicals with distinct seizurogenic mechanisms differentially alter SCO patterns was investigated using mouse HN loaded with the Ca(2+) indicator fluo-4-AM. Intracellular Ca(2+) dynamics were recorded from 96 wells simultaneously in real-time using fluorescent imaging plate reader. Although quiescent at 4 days in vitro (DIV), HN acquired distinctive SCO patterns as they matured to form extensive dendritic networks by 16 DIV. Challenge with kainate, a kainate receptor (KAR) agonist, 4-aminopyridine (4-AP), a K(+) channel blocker, or pilocarpine, a muscarinic acetylcholine receptor agonist, caused distinct changes in SCO dynamics. Kainate at <1 µM produced a rapid rise in baseline Ca(2+) (Phase I response) associated with high-frequency and low-amplitude SCOs (Phase II response), whereas SCOs were completely repressed with >1 µM kainate. KAR competitive antagonist CNQX [6-cyano-7-nitroquinoxaline-2,3-dione] (1-10 µM) normalized Ca(2+) dynamics to the prekainate pattern. Pilocarpine lacked Phase I activity but caused a sevenfold prolongation of Phase II SCOs without altering either their frequency or amplitude, an effect normalized by atropine (0.3-1 µM). 4-AP (1-30 µM) elicited a delayed Phase I response associated with persistent high-frequency, low-amplitude SCOs, and these disturbances were mitigated by pretreatment with the KCa activator SKA-31 [naphtho[1,2-d]thiazol-2-ylamine]. Consistent with its antiepileptic and neuroprotective activities, nonselective voltage-gated Na(+) and Ca(2+) channel blocker lamotrigine partially resolved kainate- and pilocarpine-induced Ca(2+) dysregulation. This rapid throughput approach can discriminate among distinct seizurogenic mechanisms that alter Ca(2+) dynamics in neuronal networks and may be useful in screening antiepileptic drug candidates.

Caramiphen edisylate: an optimal antidote against organophosphate poisoning

Potent cholinesterase inhibitors such as sarin, induce an array of harmful effects including hypersecretion, convulsions and ultimately death. Surviving subjects demonstrate damage in specific brain regions that lead to cognitive and neurological dysfunctions. An early accumulation of acetylcholine in the synaptic clefts was suggested as the trigger of a sequence of neurochemical events such as an excessive outpour of glutamate and activation of its receptors. Indeed, alterations in NMDA and AMPA central receptors' densities were detected in brains of poisoned animals. Attempts to improve the current cholinergic-based treatment by adding potent anticonvulsants or antiglutamatergic drugs produced unsatisfactory results. In light of recent events in Syria and the probability of various scenarios of military or terrorist attacks involving organophosphate (OP) nerve agent, research should focus on finding markedly improved countermeasures. Caramiphen, an antimuscarinic drug with antiglutamatergic and GABAergic facilitating properties, was evaluated in a wide range of animals and experimental protocols against OP poisoning. Its remarkable efficacy against OP exposure was established both in prophylactic and post-exposure therapies in both small and large animals. The present review will highlight the outstanding neuroprotective effect of caramiphen as the optimal candidate for the treatment of OP-exposed subjects.

Chronic behavioral and cognitive deficits in a rat survival model of paraoxon toxicity

Organophosphate (OP) compounds, including paraoxon (POX), are similar to nerve agents such as sarin. There is a growing concern that OP agents could be weaponized to cause mass civilian causalities. We have developed a rodent survival model of POX toxicity that is being used to evaluate chronic morbidity and to screen for medical countermeasures against severe OP exposure. It is well known that the survivors of nerve gas and chronic OP exposure exhibit neurobehavioral deficits such as mood changes, depression, and memory impairments. In this study we investigated whether animals surviving severe POX exposure exhibited long-term neurological impairments. POX exposure produced overt signs of cholinergic toxicity. Rats were rescued using an optimized atropine, 2-PAM and diazepam therapy. Surviving rats were studied using established behavioral assays for identifying symptoms of depression and memory impairment 3-months after POX exposure. In the forced swim test, POX rats exhibited increased immobility time indicative of a despair-like state. In the sucrose preference test, POX rats consumed significantly less sucrose water indicating anhedonia-like condition. POX rats also displayed increased anxiety as characterized by significantly lower performance in the open arm of the elevated plus maze. Further, when tested with a novel object recognition paradigm, POX rats exhibited a negative discrimination ratio indicative of impaired recognition memory. The results indicate that this model of survival from severe POX exposure can be employed to study some of the molecular bases for OP-induced chronic behavioral and cognitive comorbidities and develop therapies for their treatment.

Inhibitors of acetylcholinesterase and butyrylcholinesterase meet immunity

Acetylcholinesterase (AChE) inhibitors are widely used for the symptomatic treatment of Alzheimer’s disease and other dementias. More recent use is for myasthenia gravis. Many of these inhibitors interact with the second known cholinesterase, butyrylcholinesterase (BChE). Further, evidence shows that acetylcholine plays a role in suppression of cytokine release through a “cholinergic anti-inflammatory pathway” which raises questions about the role of these inhibitors in the immune system. This review covers research and discussion of the role of the inhibitors in modulating the immune response using as examples the commonly available drugs, donepezil, galantamine, huperzine, neostigmine and pyridostigmine. Major attention is given to the cholinergic anti-inflammatory pathway, a well-described link between the central nervous system and terminal effector cells in the immune system.

Development of status epilepticus, sustained calcium elevations and neuronal injury in a rat survival model of lethal paraoxon intoxication

Paraoxon (POX) is an active metabolite of organophosphate (OP) pesticide parathion that has been weaponized and used against civilian populations. Exposure to POX produces high mortality. OP poisoning is often associated with chronic neurological disorders. In this study, we optimize a rat survival model of lethal POX exposures in order to mimic both acute and long-term effects of POX intoxication. Male Sprague-Dawley rats injected with POX (4mg/kg, ice-cold PBS, s.c.) produced a rapid cholinergic crisis that evolved into status epilepticus (SE) and death within 6-8min. The EEG profile for POX induced SE was characterized and showed clinical and electrographic seizures with 7-10Hz spike activity. Treatment of 100% lethal POX intoxication with an optimized three drug regimen (atropine, 2mg/kg, i.p., 2-PAM, 25mg/kg, i.m. and diazepam, 5mg/kg, i.p.) promptly stopped SE and reduced acute mortality to 12% and chronic mortality to 18%. This model is ideally suited to test effective countermeasures against lethal POX exposure. Animals that survived the POX SE manifested prolonged elevations in hippocampal [Ca(2+)]i (Ca(2+) plateau) and significant multifocal neuronal injury. POX SE induced Ca(2+) plateau had its origin in Ca(2+) release from intracellular Ca(2+) stores since inhibition of ryanodine/IP3 receptor lowered elevated Ca(2+) levels post SE. POX SE induced neuronal injury and alterations in Ca(2+) dynamics may underlie some of the long term morbidity associated with OP toxicity.

Serotonin 1A receptor inhibits the status epilepticus induced by lithium-pilocarpine in rats

Status epilepticus (SE) is a life-threatening neurological emergency associated with a high mortality rate. The serotonin 1A (5-HT1A) receptor is a possible target for the treatment of SE, but its role in animal models and the precise area of brain involved remain controversial. The hippocampus is a candidate site due to its key role in the development of SE and the existence of a high density of 5-HT1A receptors. Therefore, we investigated the effects of subcutaneous and intrahippocampal activation of 5-HT1A receptors in lithium-pilocarpine-induced SE, and tested whether the hippocampus is a true effector site. We developed SE in male Sprague-Dawley rats by giving lithium chloride (LiCl; 3 meq/kg, i.p.) 22-24 h prior to pilocarpine (25 mg/kg, i.p.), and found that 8-OH-DPAT, a 5-HT1A receptor agonist administered subcutaneously (s.c.) at 0.5 or 1.0 mg/kg 1 h before pilocarpine injection increased the latency to the first epileptiform spikes, the electrographic SE, and the behavioral generalized seizures (GS), while reducing the total EEG seizure time (P <0.01). The duration of GS was shortened only by 1.0 mg/kg 8-OH-DPAT s.c. (P <0.05). All these effects were inhibited by combined administration of WAY-100635 (1.0 mg/kg, s.c.) (P <0.05), an antagonist of the 5-HT1A receptor, but WAY-100635 alone and low doses of 8-OHDPAT (0.01 and 0.1 mg/kg) did not alter seizure activity. Furthermore, intrahippocampal 8-OH-DPAT only shortened the GS duration (P <0.05). These findings imply that the 5-HT1A receptor is a promising therapeutic target against the generation and propagation of SE, and hippocampal receptors are involved in reducing the seizure severity.

Autism: metabolism, mitochondria, and the microbiome

New approaches are needed to examine the diverse symptoms and comorbidities of the growing family of neurodevelopmental disorders known as autism spectrum disorder (ASD). ASD originally was thought to be a static, inheritable neurodevelopmental disorder, and our understanding of it is undergoing a major shift. It is emerging as a dynamic system of metabolic and immune anomalies involving many organ systems, including the brain, and environmental exposure. The initial detailed observation and inquiry of patients with ASD and related conditions and the histories of their caregivers and families have been invaluable. How gastrointestinal (GI) factors are related to ASD is not yet clear. Nevertheless, many patients with ASD have a history of previous antibiotic exposure or hospitalization, GI symptoms, abnormal food cravings, and unique intestinal bacterial populations, which have been proposed to relate to variable symptom severity. In addition to traditional scientific inquiry, detailed clinical observation and recording of exacerbations, remissions, and comorbidities are needed. This article reviews the role that enteric short-chain fatty acids, particularly propionic (also called propanoic) acid, produced from ASD-associated GI bacteria, may play in the etiology of some forms of ASD. Human populations that are partial metabolizers of propionic acid are more common than previously thought. The results from pre-clinical laboratory studies show that propionic acid-treated rats display ASD-like repetitive, perseverative, and antisocial behaviors and seizure. Neurochemical changes, consistent and predictive with findings in ASD patients, including neuroinflammation, increased oxidative stress, mitochondrial dysfunction, glutathione depletion, and altered phospholipid/acylcarnitine profiles, have been observed. Propionic acid has bioactive effects on (1) neurotransmitter systems, (2) intracellular acidification and calcium release, (3) fatty acid metabolism, (4) gap junction gating, (5) immune function, and (6) alteration of gene expression that warrant further exploration. Traditional scientific experimentation is needed to verify the hypothesis that enteric short-chain fatty acids may be a potential environmental trigger in some forms of ASD. Novel collaborative developments in systems biology, particularly examining the role of the microbiome and its effects on host metabolism, immune and mitochondrial function, and gene expression, hold great promise in ASD.

HI-6 modulates immunization efficacy in a BALB/c mouse model

HI-6 is used as an antidote to nerve agents. It can also act as an antagonist to acetylcholine receptors (AChRs) including the nicotinic receptor, α 7 nAChR which is involved in regulating the immune response through macrophages. This experiment investigated the efficacy of HI-6 to regulate the immune response. Laboratory BALB/c mice received HI-6 and/or keyhole limpet hemocyanin (KLH) as an antigen. Antibody production was investigated after either 21 or 65 days when either single or repeated dose of antigen was applied. We confirmed that HI-6 significantly improved vaccination efficacy when KLH was given in a dose of 1mg/kg. The effect was dose dependent. A combination of HI-6 and KLH produced a vaccination of almost the same efficacy as that for Freund's complete adjuvant. The findings point at the suitability of HI-6 for improving vaccination efficacy at the level of immunity regulation by the nervous system.

An acetylcholinesterase-based chronoamperometric biosensor for fast and reliable assay of nerve agents

The enzyme acetylcholinesterase (AChE) is an important part of cholinergic nervous system, where it stops neurotransmission by hydrolysis of the neurotransmitter acetylcholine. It is sensitive to inhibition by organophosphate and carbamate insecticides, some Alzheimer disease drugs, secondary metabolites such as aflatoxins and nerve agents used in chemical warfare. When immobilized on a sensor (physico-chemical transducer), it can be used for assay of these inhibitors. In the experiments described herein, an AChE- based electrochemical biosensor using screen printed electrode systems was prepared. The biosensor was used for assay of nerve agents such as sarin, soman, tabun and VX. The limits of detection achieved in a measuring protocol lasting ten minutes were 7.41 × 10⁻¹² mol/L for sarin, 6.31 × 10⁻¹² mol/L for soman, 6.17 × 10⁻¹¹ mol/L for tabun, and 2.19 × 10⁻¹¹ mol/L for VX, respectively. The assay was reliable, with minor interferences caused by the organic solvents ethanol, methanol, isopropanol and acetonitrile. Isopropanol was chosen as suitable medium for processing lipophilic samples.

Role of hormones and neurosteroids in epileptogenesis

This article describes the emerging evidence of hormonal influence on epileptogenesis, which is a process whereby a brain becomes progressively epileptic due to an initial precipitating event of diverse origin such as brain injury, stroke, infection, or prolonged seizures. The molecular mechanisms underlying the development of epilepsy are poorly understood. Neuroinflammation and neurodegeneration appear to trigger epileptogenesis. There is an intense search for drugs that truly prevent the development of epilepsy in people at risk. Hormones play an important role in children and adults with epilepsy. Corticosteroids, progesterone, estrogens, and neurosteroids have been shown to affect seizure activity in animal models and in clinical studies. However, the impact of hormones on epileptogenesis has not been investigated widely. There is emerging new evidence that progesterone, neurosteroids, and endogenous hormones may play a role in regulating the epileptogenesis. Corticosterone has excitatory effects and triggers epileptogenesis in animal models. Progesterone has disease-modifying activity in epileptogenic models. The antiepileptogenic effect of progesterone has been attributed to its conversion to neurosteroids, which binds to GABA-A receptors and enhances phasic and tonic inhibition in the brain. Neurosteroids are robust anticonvulsants. There is pilot evidence that neurosteroids may have antiepileptogenic properties. Future studies may generate new insight on the disease-modifying potential of hormonal agents and neurosteroids in epileptogenesis.

Treatment of status epilepticus with ketamine, are we there yet?

Status epilepticus (SE), a neurological emergency both in adults and in children, could lead to brain damage and even death if untreated. Generalized convulsive SE (GCSE) is the most common and severe form, an example of which is that induced by organophosphorus nerve agents. First- and second-line pharmacotherapies are relatively consensual, but if seizures are still not controlled, there is currently no definitive data to guide the optimal choice of therapy. The medical community seems largely reluctant to use ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate glutamate receptor. However, a review of the literature clearly shows that ketamine possesses, in preclinical studies, antiepileptic properties and provides neuroprotection. Clinical evidences are scarcer and more difficult to analyze, owing to a use in situations of polytherapy. In absence of existing or planned randomized clinical trials, the medical community should make up its mind from well-conducted preclinical studies performed on appropriate models. Although potentially active, ketamine has no real place for the treatment of isolated seizures, better accepted drugs being used. Its best usage should be during GCSE, but not waiting for SE to become totally refractory. Concerns about possible developmental neurotoxicity might limit its pediatric use for refractory SE.