Effects of HI 6, diazepam and atropine on soman-induced IL-1 beta protein in rat brain

Neurotoxicity evoked by organophosphates and available countermeasures

Organophosphorus compounds (OP) are a constant problem, both in the military and in the civilian field, not only in the form of acute poisoning but also for their long-lasting consequences. No antidote has been found that satisfactorily protects against the toxic effects of organophosphates. Likewise, there is no universal cure to avert damage after poisoning. The key mechanism of organophosphate toxicity is the inhibition of acetylcholinesterase. The overstimulation of nicotinic or muscarinic receptors by accumulated acetylcholine on a synaptic cleft leads to activation of the glutamatergic system and the development of seizures. Further consequences include generation of reactive oxygen species (ROS), neuroinflammation, and the formation of various other neuropathologists. In this review, we present neuroprotection strategies which can slow down the secondary nerve cell damage and alleviate neurological and neuropsychiatric disturbance. In our opinion, there is no unequivocal approach to ensure neuroprotection, however, sooner the neurotoxicity pathway is targeted, the better the results which can be expected. It seems crucial to target the key propagation pathways, i.e., to block cholinergic and, foremostly, glutamatergic cascades. Currently, the privileged approach oriented to stimulating GABA_AR by benzodiazepines is of limited efficacy, so that antagonizing the hyperactivity of the glutamatergic system could provide an even more efficacious approach for terminating OP-induced seizures and protecting the brain from permanent damage. Encouraging results have been reported for tezampanel, an antagonist of GluK1 kainate and AMPA receptors, especially in combination with caramiphen, an anticholinergic and anti-glutamatergic agent. On the other hand, targeting ROS by antioxidants cannot or already developed neuroinflammation does not seem to be very productive as other processes are also involved.

Evaluating mice lacking serum carboxylesterase as a behavioral model for nerve agent intoxication

Mice and other rodents are typically utilized for chemical warfare nerve agent research. Rodents have large amounts of carboxylesterase in their blood, while humans do not. Carboxylesterase nonspecifically binds to and detoxifies nerve agent. The presence of this natural bioscavenger makes mice and other rodents poor models for studies identifying therapeutics to treat humans exposed to nerve agents. To obviate this problem, a serum carboxylesterase knockout (Es1 KO) mouse was created. In this study, Es1 KO and wild type (WT) mice were assessed for differences in gene expression, nerve agent (soman; GD) median lethal dose (MLD) values, and behavior prior to and following nerve agent exposure. No expression differences were detected between Es1 KO and WT mice in more than 34 000 mouse genes tested. There was a significant difference between Es1 KO and WT mice in MLD values, as the MLD for GD-exposed WT mice was significantly higher than the MLD for GD-exposed Es1 KO mice. Behavioral assessments of Es1 KO and WT mice included an open field test, a zero maze, a Barnes maze, and a sucrose preference test (SPT). While sex differences were observed in various measures of these tests, overall, Es1 KO mice behaved similarly to WT mice. The two genotypes also showed virtually identical neuropathological changes following GD exposure. Es1 KO mice appear to have an enhanced susceptibility to GD toxicity while retaining all other behavioral and physiological responses to this nerve agent, making the Es1 KO mouse a more human-like model for nerve agent research.

Arsenic and dichlorvos: Possible interaction between two environmental contaminants

Metals are ubiquitously present in the environment and pesticides are widely used throughout the world. Environmental and occupational exposure to metal along with pesticide is an area of great concern to both the public and regulatory authorities. Our major concern is that combination of these toxicant present in environment may elicit toxicity either due to additive or synergistic interactions or 'joint toxic actions' among these toxicants. It poses a rising threat to human health. Water contamination particularly ground water contamination with arsenic is a serious problem in today's scenario since arsenic is associated with several kinds of health problems, such arsenic associated health anomalies are commonly called as 'Arsenism'. Uncontrolled use and spillage of pesticides into the environment has resulted in alarming situation. Moreover serious concerns are being addressed due to their persistence in the environmental matrices such as air, soil and surface water runoff resulting in continuous exposure of these harmful chemicals to human beings and animals. Bio-availability of these environmental toxicants has been enhanced much due to anthropological activities. Dreadfully very few studies are available on combined exposures to these toxicants on the animal or human system. Studies on the acute and chronic exposure to arsenic and DDVP are well reported and well defined. Arsenic is a common global ground water contaminant while dichlorvos is one of the most commonly and widely employed organophosphate based insecticide used in agriculture, horticulture etc. There is thus a real situation where a human may get exposed to these toxicants while working in a field. This review highlights the individual and combined exposure to arsenic and dichlorvos on health.

Neuroprotective mechanisms activated in non-seizing rats exposed to sarin

Exposure to organophosphate (OP) nerve agents, such as sarin, may lead to uncontrolled seizures and irreversible brain injury and neuropathology. In rat studies, a median lethal dose of sarin leads to approximately half of the animals developing seizures. Whereas previous studies analyzed transcriptomic effects associated with seizing sarin-exposed rats, our study focused on the cohort of sarin-exposed rats that did not develop seizures. We analyzed the genomic changes occurring in sarin-exposed, non-seizing rats and compared differentially expressed genes and pathway activation to those of seizing rats. At the earliest time point (0.25 h) and in multiple sarin-sensitive brain regions, defense response genes were commonly expressed in both groups of animals as compared to the control groups. All sarin-exposed animals activated the MAPK signaling pathway, but only the seizing rats activated the apoptotic-associated JNK and p38 MAPK signaling sub-pathway. A unique phenotype of the non-seizing rats was the altered expression levels of genes that generally suppress inflammation or apoptosis. Importantly, the early transcriptional response for inflammation- and apoptosis-related genes in the thalamus showed opposite trends, with significantly down-regulated genes being up-regulated, and vice versa, between the seizing and non-seizing rats. These observations lend support to the hypothesis that regulation of anti-inflammatory genes might be part of an active and sufficient response in the non-seizing group to protect against the onset of seizures. As such, stimulating or activating these responses via pretreatment strategies could boost resilience against nerve agent exposures.

Perspectives on neuroinflammation and excitotoxicity: a neurotoxic conspiracy?

Emerging evidences underline the ability of several environmental contaminants to induce an inflammatory response within the central nervous system, named neuroinflammation. This can occur as a consequence of a direct action of the neurotoxicant to the CNS and/or as a response secondary to the activation of the peripheral inflammatory response. In both cases, neuroinflammation is driven by the release of several soluble factors among which pro-inflammatory cytokines. IL-1β and TNF-α have been extensively studied for their effects within the CNS and emerged for their role in the modulation of the neuronal response, which allow the immune response to integrate with specific neuronal functions, as neurotransmission and synaptic plasticity. In particular, it has been evidenced a potential detrimental link between these cytokines and the glutamatergic system that seems to be part of increased brain excitability and excitotoxicity occurring in different pathological conditions. Aim of this mini-review will be to present experimental evidence on the way IL-1β and TNF-α impact neurons, focusing on the glutamatergic signalling, to provide a perspective on novel pathways possibly involved in environmental contaminants neurotoxicity.

Combinations of ketamine and atropine are neuroprotective and reduce neuroinflammation after a toxic status epilepticus in mice

Epileptic seizures and status epilepticus (SE) induced by the poisoning with organophosphorus nerve agents (OP), like soman, are accompanied by neuroinflammation whose role in seizure-related brain damage (SRBD) is not clear. Antagonists of the NMDA glutamate ionotropic receptors are currently among the few compounds able to arrest seizures and provide neuroprotection even during refractory status epilepticus (RSE). Racemic ketamine (KET), in combination with atropine sulfate (AS), was previously shown to counteract seizures and SRBD in soman-poisoned guinea-pigs. In a mouse model of severe soman-induced SE, we assessed the potentials of KET/AS combinations as a treatment for SE/RSE-induced SRBD and neuroinflammation. When starting 30min after soman challenge, a protocol involving six injections of a sub-anesthetic dose of KET (25mg/kg) was evaluated on body weight loss, brain damage, and neuroinflammation whereas during RSE, anesthetic protocols were considered (KET 100mg/kg). After confirming that during RSE, KET injection was to be repeated despite some iatrogenic deaths, we used these proof-of-concept protocols to study the changes in mRNA and related protein contents of some inflammatory cytokines, chemokines and adhesion molecules in cortex and hippocampus 48h post-challenge. In both cases, the KET/AS combinations showed important neuroprotective effects, suppressed neutrophil granulocyte infiltration and partially suppressed glial activation. KET/AS could also reduce the increase in mRNA and related pro-inflammatory proteins provoked by the poisoning. In conclusion, the present study confirms that KET/AS treatment has a strong potential for SE/RSE management following OP poisoning. The mechanisms involved in the reduction of central neuroinflammation remain to be studied.

Transcriptional analysis of rat piriform cortex following exposure to the organophosphonate anticholinesterase sarin and induction of seizures

Background

Organophosphorus nerve agents irreversibly inhibit acetylcholinesterase, causing a toxic buildup of acetylcholine at muscarinic and nicotinic receptors. Current medical countermeasures to nerve agent intoxication increase survival if administered within a short period of time following exposure but may not fully prevent neurological damage. Therefore, there is a need to discover drug treatments that are effective when administered after the onset of seizures and secondary responses that lead to brain injury.

Methods

To determine potential therapeutic targets for such treatments, we analyzed gene expression changes in the rat piriform cortex following sarin (O-isopropyl methylphosphonofluoridate)-induced seizure. Male Sprague-Dawley rats were challenged with 1 × LD₅₀ sarin and subsequently treated with atropine sulfate, 2-pyridine aldoxime methylchloride (2-PAM), and the anticonvulsant diazepam. Control animals received an equivalent volume of vehicle and drug treatments. The piriform cortex, a brain region particularly sensitive to neural damage from sarin-induced seizures, was extracted at 0.25, 1, 3, 6, and 24 h after seizure onset, and total RNA was processed for microarray analysis. Principal component analysis identified sarin-induced seizure occurrence and time point following seizure onset as major sources of variability within the dataset. Based on these variables, the dataset was filtered and analysis of variance was used to determine genes significantly changed in seizing animals at each time point. The calculated p-value and geometric fold change for each probeset identifier were subsequently used for gene ontology analysis to identify canonical pathways, biological functions, and networks of genes significantly affected by sarin-induced seizure over the 24-h time course.

Results

A multitude of biological functions and pathways were identified as being significantly altered following sarin-induced seizure. Inflammatory response and signaling pathways associated with inflammation were among the most significantly altered across the five time points examined.

Conclusions

This analysis of gene expression changes in the rat brain following sarin-induced seizure and the molecular pathways involved in sarin-induced neurodegeneration will facilitate the identification of potential therapeutic targets for the development of effective neuroprotectants to treat nerve agent exposure.

Transcriptional responses of the nerve agent-sensitive brain regions amygdala, hippocampus, piriform cortex, septum, and thalamus following exposure to the organophosphonate anticholinesterase sarin

Background

Although the acute toxicity of organophosphorus nerve agents is known to result from acetylcholinesterase inhibition, the molecular mechanisms involved in the development of neuropathology following nerve agent-induced seizure are not well understood. To help determine these pathways, we previously used microarray analysis to identify gene expression changes in the rat piriform cortex, a region of the rat brain sensitive to nerve agent exposure, over a 24-h time period following sarin-induced seizure. We found significant differences in gene expression profiles and identified secondary responses that potentially lead to brain injury and cell death. To advance our understanding of the molecular mechanisms involved in sarin-induced toxicity, we analyzed gene expression changes in four other areas of the rat brain known to be affected by nerve agent-induced seizure (amygdala, hippocampus, septum, and thalamus).

Methods

We compared the transcriptional response of these four brain regions to sarin-induced seizure with the response previously characterized in the piriform cortex. In this study, rats were challenged with 1.0 × LD₅₀ sarin and subsequently treated with atropine sulfate, 2-pyridine aldoxime methylchloride, and diazepam. The four brain regions were collected at 0.25, 1, 3, 6, and 24 h after seizure onset, and total RNA was processed for microarray analysis.

Results

Principal component analysis identified brain region and time following seizure onset as major sources of variability within the dataset. Analysis of variance identified genes significantly changed following sarin-induced seizure, and gene ontology analysis identified biological pathways, functions, and networks of genes significantly affected by sarin-induced seizure over the 24-h time course. Many of the molecular functions and pathways identified as being most significant across all of the brain regions were indicative of an inflammatory response. There were also a number of molecular responses that were unique for each brain region, with the thalamus having the most distinct response to nerve agent-induced seizure.

Conclusions

Identifying the molecular mechanisms involved in sarin-induced neurotoxicity in these sensitive brain regions will facilitate the development of novel therapeutics that can potentially provide broad-spectrum protection in five areas of the central nervous system known to be damaged by nerve agent-induced seizure.

The acute phase response and soman-induced status epilepticus: temporal, regional and cellular changes in rat brain cytokine concentrations

Background

Neuroinflammation occurs following brain injury, including soman (GD) induced status epilepticus (SE), and may contribute to loss of neural tissue and declined behavioral function. However, little is known about this important pathological process following GD exposure. Limited transcriptional information on a small number of brain-expressed inflammatory mediators has been shown following GD-induced SE and even less information on protein upregulation has been elucidated. The purpose of this study is to further characterize the regional and temporal progression of the neuroinflammatory process following acute GD-induced SE.

Methods

The protein levels of 10 cytokines was quantified using bead multiplex immunoassays in damaged brain regions (i.e., piriform cortex, hippocampus and thalamus) up to 72 hours following seizure onset. Those factors showing significant changes were then localized to neural cells using fluorescent IHC.

Results

A significant concentration increase was observed in all injured brain regions for four acute phase response (APR) induction cytokines: interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor (TNF)-α. Increases in these APR cytokines corresponded both temporally and regionally to areas of known seizure damage and neuronal death. Neurotoxic cytokines IL-1α and IL-1β were primarily expressed by activated microglia whereas the potentially neuroprotective cytokine IL-6 was expressed by neurons and hypertrophic astrocytes.

Conclusions

Increases in neurotoxic cytokines likely play an active role in the progression of GD-induced SE neuropathology though the exact role that these and other cytokines play in this process require further study.

Gene expression profiling of rat hippocampus following exposure to the acetylcholinesterase inhibitor soman

Soman (O-pinacolyl methylphosphonofluoridate) is a potent neurotoxicant. Acute exposure to soman causes acetylcholinesterase inhibition, resulting in excessive levels of acetylcholine. Excessive acetylcholine levels cause convulsions, seizures, and respiratory distress. The initial cholinergic crisis can be overcome by rapid anticholinergic therapeutic intervention, resulting in increased survival. However, conventional treatments do not protect the brain from seizure-related damage, and thus, neurodegeneration of soman-sensitive brain areas is a potential postexposure outcome. We performed gene expression profiling of the rat hippocampus following soman exposure to gain greater insight into the molecular pathogenesis of soman-induced neurodegeneration. Male Sprague-Dawley rats were pretreated with the oxime HI-6 (l-(((4-aminocarbonyl)pyridinio)methoxyl)methyl)-2-((hydroxyimino)methyl)-pyridinium dichloride; 125 mg/kg, ip) 30 min prior to challenge with soman (180 microg/kg, sc). One minute after soman challenge, animals were treated with atropine methyl nitrate (2.0 mg/kg, im). Hippocampi were harvested 1, 3, 6, 12, 24, 48, 72, 96, and 168 h after soman exposure and RNA extracted to generate microarray probes for gene expression profiling. Principal component analysis of the microarray data revealed a progressive alteration in gene expression profiles beginning 1 h postexposure and continuing through 24 h postexposure. At 48 h to 168 h postexposure, the gene expression profiles clustered nearer to controls but did not completely return to control profiles. On the basis of the principal component analysis, analysis of variance was used to identify the genes most significantly changed as a result of soman at each postexposure time point. To gain insight into the biological relevance of these gene expression changes, genes were rank ordered by p-value and categorized using gene ontology-based algorithms into biological functions, canonical pathways, and gene networks significantly affected by soman. Numerous signaling and inflammatory pathways were identified as perturbed by soman. These data provide important insights into the molecular pathways involved in soman-induced neuropathology and a basis for generating hypotheses about the mechanism of soman-induced neurodegeneration.

The role of interleukin-1 in seizures and epilepsy: a critical review

Interleukin-1 (IL-1) has a multitude of functions in the central nervous system. Some of them involve mechanisms that are related to epileptogenesis. The role of IL-1 in seizures and epilepsy has been investigated in both patients and animal models. This review aims to synthesize, based on the currently available literature, the consensus role of IL-1 in epilepsy. Three lines of evidence suggest a role for IL-1: brain tissue from epilepsy patients and brain tissue from animal models shows increased IL-1 expression after seizures, and IL-1 has proconvulsive properties when applied exogeneously. However, opposing results have been published as well. More research is needed to fully establish the role of IL-1 in seizure generation and epilepsy, and to explore possible new treatment strategies that are based on interference with intracellular signaling cascades that are initiated when IL-1 binds to its receptor.

Seizure duration following sarin exposure affects neuro-inflammatory markers in the rat brain

The current study was aimed to characterize for the first time the alterations in the characteristic neuro-inflammatory markers triggered by sarin exposure in the rat's brain, and to investigate its dependency on seizure duration. Centrally mediated seizures are a common consequence of exposure to organophosphates (OP) despite conventional treatment with atropine and an oxime. In the present study midazolam, was used to control duration and intensity of seizures. The levels of the pro-inflammatory cytokine peptides IL-1beta, IL-6, TNF-alpha and prostaglandin E2 (PGE2) were monitored at various times after sarin exposure in the hippocampus and cortex of rats treated with midazolam following 5 or 30 min of seizure activity. Biochemical evaluation of brain tissues revealed a significant increase in the level of the pro-inflammatory peptides starting at 2 h and peaking at 2-24 h following sarin. Hippocampal values of IL1-beta increased from 1.2+/-0.1 pg/mg tissue (control), to 2.4+/-0.3 at 2 h (5 min seizure) and to 9.3+/-2.5 at 8h (30 min seizure). PGE2 level in the hippocampus increased up to 24 h following exposure (from 56+/-3 to 175+/-26 and 277+/-28 pg/mg tissue) following 5 and 30 min of seizure activity respectively. Thus, unlike limitation of seizures to 5 min by midazolam, delayed treatment (30 min) resulted in prolonged seizures and pronounced increase in cytokines and PGE2. In addition, a second increase in inflammatory markers was observed 30 days following sarin exposure only in rats treated following 30 min of seizure activity. Histological evaluation of the rat brain, conducted in this study, revealed lack of damage in the hippocampus and piriform cortex with minor lateral ventricles enlargement in few animals following 5 min of sarin-induced seizure activity. In contrast, marked histological damage to the brain was demonstrated following 30 min of seizure activity, consisting severe damage to the hippocampus, piriform cortex and some thalamic nuclei. In summary, a novel characterization of the prolonged central neuro-inflammatory process that accompanies sarin exposure is presented. The timing of the anticonvulsive treatment was shown to be crucial in modulation of the neuro-inflammatory response, and may implicate the consequent long-term brain damage.

In vitro and in vivo evaluation of pyridinium oximes: mode of interaction with acetylcholinesterase, effect on tabun- and soman-poisoned mice and their cytotoxicity

The increased concern about terrorist use of nerve agents prompted us to search for new more effective oximes against tabun and soman poisoning. We investigated the interactions of five bispyridinium oximes: K027 [1-(4-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium) propane dibromide], K048 [1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide], K033 [1,4-bis(2-hydroxyiminomethylpyridinium) butane dibromide], TMB-4 [1,3-bis(4-hydroxyiminomethylpyridinium) propane dibromide] and HI-6 [(1-(2-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium)-2-oxapropane dichloride)] with human erythrocyte acetylcholinesterase (AChE; E.C. 3.1.1.7) and their effects on tabun- and soman-poisoned mice. All the oximes reversibly inhibited AChE, and the enzyme-oxime dissociation constants were between 17 and 180 microM. Tabun-inhibited AChE was completely reactivated by TMB-4, K027 and K048, with the overall reactivation rate constants of 306, 376 and 673 min(-1)M(-1), respectively. The reactivation of tabun-inhibited AChE by K033 reached 50% after 24h, while HI-6 failed to reactivate any AChE at all. Soman-inhibited AChE was resistant to reactivation by 1mM oximes. All studied oximes protected AChE from phosphorylation with both soman and tabun. In vivo experiments showed that the studied oximes were relatively toxic to mice; K033 was the most toxic (LD50=33.4 mg/kg), while K027 was the least toxic (LD50=672.8 mg/kg). The best antidotal efficacy was obtained with K048, K027 and TMB-4 for tabun poisoning, and HI-6 for soman poisoning. Moreover, all tested oximes showed no cytotoxic effect on several cell lines in concentrations up to 0.8mM. The potency of the oximes K048 and K027 to protect mice from five-fold LD50 of tabun and their low toxicity make these compounds leading in the therapy of tabun poisoning. The combination of HI-6 and atropine is the therapy of choice for soman poisoning.