LD50 Soman Research Articles

Sex-based structural and functional MRI outcomes in the rat brain after soman (GD) exposure-induced status epilepticus.

Exposure to the nerve agent, soman (GD), induces status epilepticus (SE), epileptogenesis, and even death. Although rodent models studying the pathophysiological mechanisms show females to be more reactive to soman, no tangible sex differences in brains postexposure have been reported. In this study, we used multimodal imaging using MRI in adult rats to determine potential sex-based biomarkers of soman effects. Male and female Sprague Dawley rats were challenged with 1.2 × LD50 soman followed by medical countermeasures. Ten weeks later, the brains were analyzed via structural and functional MRI. Despite no significant sex differences in the initial SE severity after soman exposure, long-term MRI-based structural and functional differences were evident in the brains of both sexes. While T2 MRI showed lesser soman-induced neurodegeneration, large areas of T1 enhancements occurred in females than in males, indicating a distinct pathophysiology unrelated to neurodegeneration. fMRI-based resting-state functional connectivity (RSFC), indicated greater reductions in soman-exposed females than in males, associating with the T1 enhancements (unrelated to neurodegeneration) rather than T2-hyperintensity or T1-hypointensity (representing neurodegeneration). The wider T1 enhancements associating with the decreased spontaneous neuronal activity in multiple resting-state networks in soman-exposed females than males suggest that neural changes unrelated to cellular atrophy impinge on brain function postexposure. Taken together with lower spontaneous neural activity in soman-exposed females, the results indicate some form of neuroprotective state that was not present in males. The results indicate that endpoints other than neurodegeneration may need to be considered to translate sex-based nerve agent effects in humans.

Oral Pretreatment with Galantamine Effectively Mitigates the Acute Toxicity of a Supralethal Dose of Soman in Cynomolgus Monkeys Posttreated with Conventional Antidotes.

Earlier reports suggested that galantamine, a drug approved to treat mild-to-moderate Alzheimer's disease (AD), and other centrally acting reversible acetylcholinesterase (AChE) inhibitors can serve as adjunct pretreatments against poisoning by organophosphorus compounds, including the nerve agent soman. The present study was designed to determine whether pretreatment with a clinically relevant oral dose of galantamine HBr mitigates the acute toxicity of 4.0×LD50 soman (15.08 µg/kg) in Macaca fascicularis posttreated intramuscularly with the conventional antidotes atropine (0.4 mg/kg), 2-pyridine aldoxime methyl chloride (30 mg/kg), and midazolam (0.32 mg/kg). The pharmacokinetic profile and maximal degree of blood AChE inhibition (∼25%-40%) revealed that the oral doses of 1.5 and 3.0 mg/kg galantamine HBr in these nonhuman primates (NHPs) translate to human-equivalent doses that are within the range used for AD treatment. Subsequent experiments demonstrated that 100% of NHPs pretreated with either dose of galantamine, challenged with soman, and posttreated with conventional antidotes survived 24 hours. By contrast, given the same posttreatments, 0% and 40% of the NHPs pretreated, respectively, with vehicle and pyridostigmine bromide (1.2 mg/kg, oral), a peripherally acting reversible AChE inhibitor approved as pretreatment for military personnel at risk of exposure to soman, survived 24 hours after the challenge. In addition, soman caused extensive neurodegeneration in the hippocampi of saline- or pyridostigmine-pretreated NHPs, but not in the hippocampi of galantamine-pretreated animals. To our knowledge, this is the first study to demonstrate the effectiveness of clinically relevant oral doses of galantamine to prevent the acute toxicity of supralethal doses of soman in NHPs. SIGNIFICANCE STATEMENT: This is the first study to demonstrate that a clinically relevant oral dose of galantamine effectively prevents lethality and neuropathology induced by a supralethal dose of the nerve agent soman in Cynomolgus monkeys posttreated with conventional antidotes. These findings are of major significance for the continued development of galantamine as an adjunct pretreatment against nerve agent poisoning.

Electroencephalographic analysis in soman-exposed 21-day-old rats and the effects of midazolam or LY293558 with caramiphen.

Acute nerve agent exposure induces status epilepticus (SE), which can cause brain damage or death. Research aiming at developing effective therapies for controlling nerve agent-induced SE is commonly performed in adult rats. The characteristics of nerve agent-induced SE in young rats are less clear; relevant knowledge is necessary for developing effective pediatric therapies. Here, we have used electroencephalographic (EEG) recordings and analysis to study seizures in postnatal day 21 rats exposed to 1.2 × LD50 of soman, and compared the antiseizure efficacy of midazolam (MDZ)-currently considered by the Food and Drug Administration to replace diazepam for treating SE in victims of nerve agent exposure-with that of LY293558, an AMPA/GluK1 receptor antagonist, administered in combination with caramiphen, an antimuscarinic with N-methyl-d-aspartate receptor antagonistic properties. Prolonged SE developed in 80% of the rats and was reflected in behavioral seizures/convulsions. Both MDZ and LY293558+ caramiphen stopped the SE induced by soman, but there was a significant recurrence of seizures within 24 h postexposure only in the MDZ-treated group, as revealed in the raw EEG data and their representation in the frequency domain using a fast Fourier transform and in spectral analysis over 24 hours. In contrast to the high efficacy of LY293558 + caramiphen, MDZ is not an effective treatment for SE induced by soman in young animals.

Full Protection Against Soman-Induced Seizures and Brain Damage by LY293558 and Caramiphen Combination Treatment in Adult Rats.

Acute exposure to nerve agents induces status epilepticus (SE), which causes brain damage or death. LY293558, an antagonist of AMPA and GluK1 kainate receptors is a very effective anticonvulsant and neuroprotectant against soman; however, some neuronal damage is still present after treatment of soman-exposed rats with LY293558. Here, we have tested whether combining LY293558 with an NMDA receptor antagonist can eliminate the residual damage. For this purpose, we chose caramiphen (CRM), an antimuscarinic compound with NMDA receptor antagonistic properties. Adult male rats were exposed to 1.2 × LD50 soman, and at 20min after soman exposure, were injected with atropine + HI-6, or atropine + HI-6 + LY293558 (15mg/kg), or atropine + HI-6 + LY293558 + CRM (50mg/kg). We found that (1) the LY293558 + CRM treatment terminated SE significantly faster than LY293558 alone; (2) after cessation of the initial SE, seizures did not return in the LY293558 + CRM-treated group, during 72h of monitoring; (3) power spectrum analysis of continuous EEG recordings for 7days post-exposure showed increased delta and decreased gamma power that lasted beyond 24h post-exposure only in the rats who did not receive anticonvulsant treatment; (4) spontaneous recurrent seizures appeared on day 7 only in the group that did not receive anticonvulsant treatment; (5) significant neuroprotection was achieved by LY293558 administration, while the rats who received LY293558 + CRM displayed no neurodegeneration; (6) body weight loss and recovery in the LY293558 + CRM-treated rats did not differ from those in control rats who were not exposed to soman. The data show that treatment with LY293558 + CRM provides full antiseizure and neuroprotective efficacy against soman.

Susceptibility to Soman Toxicity and Efficacy of LY293558 Against Soman-Induced Seizures and Neuropathology in 10-Month-Old Male Rats.

Acute nerve agent exposure causes prolonged status epilepticus (SE), leading to death or long-term brain damage. We have previously demonstrated that LY293558, an AMPA/GluK1 kainate receptor antagonist, terminates SE induced by the nerve agent soman and protects from long-term brain damage, in immature rats and young-adult rats, even if administered with a relatively long latency from the time of exposure. However, susceptibility to the lethal consequences of SE increases with age, and mortality by SE induced by soman is substantially greater in older animals. Therefore, in the present study, we compared the susceptibility to soman toxicity of 10-month-old male rats with that of young-adult male rats (42 to 50days old) and examined the protective efficacy of LY293558 in the older group. A lower percentage of the 10-month-old rats developed SE after injection of 1.2×LD50 soman, compared to the young adults, the latency to seizure onset was longer in the older rats, and seizure intensity did not differ between the two age groups. However, mortality rate in the older rats who developed SE was higher than in the young adults. Acetylcholinesterase activity in the amygdala, hippocampus, and piriform cortex did not differ between the two age groups. Administration of LY293558 at 20 or 60min post-exposure suppressed SE, increased 24-h survival rate, decreased the long-term risk of death, reduced neuronal degeneration in the amygdala, hippocampus, piriform, and entorhinal cortices, and facilitated recovery from body weight loss. Thus, LY293558 is an effective countermeasure against soman toxicity also in older animals.

Pharmacokinetic profile and quantitation of protection against soman poisoning by the antinicotinic compound MB327 in the guinea-pig.

Current organophosphorus nerve agent medical countermeasures do not directly address the nicotinic effects of poisoning. A series of antinicotinic bispyridinium compounds has been synthesized in our laboratory and screened in vitro. Their actions can include open-channel block at the nicotinic receptor which may contribute to their efficacy. The current lead compound from these studies, MB327 1,1'-(propane-1,3-diyl)bis(4-tert-butylpyridinium) as either the diiodide (I2) or dimethanesulfonate (DMS) has been examined in vivo for efficacy against nerve agent poisoning. MB327 I2 (0-113mgkg(-1)) or the oxime HI-6 DMS (0-100mgkg(- 1)), in combination with atropine and avizafone (each at 3mgkg(-1)) was administered to guinea-pigs 1min following soman poisoning. Treatment increased the LD50 of soman in a dose-dependent manner. The increase was statistically significant (p<0.01) at the 33.9mgkg(-1) (MB327) or 30mgkg(-1) (HI-6) dose with a comparable degree of protection obtained for both compounds. Following administration of 10mgkg(-1) (i.m.), MB327 DMS reached plasma Cmax of 22μM at 12min with an elimination t1/2 of 22min. In an adverse effect study, in the absence of nerve agent poisoning, a dose of 100mgkg(-1) or higher of MB327 DMS was lethal to the guinea-pigs. A lower dose of MB327 DMS (30mgkg(-1)) caused flaccid paralysis accompanied by respiratory impairment. Respiration normalised by 30min, although the animals remained incapacitated to 4h. MB327 or related compounds may be of utility in treatment of nerve agent poisoning as a component of therapy with atropine, anticonvulsant and oxime, or alternatively as an infusion under medical supervision.

Supralethal poisoning by any of the classical nerve agents is effectively counteracted by procyclidine regimens in rats

A treatment regimen consisting of HI-6, levetiracetam, and procyclidine (termed the triple regimen) has previously been shown to work as a universal therapy against soman poisoning in rats, since it has capacities to function as both prophylactic and therapeutic measure. The purpose of the present study was to examine whether the triple regimen may have antidotal efficacy against intoxication by other classical nerve agents than soman. The treatment was given 1 and 5min after exposure to a supralethal dose of nerve agents, and the results showed that the triple regimen successfully prevented or terminated seizures and preserved the lives of rats exposed to 5×LD50 of soman, sarin, cyclosarin, or VX, but solely 3×LD50 of tabun was managed by this regimen. To meet the particular antidotal requirements of tabun, the triple regimen was reinforced with obidoxime and was made to a quadruple regimen that effectively treated rats intoxicated by 5×LD50 of tabun. The rats recovered very well and the majority gained pre-exposure body weight within 7 days. Neuropathology was seen in all groups regardless of whether the rats seized or not. The most extensive damage was produced by sarin and cyclosarin. Differentiation between the nerve agents’ potency to cause lesions was probably seen because the efficacious treatments ensured survival of supralethal poisoning. A combination of 2 oximes and 2 anticonvulsants may be a prerequisite to counteract effectively high levels of poisoning by any classical nerve agent.

Galantamine prevents long-lasting suppression of excitatory synaptic transmission in CA1 pyramidal neurons of soman-challenged guinea pigs

Galantamine, a drug currently approved for the treatment of Alzheimer's disease, has recently emerged as an effective pretreatment against the acute toxicity and delayed cognitive deficits induced by organophosphorus (OP) nerve agents, including soman. Since cognitive deficits can result from impaired glutamatergic transmission in the hippocampus, the present study was designed to test the hypothesis that hippocampal glutamatergic transmission declines following an acute exposure to soman and that this effect can be prevented by galantamine. To test this hypothesis, spontaneous excitatory postsynaptic currents (EPSCs) were recorded from CA1 pyramidal neurons in hippocampal slices obtained at 1h, 24h, or 6–9 days after guinea pigs were injected with: (i) 1×LD50 soman (26.3μg/kg, s.c.); (ii) galantamine (8mg/kg, i.m.) followed 30min later by 1×LD50 soman, (iii) galantamine (8mg/kg, i.m.), or (iv) saline (0.5ml/kg, i.m.). In soman-injected guinea pigs that were not pretreated with galantamine, the frequency of EPSCs was significantly lower than that recorded from saline-injected animals. There was no correlation between the severity of soman-induced acute toxicity and the magnitude of soman-induced reduction of EPSC frequency. Pretreatment with galantamine prevented the reduction of EPSC frequency observed at 6–9 days after the soman challenge. Prevention of soman-induced long-lasting reduction of hippocampal glutamatergic synaptic transmission may be an important determinant of the ability of galantamine to counter cognitive deficits that develop long after an acute exposure to the nerve agent.

Effect of polyethylene glycol conjugation on the circulatory stability of plasma-derived human butyrylcholinesterase in mice

Exogenously administered human serum butyrylcholinesterase (Hu BChE) was demonstrated to function as a bioscavenger of highly toxic organophosphorus (OP) compounds in several animal species. Since the enzyme is isolated from human serum, it is currently the most suitable pretreatment for human use. A dose of 200–300mg/70kg human adult is projected to provide protection from 2 X LD50 of soman. Due to the limited supply of Hu BChE, strategies aimed at reducing the dose of enzyme are being explored. In this study, we investigated the effect of modification with polyethylene glycol (PEG) on the in vivo stability of Hu BChE. Mice were given two injections of either Hu BChE or Hu BChE modified with PEG-5K or PEG-20K, six weeks apart. Pharmacokinetic parameters, such as mean residence time (MRT), maximal concentration (Cmax), elimination half-life (T1/2), and area under the plasma concentration time curve extrapolated to infinity (AUC), were determined. For the first injection, values for MRT, T1/2, Cmax, and AUC for PEG-5K-Hu BChE and PEG-20K-Hu BChE were similar to those for Hu BChE. These values for the second injection of Hu BChE as well as PEG-Hu BChEs were lower as compared to those for the first injections, likely due to antibody-mediated clearance.

A combination of [+] and [−]-Huperzine A improves protection against soman toxicity compared to [+]-Huperzine A in guinea pigs

The neuropathologic mechanisms after exposure to lethal doses of nerve agent are complex and involve multiple biochemical pathways. Effective treatment requires drugs that can simultaneously protect by reversible binding to the acetylcholinesterase (AChE) and blocking cascades of seizure related brain damage, inflammation, neuronal degeneration as well as promoting induction of neuroregeneration. [−]-Huperzine A ([−]-Hup A), is a naturally occurring potent reversible AChE inhibitor that penetrates the blood–brain barrier. It also has several neuroprotective effects including modification of beta-amyloid peptide, reduction of oxidative stress, anti-inflammatory, anti-apoptotic and induction and regulation of nerve growth factor. Toxicities at higher doses restrict the neuroporotective ability of [−]-Hup A for treatment. The synthetic stereoisomer, [+]-Hup A, is less toxic due to poor AChE inhibition and is suitable for both pre-/post-exposure treatments of nerve agent toxicity. [+]-Hup A block the N-methyl-d-aspartate (NMDA)-induced seizure in rats, reduce excitatory amino acid induced neurotoxicity and also prevent soman induced toxicity with minimum performance decrement. Unique combinations of two stereo-isomers of Hup A may provide an excellent pre/post-treatment drug for the nerve agent induced seizure/status epilepticus. We investigated a combination of [+]-Hup A with a small dose of [−]-Hup A ([+] and [−]-Hup A) against soman toxicity. Our data showed that pretreatment with a combination [+] and [−]-Hup A significantly increased the survival rate and reduced behavioral abnormalities after exposure to 1.2×LD50 soman compared to [+]-Hup A in guinea pigs. In addition, [+] and [−]-Hup A pretreatment inhibited the development of high power of EEG better than [+]-Hup A pretreatment alone. These data suggest that a combination of [+] and [−]-Hup A offers better protection than [+]-Hup A and serves as a potent medical countermeasure against lethal dose nerve agent toxicity in guinea pigs.

Amino acid residues at the N- and C-termini are essential for the folding of active human butyrylcholinesterase polypeptide

Human serum butyrylcholinesterase (HuBChE) is currently the most suitable bioscavenger for the prophylaxis of highly toxic organophosphate (OP) nerve agents. A dose of 200mg of HuBChE is envisioned as a prophylactic treatment that can protect humans from an exposure of up to 2×LD50 of soman. The limited availability and administration of multiple doses of this stoichiometric bioscavenger make this pretreatment difficult. Thus, the goal of this study was to produce a smaller enzymatically active HuBChE polypeptide (HBP) that could bind to nerve agents with high affinity thereby reducing the dose of enzyme. Studies have indicated that the three-dimensional structure and the domains of HuBChE (acyl pocket, lip of the active center gorge, and the anionic substrate-binding domain) that are critical for the binding of substrate are also essential for the selectivity and binding of inhibitors including OPs. Therefore, we designed three HBPs by deleting some N- and C-terminal residues of HuBChE by maintaining the folds of the active site core that includes the three active site residues (S198, E325, and H438). HBP-4 that lacks 45 residues from C-terminus but known to have BChE activity was used as a control. The cDNAs for the HBPs containing signal sequences were synthesized, cloned into different mammalian expression vectors, and recombinant polypeptides were transiently expressed in different cell lines. No BChE activity was detected in the culture media of cells transfected with any of the newly designed HBPs, and the inactive polypeptides remained inside the cells. Only enzymatically active HBP-4 was secreted into the culture medium. These results suggest that residues at the N- and C-termini are required for the folding and/or maintenance of HBP into an active stable, conformation.

Combined diazepam and HDAC inhibitor treatment protects against seizures and neuronal damage caused by soman exposure

The occurrence of status epilepticus (SE) is considered the main cause of brain lesions and morphological alterations, such as hippocampal neuron loss, that result in chronic epilepsy. Previous work demonstrated the convulsive and widespread neuropathological effects of soman, an organophosphorus compound that causes SE and severe recurrent seizures as a result of exposure. Seizures begin rapidly after exposure, can continue for hours, and contribute to prolonged physical incapacitation of the victim. This study attempts to identify anticonvulsive and neuroprotective drugs against soman exposure. Male Sprague-Dawley rats were exposed to 1.0LD50 soman. EEGraphical and neuropathological (Fluoro-Jade B staining) effects were analyzed at 72h post-exposure to soman and subsequent treatments with diazepam (DZP) alone or in combination with histone deacetylase inhibitors, suberoylanilide hydroxamic acid (SAHA) or valproic acid (VPA). The extent of brain damage was dependent on the length of SE and not on the number of recurrent seizures. DZP treatment alone decreased SE time and damage in hippocampus, amygdala, thalamus and cortex, but not in piriform nuclei. The combination of DZP and VPA 100mg/kg showed more anticonvulsive effects, decreased SE time, and afforded more neuroprotection in the hippocampus, mainly the ventral portion. The combination DZP and SAHA 25mg/kg was more neuroprotective, but not more anticonvulsant than DZP alone. The DZP combination with VPA HDAC inhibitor proved to be a good treatment for SE and neuronal damage caused by soman exposure.

Neuroprotective effects of imidazenil against chemical warfare nerve agent soman toxicity in guinea pigs

The chemical warfare nerve agent, soman irreversibly inhibits acetylcholinesterase (AChE) leading to hypercholinergy and seizures which trigger glutamate toxicity and status epilepticus ultimately resulting in neuropathology and neurobehavioral deficits. The standard emergency treatment comprising of anticholinergic, AChE reactivator and anticonvulsant does not completely protect against soman toxicity. We have evaluated imidazenil, a new anticonvulsant imidazo benzodiazepine with high affinity and intrinsic efficacy at α5-, α2-, and α3- but low intrinsic efficacy at α1-containing GABAA receptors and is devoid of cardiorespiratory depression, sedative/hypnoitc and amnestic actions and does not elicit tolerance and dependence liabilities unlike diazepam, for protection against soman toxicity. Guinea pigs implanted with bipotential radiotelemetry probes for recording EEG and ECG were administered with 26μg/kg pyridostigmine bromide 30min prior to 2× LD50 soman exposure and 1min later treated with a combination of 2mg/kg atropine sulfate and 25mg/kg 2-pralidoxime and various doses of imidazenil. Intramuscular administration of imidazenil, dose-dependently protected against 2× LD50 of soman toxicity up to 1mg/kg. Further increase in the dose of imidazenil to 2.5mg/kg was less effective than 1mg/kg probably due to non-specific actions at sites other than GABAA receptors. Compared to vehicle group, 1mg/kg imidazenil treatment showed optimal increase in survival rate, reduction in behavioral manifestations and high power of EEG spectrum as well as neuronal necrosis. These data suggest that imidazenil is an effective anticonvulsant for medical countermeasure against soman-induced toxicity.

Diet composition modifies the toxicity of repeated soman exposure in rats

It was previously demonstrated that diet potently modulates the toxic effects of an acute lethal dose of the nerve agent soman. The current investigation was undertaken to examine the influence of diet on the cumulative toxicity of repeated soman administration. Rats were fed one of four distinct diets (standard, choline-enriched, glucose-enriched, or ketogenic) for four weeks prior to and throughout a repeated soman dosing and recovery regimen. Each diet group included animals exposed to an equivalent volume of saline that served as negative controls. In exposure Week 1, animals received three consecutive daily doses of 0.4LD50 soman. In exposure Week 2, animals received four consecutive daily doses of 0.5LD50 soman. In exposure Week 3, animals received five consecutive daily doses of 0.5LD50 soman. Week 4 constituted a post-exposure recovery evaluation. Throughout the experiment, behavioral function was assessed by a discriminated avoidance test that required intact sensory and motor function. Survival and body weight changes were recorded daily. Differences in toxicity as a function of diet composition became apparent during the first week. Specifically, rats fed the glucose-enriched diet showed pronounced intoxication during Week 1, resulting in imperfect survival, weight loss, and deteriorated avoidance performance relative to all other groups. All rats fed the glucose-enriched diet died by the end of exposure Week 2. In contrast, only 10% of animals fed the standard diet died by the end of Week 2. Also in Week 2, weight loss and disrupted avoidance performance were apparent for all groups except for those fed the ketogenic diet. This differential effect of diet composition became even more striking in Week 3 when survival in the standard and choline diet groups approximated 50%, whereas survival equaled 90% in the ketogenic diet group. Avoidance performance and weight loss measures corroborated the differential toxicity observed across diet groups. Upon cessation of soman exposure during the final week, recovery of weight and avoidance performance in survivors was comparable across diet groups. These results systematically replicate previous findings demonstrating that diet composition exacerbates or attenuates toxicity in rodents exposed acutely to organophosphorus compounds.

Prophylactic and therapeutic efficacy of the soman-simulator, pinacolyl dimethylphosphinate

Atropinized rats, intoxicated with 6 or 8 X LD50 soman and subsequently treated with the oxime HI-6 died several hours after intoxication. Oral or intravenous administration of the soman-simulator, pinacolyl dimethylphosphinate (PDP), given at progressively increasing time intervals before soman, appeared to be very active in preventing death and secondary failure of neuromuscular transmission that followed HI-6-induced recovery. Therapeutically, PDP was only effective when given immediately after soman intoxication and oxime treatment. In animals that received no treatment otherwise, intravenous administration of PDP 10 min before intoxication with 1 X LD50 soman did not enhance lethality.

Influence of pinacolyl dimethylphosphinate on soman storage in rats.

Atropinized rats pretreated with pinacolyl dimethylphosphinate (PDP) or saline were intoxicated with 6 X LD50 soman and, after 30 and 60 min, the absolute amounts of soman in diaphragms and lungs were measured gas chromatographically. The absolute amounts of free soman in both types of tissues were similar and were decreased after 60 min intoxication compared with the 30 min intoxication period. Pretreatment of rats with PDP reduced the amount of soman in the tissues by 63-78%. Incubation of isolated diaphragms and lungs with sodium fluoride (2.5 mM) increased the amount of free soman in these tissues by 2.6 X 10(3) and 16 X 10(3)%, respectively. An assay to study the binding of tritiated PDP was developed. Although this assay was suitable to study the binding of tritiated quinuclidinyl benzilate to rat brain, no binding between tritiated PDP and diaphragm or brain tissue could be detected. It was concluded that PDP may counteract soman storage by another mechanism than occupation of binding sites.

The protection of primates against soman poisoning by pretreatment with pyridostigmine.

The effectiveness of pyridostigmine pretreatment against soman poisoning has been determined in rhesus monkeys and marmosets receiving atropine therapy. Pretreatment with the maximum sign-free dose (200 microgram kg-1, i.v.) raised the subcutaneous LD50 of soman by a factor of 28 in rhesus monkeys and 15 in marmosets. The protection afforded by a quarter of the sign-free dose of pyridostigmine was not significantly less. These levels of protection are higher than any reported in non-primate species.

Long-term effects of cytokine treatment on cognitive behavioral recovery and neuronal regeneration in soman-poisoned mice

Increasing numbers of reports have substantiated to date, a beneficial influence of cytokine treatment on neurogenesis processes in damaged rodent brains. Most of these investigations further revealed that cytokine treatment induces either partial or full recovery of cognitive behavior impaired by cerebral lesions. Hence, we investigated the effects of a cytokine treatment on neuronal regeneration and cognitive behavior in mice subjected to nerve agent exposure. Subcutaneous injection of a mixture of 40 μg/kg fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF) was administered daily over 8 days to soman-poisoned mice (1.2 LD50 soman). Memory performances (T-maze and Morris water maze) and emotional behavior (elevated plus maze; auditory and contextual response in a fear conditioning task) were assessed on post-soman days 30 and 90. Brains were collected on post-soman days 9, 30 and 90 so as to perform NeuN-immunohistochemistry in the hippocampus and amygdala (neuronal regeneration quantification). Following soman-induced brain lesions, a spontaneous neuronal regeneration occurred in both the hippocampus and amygdala. Cytokine treatment enhanced neuronal regeneration in the hippocampus however not in the amygdala. Soman poisoning fostered altogether memory impairments as well as anxiety or fear-like behavioral disturbances in mice. A spontaneous recovery of standard emotional behavior occurred overtime. Such a recovery displayed significantly enhanced speed under cytokine treatment. Unfortunately, no memory performance recovery was evidenced in soman-intoxicated mice whether treated or not with cytokines.

Antidotal effect of combinations obidoxime/HI-6 and memantine in mice poisoned with soman, dichlorvos or heptenophos

In acute organophosphate poisoning the issue of special concern is the appearance of muscle fasciculations and convulsions that cannot be adequately antagonised by the use of atropine and oxime therapy. The aim of this study was to examine atidotal effect of obidoxime or HI-6 combinations with memantine in mice poisoned with soman, dichlorvos or heptenophos. Male Albino mice were pretreated intravenously (iv) with increasing doses of oximes and/or memantine (10 mg/kg) at various times before poisoning with 1.3 LD-50 of soman, dichlorvos or heptenophos, in order to determine the median effective dose and the efficacy half-time. In a separate experiment, cerebral extravasation of Evans blue dye (40 mg/kg iv) was examined after application of memantine (10 mg/kg iv), midazolam (2.5 mg/kg intraperitonealy--ip) and ketamine (20 mg/kg ip) 5 minutes before soman (1 LD-50 subcutaneously--sc). Coadministration of memantine induced a significant decrease in median effective dose in null time of both HI-6 (7.96 vs 1.79 gmoL/kg in soman poisoning) and obidoxime (16.80 vs 2.75 micromoL/kg in dichlorvos poisoning; 21.56 vs 6.63 micromoL/kg in heptenophos poisoning). Memantine and midazolam succeded to counteract the soman-induced proconvulsive activity. Memantine potentiated the antidotal effect of HI-6 against a lethal dose of soman, as well as the ability of obidoxime to antagonize the toxic effects of dichlorvos and heptenophos probably partly due to its anticonvulsive properties.

Molecular and Cellular Actions of Galantamine: Clinical Implications for Treatment of Organophosphorus Poisoning

There have been continued efforts to develop effective antidotal therapies against poisoning with organophosphorus (OP) compounds, including nerve agents and pesticides. We reported recently that galantamine, a drug used to treat Alzheimer's disease, administered before (up to 3 h) or soon after (up to 5 min) an exposure of guinea pigs to 1.5-2 x LD50 soman or sarin effectively counteracted the acute toxicity and lethality of the nerve agents provided that the animals were also post-treated with atropine. Here, we demonstrate that administered to guinea pigs at 30 min before or up to 15 min after an acute challenge with 1 x LD50 soman, galantamine (8 mg/kg, intramuscular) alone is sufficient to counteract the lethality and acute toxicity of the nerve agent. Evidence is also provided that 100% survival can be attained when the association of appropriate doses of galantamine and atropine is administered 30-45 min after the challenge of the guinea pigs with 1 x LD50 soman. Galantamine counteracts the neurodegeneration and the changes in the nicotinic cholinergic system that result from an acute exposure of guinea pigs to 1 x LD50 soman. The results presented herein corroborate that galantamine is an effective antidote against OP poisoning.