Some Possibilities to Study New Prophylactics against Nerve Agents.

Nerve agents belong to the most dangerous chemical warfare agents and can be/were misused by terrorists. Effective prophylaxis and treatment is necessary to diminish their effect. General principles of prophylaxis are summarized (protection against acetylcholinesterase inhibition, detoxification, treatment "in advance" and use of different drugs). They are based on the knowledge of mechanism of action of nerve agents. Among different examinations, it is necessary to test prophylactic effectivity in vivo and compare the results with protection in vitro. Chemical and biological approaches to the development of new prophylactics would be applied simultaneously during this research. Though the number of possible prophylactics is relatively high, the only four drugs were introduced into military medical practice. At present, pyridostigmine seems to be common prophylactic antidote; prophylactics panpal (tablets with pyridostigmine, trihexyphenidyl and benactyzine), transant (transdermal patch containing HI-6) are other means introduced into different armies as prophylactics. Scavenger commercionally available is Protexia®. Future development will be focused on scavengers, and on other drugs either reversible cholinesterase inhibitors (e.g., huperzine A, gallantamine, physostigmine, acridine derivatives) or other compounds.

Two possibilities how to increase the efficacy of antidotal treatment of nerve agent poisonings.

Highly toxic organophosphorus inhibitors of acetylcholinesterase referred as nerve agents are considered to be among the most dangerous chemical warfare agents. The oximes represent very important part of medical countermeasures of nerve agent poisonings. They are used to reactivate the nerve agent-inhibited acetylcholinesterase. Despite long-term research activities, there is no single, broad-spectrum oxime suitable for the antidotal treatment of poisoning with all organophosphorus agents. There are two approaches how to increase and broaden the effectiveness of antidotal treatment of poisoning with nerve agents - to develop new structural analogues of currently available oximes and/or to combine currently available or newly developed oximes. The review describes the evaluation of the potency of newly developed oximes (especially the oxime K203) or combinations of oximes to reactivate nerve agent-inhibited acetylcholinesterase and to counteract the acute toxicity of nerve agents in comparison with single commonly used oxime (obidoxime, trimedoxime or HI-6).

Biochemical insight into soman intoxication and treatment with atropine, HI-6, trimedoxime, and K203 in a rat model.

OBJECTIVE: The present experiment is based on biochemical assessment of nerve agent soman intoxication and atropine, respectively atropine and HI-6, trimedoxime or K203 treatment in rats. BACKGROUND: Nerve agents are toxic substances irreversibly inhibiting enzyme acetylcholinesterase (AChE). Treatment is typically based on application of atropine and oxime reactivator. Atropine is able to protect overstimulation of muscarinic acetylcholine receptors. Application of oxime reactivator enable return of AChE activity and full suppression of intoxication. METHODS: In a total, fifteen biochemical markers were assayed in plasma or blood of intoxicated animals. 42 rats were divided into 7 groups each 6 individuals. The first group was exposed to atropine; the second group was exposed to one LD50 of soman and atropine. The groups 3-5 were exposed in a same way as the second group and were treated with oxime reactivators: HI-6 (group 3), trimedoxime (4) and K203 (5). The sixth group was control treated with saline solution only. The last (seventh) group was intoxicated with soman only. RESULTS: The most striking shifts were found for blood acetylcholinesterase and plasma creatinine, glucose, inorganic phosphate as well as uric acid. Lactate dehydrogenase and aspartate aminotransferase assays were useless due to soman interference. CONCLUSION: It was demonstrated that treatment was able to protect poisoned animals from metabolic disorder represented by hyperglycemia and nephropathy represented by hyperuricemia and elevated creatinine. Soman exposure and treatment with the oxime reactivators and/or atropine contains quite complex and still not well understood side mechanisms (Tab. 2, Fig. 1, Ref. 25).

Potency of several oximes to reactivate human acetylcholinesterase and butyrylcholinesterase inhibited by paraoxon in vitro.

Organophosphorus pesticides (e.g. chlorpyrifos, malathion, and parathion) and nerve agents (sarin, tabun, and VX) are highly toxic organophosphorus compounds with strong inhibition potency against two key enzymes in the human body-acetylcholinesterase (AChE; EC 3.1.1.7) and butyrylcholinesterase (BuChE; EC 3.1.1.8). Subsequent accumulation of acetylcholine at synaptic clefts can result in cholinergic crisis and possible death of intoxicated organism. For the recovery of inhibited AChE, derivatives from the group of pyridinium or bispyridinium aldoximes (called oximes) are used. Their efficacy depends on their chemical structure and also type of organophosphorus inhibitor. In this study, we have tested potency of selected cholinesterase reactivators (pralidoxime, obidoxime, trimedoxime, methoxime and H-oxime HI-6) to reactivate human erythrocyte AChE and human plasma BuChE inhibited by pesticide paraoxon. For this purpose, modified Ellman's method was used and two different concentrations of oximes (10 and 100 microM), attainable in the plasma within antidotal treatment of pesticide intoxication were tested. Results demonstrated that obidoxime (96.8%) and trimedoxime (86%) only reached sufficient reactivation efficacy in case of paraoxon-inhibited AChE. Other oximes evaluated did not surpassed more than 25% of reactivation. In the case of BuChE reactivation, none of tested oximes surpassed 12.5% of reactivation. The highest reactivation efficacy was achieved for trimedoxime (12.4%) at the concentration 100 microM. From the data obtained, it is clear that only two from currently available oximes (obidoxime and trimedoxime) are good reactivators of paraoxon-inhibited AChE. In the case of BuChE, none of these reactivators could be used for its reactivation.

Activation of mitogen activated protein kinase (MAPK) pathways after soman poisoning in rat cerebellar granule neurons.

The expression of activated p38 mitogen-activated protein kinase (MAPK) and activated MAPK transcription factors c-jun, c-myc and elk-1 were examined in rat cerebellum after soman poisoning to determine the pathogenetic mechanism of the non-specific long-term effects of nerve agents. Male Wistar rats were poisoned by intramuscular administration of soman at a dose 60 microg kg(-1) (70% LD(50)) and samples were taken 1, 7 and 14 days after poisoning, immunohistochemically stained and p-p38MAPK, p-c-jun, p-c-myc and p-elk-1 expressions were measured using image analysis. Control groups were administered with saline instead of soman. The expression of activated p38MAPK and c-myc increased 14 days after soman poisoning while c-jun and elk-1 expressions remained unchanged 1, 7 and 14 days after soman poisoning. Delayed activation of p38 MAPK and its targets might be involved in the pathogenetic mechanism of the long-term neurophysiological toxic effects of nerve agents.

Five oximes (K-27, K-48, obidoxime, HI-6 and trimedoxime) in comparison with pralidoxime: survival in rats exposed to methyl-paraoxon.

There is a clear need for broad-spectrum cholinesterase reactivators (active against a multitude of organophosphorus ester enzyme inhibitors) with a higher efficacy than pralidoxime. The purpose of the study was to quantify in vivo the extent of oxime-conferred protection, using methyl-paraoxon [dimethyl p-nitrophenyl phosphate; (methyl-POX)] as a cholinesterase inhibitor. There were seven groups of six rats in each cycle of the experiment. Group 1 (G1) received 2 micromol methyl-POX ( approximately LD(50)), the other groups (G2-7) received 2 micromol methyl-POX + one of the six reactivators. The animals were monitored for 48 h and the time of mortality was recorded. The procedure was repeated six times. All substances were applied i.p. The experiments were repeated using 3 and 5 micromol methyl-POX. Mortality data were compared and hazards ratios (relative risks) ranked using the Cox proportional hazards model with methyl-POX dose and group (reactivator) as time-independent covariables. The relative risk of death estimated by Cox analysis (95% CI) in oxime-treated animals when compared with untreated animals, adjusted for methyl-POX dose (high/low) was K-27, 0.58 (0.42-0.80); K-48, 0.60 (0.43-0.83); trimedoxime, 0.76 (0.55-1.04); pralidoxime, 0.88 (0.65-1.20); obidoxime, 0.93 (0.68-1.26); HI-6, 0.96 (0.71-1.31). Only K-27 and K-48 provided statistically significant protection in rats exposed to methyl-POX. Despite the lower inhibitory potency (higher IC(50)) of methyl-POX compared with POX (ratio 4:1), the ability of oxime reactivators to protect from methyl-POX induced mortality was reduced compared with protection from POX (ethyl-analog).

In vitro oxime reactivation of red blood cell acetylcholinesterase inhibited by methyl-paraoxon.

Oximes are cholinesterase reactivators of use in poisoning with organophosphorus ester enzyme inhibitors. Pralidoxime (PRX) is the oxime used in the United States. Clinical experience with pralidoxime (and other oximes) is disappointing and the routine use has been questioned. Furthermore oximes are not equally effective against all existent enzyme inhibitors. There is a clear demand for 'broad spectrum' cholinesterase reactivators with a higher efficacy than those clinically available. To meet this need over the years new reactivators of cholinesterase of potential clinical utility have been developed. The purpose of the study was to quantify 'in vitro' the extent of protection conferred by available (pralidoxime and methoxime) and experimental (K-27, K-33 and K-48) oximes, using methyl-paraoxon (methyl-POX) as an esterase inhibitor and to compare the results with those previously obtained using paraoxon (POX) as an inhibitor. Red blood cell (RBC) acetylcholinesterase (AChE) activities in whole blood were measured photometrically in the presence of different methyl-POX concentrations and IC(50) values calculated. Determinations were repeated in the presence of increasing oxime concentrations. The IC(50) of methyl-POX (59 nm) increased with the oxime concentration in a linear manner. The calculated IC(50) values were plotted against the oxime concentrations to obtain an IC(50) shift curve. The slope of the shift curve (tg alpha) was used to quantify the magnitude of the protective effect (nm IC(50) increase per microm reactivator). Based on our determinations the new K-series of reactivators is superior to pralidoxime (tg alpha = 1.9) and methoxime (tg alpha = 0.7), K-27 and K-48 being the outstanding compounds with a tg alpha value of 10 (nm IC(50) increase per microm reactivator), which is approximately five times the reactivator ability of PRX. The tg alpha value determined for K-33 was 6.3. The ranking of reactivator potencies of the examined oximes determined with methyl-POX as an inhibitor (K-27 = K-48 > K-33 > pralidoxime > methoxime) is similar to the ranking previously reported by us using POX as an inhibitor (K-27 > or = K-48 > K-33 > methoxime = pralidoxime). There is an (expected) inverse relationship between the binding constant K and the slope of the IC(50) shift curve (tg alpha) for all oximes examined. K-27 and K-48 (the most protective substances judging by the tg alpha) having the lowest K value (highest affinity). In vivo testing of the new oximes as methyl-paraoxon protective agents is necessary.

Inhibition of blood cholinesterases following intoxication with VX and its derivatives.

Nerve agents can be divided into G-agents (sarin, soman, tabun, cyclosarin etc.) and V-agents. The studies dealing with V-agents (O-alkyl S-2-dialkylaminoethyl methyl phosphonothiolates) are limited to one or two representatives only (VX, Russian VX). Anticholinesterase properties of 11 V-agents were studied in rats in vivo. Following intoxication with these agents in doses of 1 x LD(50) (intramuscular administration), activities of cholinesterases in the blood were continuously monitored and half-lives (t(0.5)) of inhibition were determined. These values varied from 3 min (VX and some other agents) to 10-14 min (derivatives substituted on the phosphorus head by O-ethyl- or O-isopropyl-, and by dimethyl-, diethyl- and dibutyl- on the nitrogen). Acetylcholinesterase activities in selected parts of the brain and diaphragm (30 min after the intoxication) were also detected. A correlation between toxicities and rates of inhibition of the blood enzymes was demonstrated. A similar relationship between acetylcholinesterase inhibition in vitro (from literature data) and half-lives of the blood cholinesterases was also observed. Though the chemical similarity of V compounds is evident, marked differences were observed among different derivatives; however, all agents examined had high inhibition potency corresponding to their toxicities.

New K-Oximes (K-27 and K-48) in Comparison with Obidoxime (LuH-6), HI-6, Trimedoxime (TMB-4), and Pralidoxime (2-PAM): Survival in Rats Exposed IP to the Organophosphate Paraoxon.

ABSTRACT Oximes are cholinesterase reactivators used in organophosphorus compound poisoning. The purpose of the study was to compare the protective effect of the K-oximes (K-27 and K-48) in male rats with that of obidoxime (LuH-6), trimedoxime (TMB-4), and HI-6, using paraoxon (POX) as a cholinesterase inhibitor. Pralidoxime (2-PAM) was also retested. Seven groups of six rats each were used. Group 1 (G(1)) received 1 mumol/rat POX ( approximately LD(75)), the other groups (G(2-7)) received 1 mumol/rat POX + one of the six reactivators. The animals were monitored for 48 h and time of mortality was recorded. The procedure was repeated seven times. Subsequently, experiments as described were repeated using 10 and 15 mumol/rat POX. Mortality data were compared and hazards ratios (relative risks) ranked with the Cox proportional hazards model using the POX dose and group (reactivator) as time-independent covariables. K-27 followed by K-48 were the most potent reactivators. K-27 was statistically significantly superior to all other reactivators except K-48. The relative risk of death estimated by Cox analysis in K-27- and K-48-treated animals when compared with untreated animals, adjusted for the POX dose, was 0.22 (95% confidence interval [CI], 0.15 to 0.31) and 0.26 (95% CI, 0.18 to 0.37), respectively. We concluded that in the animal model used K-27 and K-48 are superior to older oximes in their ability to protect from paraoxon effects. They should be tested further using methyl- and propyl-organophosphates as toxic agents.

Five oximes (K-27, K-33, K-48, BI-6 and methoxime) in comparison with pralidoxime: survival in rats exposed to the organophosphate paraoxon.

Oximes are cholinesterase reactivators used in organophosphorus poisoning. Clinical experience with pralidoxime (PRX) and other oximes is disappointing and their routine use has been questioned. In addition it is known that not all oximes are equally effective against all existing organophosphorus compounds. There is a demand for broad-spectrum reactivators with a higher efficacy than PRX. Based on our previous in vitro work the protection conferred by the various new oximes against inhibition by paraoxon as quantified by the IC(50) shift (nM increase in the IC(50) of the inhibitor per microM oxime present) is: 0.3 (PRX), 0.4 (methoxime; MMC-4), 1 (K-33), 1.2 (BI-6), 1.5 (K-48) and 3.7 (K-27). The purpose of the study was to quantify in vivo the extent of oxime-conferred protection, using paraoxon (POX) as a cholinesterase inhibitor and to test whether in vitro efficacy translates to protection from mortality. There were seven groups of six rats in each cycle of the experiment. Group 1 (G1) received 1 micromol POX (approximately LD(75)), the other groups (G2-G7) received 1 micromol POX + of one the six reactivators. The animals were monitored for 48 h and the time of mortality was recorded. The procedure was repeated five times (cycles). All substances were applied i.p. The experiments were repeated using 2, 3, 5 and 10 micromol POX. Mortality data were compared and hazards ratios (relative risks) ranked using the Cox proportional hazards model using POX dose and group (reactivator) as time-independent covariables. The relative risk of death estimated by Cox analysis (95% CI) in oxime treated animals when compared with untreated animals, adjusted for POX dose (high/low) was K-27: 0.26 (0.19-0.35); K-48: 0.34 (0.25-0.45); methoxime: 0.38 (0.29-0.50); BI-6: 0.53 (0.41-0.69); PRX: 0.70 (0.54-0.91); K-33: 0.82 (0.63-1.07). It is concluded that K-27 and K-48 are the most promising new oximes. The compounds with the best results in vitro also confer the best protection in vivo. Further testing using methyl- and propyl-organophosphates are needed.

The influence of antidotal treatment of low-level tabun exposure on cognitive functions in rats using a water maze.

In this study, the influence of antidotal treatment of tabun poisoning on cognitive function, in the case of low-level tabun exposure, was studied. The impairment of cognitive function was evaluated by the measurement of spatial learning and memory in rats poisoned with a sublethal dose of tabun and treated with atropine alone or in combination with newly developed oximes {K027 [1-(4-hydroxyiminomethyl- pyridinium)-3-(4-carbamoylpyridinium) propane dibromide] and K048 [1-(4-hydroxyimino- methylpyridinium)-3-(4-carbamoylpyridinium) butane dibromide]} or currently available oxime (trimedoxime), using the Morris water maze. While atropine alone caused an impairment of studied cognitive functions, the addition of an oxime to atropine contributes to the improvement of cognitive performance of treated tabun-poisoned rats regardless of the type of oxime. The differences in the ameliorative effects of oximes on atropine-induced mnemonic deficits were not significant. Therefore, each low-level nerve agent exposure should be treated by complex antidotal treatment consisting of anticholinergic drug and oxime.

Five oximes (K-27, K-33, K-48, BI-6 and methoxime) in comparison with pralidoxime: in vitro reactivation of red blood cell acetylcholinesterase inhibited by paraoxon.

Oximes are cholinesterase reactivators of use in poisoning with organophosphorus compounds. Pralidoxime (PRX) is used clinically as an adjunct to atropine in such exposure. Clinical experience with PRX (and other oximes) is, however, disappointing and routine use has been questioned. In addition it is known that oximes are not equally effective against all existing organophosphorus compounds. There is a clear demand for 'broad spectrum' cholinesterase reactivators with a higher efficacy than PRX. Over the years new reactivators of cholinesterase of potential clinical utility have been developed. Their chemical structures were derived from those of existing esterase reactivators, especially pralidoxime, obidoxime and HI-6. The purpose of the study was to quantify in vitro the extent of oxime (pralidoxime, K-27, K-33, K-48, methoxime and BI-6) conferred protection, using paraoxon as an inhibitor. Paraoxon (POX), the active metabolite of parathion (O,O-diethyl-O-p-nitro-phenyl phosphorothioate) is a non-neuropathic organophosphate. Red blood cell (RBC) acetylcholinesterase (AChE) activities in whole blood were measured photometrically in the presence of different POX concentrations and the IC50 was calculated. Determinations were repeated in the presence of increasing oxime concentrations. The IC50 of POX increases with the oxime concentration in a linear manner. The calculated IC50 values were plotted against the oxime concentrations to obtain an IC50 shift curve. The slope of the shift curve (tg alpha) was used to quantify the magnitude of the protective effect (nm IC50 increase per microm reactivator). Based on our determinations the new K series of reactivators is far superior to pralidoxime, methoxime and BI-6, K-27 being the outstanding compound with a tg alpha value of 3.7 (nm IC50 increase per microm reactivator) which is approximately 13 times the reactivator ability of PRX. In general there is an (expected) inverse relationship between the binding constant K and the slope of the IC50 shift curve (tg alpha) for all oximes examined. K-27 (the most protective substance judging by the tg alpha) has the lowest K value (highest affinity). In vivo testing of the new oximes as an organophosphate protective agent is necessary.

In vitro reactivation of sarin-inhibited brain acetylcholinesterase from different species by various oximes.

In vitro as well as in vivo evaluation of the reactivating efficacy of various oximes against nerve agent-inhibited acetylcholinesterase has been usually done with the help of animal experiments. Nevertheless, previously published data indicate that the reactivation potency of oximes may be different in human and animal species, which may hamper the extrapolation of animal data to human data. Therefore, to better evaluate the efficacy of various oximes (pralidoxime, obidoxime, HI-6, K033) to reactivate brain acetylcholinesterase inhibited by sarin by in vitro methods, human, rat and pig brain acetylcholinesterase were used to calculate kinetic parameters for the reactivation. Our results show differences among the species, depending on the type of oxime, and indicate that data from animal experiments needs to be carefully evaluated before extrapolation to humans.

A comparison of the efficacy of a bispyridinium oxime--1,4-bis-(2-hydroxyiminomethylpyridinium) butane dibromide and currently used oximes to reactivate sarin, tabun or cyclosarin-inhibited acetylcholinesterase by in vitro methods.

The efficacy of a bispyridinium oxime 1,4-bis(2-hydroxyiminomethylpyridinium) butane dibromide, called K033, and of currently used oximes (pralidoxime, obidoxime, oxime HI-6), to reactivate acetylcholinesterase inhibited by various nerve agents (sarin, tabun cyclosarin) was tested by in vitro methods. The new oxime K033 was found to be a more efficacious reactivator of sarin or cyclosarin-inhibited acetylcholinesterase than pralidoxime and obidoxime but it did not reach the efficacy of oxime HI-6 in the case of the inhibition of acetylcholinesterase by sarin or cyclosarin. On the other hand, oxime K033 was more efficacious than oxime HI-6 in reactivating tabun-inhibited acetylcholinesterase. Thus, oxime K033 seems to be a relatively efficacious broad spectrum acetylcholinesterase reactivator and, therefore, could be useful if no information about the type of nerve agent used was available.

Specification of the structure of oximes able to reactivate tabun-inhibited acetylcholinesterase.

The efficacy of various oximes to reactivate acetylcholinesterase phosphorylated by tabun (O-ethyl-N,N-dimethyl phosphoramidocyanidate) was tested by in vitro and in vivo methods. The oximes commonly used for the treatment of acute poisonings with highly toxic organophosphates appeared to be almost ineffective (HI-6, pralidoxime, methoxime) or just slightly effective (obidoxime) against tabun. On the other hand, trimedoxime seemed to be a significantly more efficacious reactivator than the others in the case of tabun poisonings. In vitro, the concentration of trimedoxime corresponding to 1.0 mmol/l was able to reach 50% reactivation of tabun-inhibited brain acetylcholinesterase. Higher reactivating potency of trimedoxime in comparison with the other commonly used oximes was demonstrated by in vivo method, too. In addition, other structural analogues of trimedoxime were found to be efficacious in counteracting tabun-induced acetylcholinesterase inhibition although not as efficacious as trimedoxime itself. Some effective acetylcholinesterase reactivators were characterised by dissociation constant of enzyme-reactivator complex as well as enzyme-inhibitor-reactivator complex and by rate constant of reactivation.

Biochemical effects of low level exposure to soman vapour.

The aim of this study was to demonstrate changes in acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities, tyrosine aminotransferase activity (TAT) and plasma corticosterone level, neuroexcitability and behavior following 24 hours and 4 weeks of soman sublethal inhalation exposure at low level. AChE activity in erythrocytes and BuChE activity in plasma was decreased (dependent on the concentration of soman) 24 h and 4 weeks after the exposure. Similar decrease in AChE activity in different brain parts was observed. One of stressogenic parameters (TAT) was changed after 24 h exposure only. 4 weeks after the exposure, these parameters (corticosterone and TAT) were in the range of normal values. Behaviour of experimental animals was changed 24 h after the exposure persisting 4 weeks after the exposure as well as neuroexcitability.

The influence of low-level sarin inhalation exposure on the host resistance and immune reaction of inbred BALB/c mice after their infection with Francisella tularensis LVS.

To study the influence of low-level sarin inhalation exposure on immune functions, inbred BALB/c mice were exposed to two low concentrations of sarin for 60 minutes in the inhalation chamber and then infected with Francisella tularensis LVS on the 7th day following the exposure to sarin. 24 hours after infection, the level of some isotypes of antibodies (IgM, IgA) against tularaemia was significantly decreased regardless of the sarin concentration used while the lymphoproliferation was significantly increased regardless of the mitogen and sarin concentration used. Later, the level of some isotypes of antibodies (IgM, IgA) against tularaemia and the vitality of Francisella tularensis LVS was significantly increased in the case of exposure of mice to clinically symptomatic concentration of sarin (7 days after infection) while the lymphoproliferation was significantly decreased regardless of the concentration of sarin when specific tularaemic antigen Ag4 was used as a mitogen (3 weeks after infection). Thus, the results indicate that not only symptomatic but also asymptomatic dose of sarin is able to alter the host resistance and reaction of immune system, especially at 24 hours and 7 days following infection with Francisella tularensis LVS. Nevertheless, the alteration of immune functions following the inhalation exposure to a symptomatic concentration of sarin seems to be more pronounced.

Acute experimental tabun-induced intoxication and its therapy in rats.

Pharmacological pretreatment and antidotal treatment on tabun-induced neurotoxicity were studied in male albino rats that were poisoned with a lethal dose of tabun (280 microg/kg i.m.; 100% of LD50 value) and observed at 24 hours and 7 days following tabun challenge. The neurotoxicity of tabun was evaluated using a Functional observational battery and an automatic measurement of motor activity. Pharmacological pretreatment as well as antidotal treatment were able to reverse most of tabun-induced neurotoxic signs observed at 24 hours following tabun poisoning. However, there was not significant difference between the efficacy of profylaxis and antidotal treatment to eliminate tabun-induced neurotoxicity. The combination of profylactic pretreatment and antidotal treatment seems to be slightly more effective in the elimination of tabun-induced neurotoxicity in rats at 24 hours following tabun challenge in comparison with the administration of profylactic pretreatment or antidotal treatment alone. At 7 days following tabun poisoning, very few neurotoxic signs in tabun-poisoned rats were observed regardless of administration of pharmacological pretreatment or antidotal treatment. Thus, our findings confirm that the combination of pharmacological pretreatment and antidotal treatment is not only able to protect the experimental animals from the lethal effects of tabun but also to eliminate most of tabun-induced signs of neurotoxicity in tabun-poisoned rats.

[Effect of acetylcholinesterase reactivator dosage on its effectiveness in the treatment of tabun poisoning in mice]. / Vliv dávky reaktivátoru acetylcholinesterasy na jejich úcinnost pri terapii otravy mysí tabunem.

The therapeutic efficacy of selected reactivators of acetylcholinesterase (obidoxime, oxime HI-6, trimedoxime) against acute tabun poisoning in dependence on their dose was examined in experiments on male mice. A comparison of the values of the medium lethal dose (LD50) of tabun in the intoxication influenced by an antidote therapy consisting of atropin and some of the oximes tested revealed that in all three oximes under study their dose markedly influenced their effect. The highest efficacy was always achieved when oximes were administered in the maximal therapeutic dose (20% of LD50). It follows from the comparison of the efficacy of equieffective doses of the oximes tested that in all doses the acute lethal effects of tabun are most effectively eliminated by trimedoxime, and on the other hand, obidoxime seems to be least effective, though in the smallest dose tested (2% of LD50) the differences between the therapeutic efficacy of the individual oximes are not statistically significant. Oxime HI-6 is significantly more effective than obidoxime (in a dose corresponding to 20% of LD50), but it is less effective than trimedoxime (in a dose corresponding to 5% LD50). The achieved results have shown that oxime HI-6, so effective against soman, another nerve agent, is not the most advantageous reactivator of acetylcholinesterase for the therapy of acute tabun poisonings, though its efficacy is partly eliminated by its possible higher dosing in human medicine due to its lower toxicity for mammals. The most suitable reactivator of acetylcholinesterase for the elimination of acute lethal toxic effects of tabun seems to be trimedoxime. Obidoxime, which is the most widely used reactivator of acetylcholinesterase in the therapy of poisonings by nerve agents at present, is, like in the case of soman poisonings, a relatively least suitable oxime ensuring the survival in lethal tabun poisonings.

A comparison of the decontamination efficacy of foam-making blends based on cationic and nonionic tensides against organophosphorus compounds determined in vitro and in vivo.

The ability of foam-making blends to decontaminate the skin exposed to organophosphorus compounds was tested. The appropriate composition and rheological features (stability, grade of foaming) of tested blends were evaluated by in vitro methods and their ability to remove the contaminants from hard surface and to transform the contaminants into nontoxic compounds was evaluated by in vivo methods. The blends containing cationic and nonionic tensides as well as alkalized hydrogen peroxide seem to be the most efficacious to decontaminate the skin exposed to organophosphorus compounds according to the literature data. The composition of tested blends was optimized because particular components often have antagonistic effects. Cationic tensides support the reactivity of the blend and control the grade of foaming. Nonionic tensides control the stability of the foams but also react as retardants of the reactivity of the foams. Hydrogen peroxide is a real reacting component when it is transformed into hydrogen peroxide anion. It also acts as buffer if pH is higher than 11. Our in vivo results confirm that Desam OX (34 and 68%) and the foam-making blend containing benzalkonium chloride--Althosan MB (8%), Slovasol 2510 (2%) and hydrogen peroxide (3%) alkalized at pH 12 seem to be the most efficacious to remove contaminants (soman, VX) from the skin and transform them into nontoxic compounds. Therefore they could be used for primary decontamination of chemical casualties contaminated with nerve agents in the field condition.