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PubMed2005

Evaluation of oxime efficacy in nerve agent poisoning: development of a kinetic-based dynamic model.

The widespread use of organophosphorus compounds (OP) as pesticides and the repeated misuse of highly toxic OP as chemical warfare agents (nerve agents) emphasize the necessity for the development of effective medical countermeasures. Standard treatment with atropine and the established acetylcholinesterase (AChE) reactivators, obidoxime and pralidoxime, is considered to be ineffective with certain nerve agents due to low oxime effectiveness. From obvious ethical reasons only animal experiments can be used to evaluate new oximes as nerve agent antidotes. However, the extrapolation of data from animal to humans is hampered by marked species differences. Since reactivation of OP-inhibited AChE is considered to be the main mechanism of action of oximes, human erythrocyte AChE can be exploited to test the efficacy of new oximes. By combining enzyme kinetics (inhibition, reactivation, aging) with OP toxicokinetics and oxime pharmacokinetics a dynamic in vitro model was developed which allows the calculation of AChE activities at different scenarios. This model was validated with data from pesticide-poisoned patients and simulations were performed for intravenous and percutaneous nerve agent exposure and intramuscular oxime treatment using published data. The model presented may serve as a tool for defining effective oxime concentrations and for optimizing oxime treatment. In addition, this model can be useful for the development of meaningful therapeutic animal models.

Acetylcholine↗
PubMed1979

[On the plurifactorial determinism of the organophosphorous-induced teratogenesis on bird embryos; trials of protection by various compounds: oximes, hydroxamic acids and nicotinamide analogs (author's transl)].

Simple methods were applied to study the teratogenesis in Quail embryos induced by two important organophosphorous compounds: parathion and dicrotophos. Parathion led only to vertebral malformations, as other natural and synthetic cholinomimetics: nicotine, carbamylcholine, decamethonium, neostigmine... Dicrotophos induced not only vertebral malformations (specific to neuromuscular junction poisons) but also beak, legs and feather abnormalities (peripheric malformations which are also produced by insuline and sulfanilamide). Oximes and hydroxamic acids, some of these being analogs of nicotinamide, were tested as antiteratogens. The 3-(CO-NH2), or -(CO-NHOH), substituted pyridinic compounds (nicotinamide, nicotinohydroxamic acid) prevent perfectly dicrotophos-induced beak and legs malformations, in tertiary amine form, but very little in quaternary amine form (methyliodide). The 4-substituted pyridinic compound (isonicotinohydroxamic acid) and aliphatic oxo-oximes were quite ineffecient against these malformations. The vertebral malformations, as a rule, were not lessened by the compounds tested, except for isonicotinoyl-formaldoxime methyl iodide and in some degree for nicotinohydroxamic acid. From these observations, it results that teratogenesis induced by compounds as dicrotophos is rule by a plurificatorial determinism. The beak and legs malformations are prevented by analogs of nicotinamide. In the contrary, the vertebral malformations induced by parathion or dicrotophos are nicotinamide unsensitive and are only prevented by powerful cholinesterase reactivators as pralidoxime or TMB4 (MEINIEL, 1976 b) but are reduced little or not at all by less potent cholinesterase reactivators (HEATH).

Abnormalities, Drug-Induced↗
PubMed2004

In vitro reactivation of tabun-inhibited acetylcholinesterase using new oximes--K027, K005, K033 and K048.

Four new AChE oximes for reactivation of acetylcholinesterase inhibited with tabun - K027 [1-(4-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium) propane dibromide], K005 [1,3-bis(2-hydroxyiminomethylpyridinium) propane dibromide], K033 [1,4-bis(2-hydroxyiminomethylpyridinium) butane dibromide] and K048 [1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide] were prepared. Their efficacies to reactivate tabun-inhibited acetylcholinesterase were studied and compared with the currently used acetylcholinesterase reactivators (pralidoxime, obidoxime and HI-6). Reactivator K048 seems to be promising reactivator of tabun-inhibited AChE. Its reactivation potency is significantly higher than the efficacy of HI-6 and pralidoxime, and comparable with the potency of the obidoxime at human relevant doses.

Animals↗
PubMedDate not supplied

Diagnosis and treatment of organophosphate and carbamate intoxication.

Organophosphate and carbamate insecticides are the most common forms of pesticide poisoning. They present with a distinctive clinical syndrome that is, nevertheless, sometimes difficult to recognize. Early treatment is important, and specific antidotal therapy is available using atropine and pralidoxime. Important complications that need to be monitored during therapy may involve the central and peripheral nervous system, lungs, and heart.

Carbamates↗
PubMed1997

Cholinesterase status, pharmacokinetics and laboratory findings during obidoxime therapy in organophosphate poisoned patients.

1 The effectiveness of oxime therapy in organophosphate poisoning is still a matter of debate. It appears, however, that the often cited ineffectiveness of oximes may be due to inappropriate dosing. By virtue of in vitro findings and theoretical considerations we concluded in the preceding paper that oximes should preferably be administered by continuous infusion following an initial bolus dose for as long as reactivation of inhibited acetylcholinesterase (AChE) can be expected. This conclusion has called for a clinical trial to evaluate such oxime therapy on the basis of objective parameters. 2 Before transfer to the intensive care unit (ICU), 5 patients received primary care by an emergency physician. In the ICU, atropine sulphate was administered i.v. upon demand according to the endpoints: no bronchorrhoea, dry mucous membranes, no axillary sweating, heart rate of about 100/min. Obidoxime (Toxogonin) was given as an i.v. bolus (250 mg) followed by continuous infusion of 750 mg/24 h. 3 Intoxication and therapy were monitored by determining erythrocyte AChE (eryAChE) activity, reactivatability of the patient's eryAChE ex vivo, plasma cholinesterase activity, the presence of AChE inhibiting compounds, as well as the concentrations of obidoxime and atropine in plasma. 4 Obidoxime was effective in life-threatening parathion poisoning, in particular when the dose absorbed was comparably low. In mega-dose poisoning, net reactivation was not achieved until several days after ingestion, when the concentration of active poison in plasma had declined. Reactivatability in vivo lasted for a longer period than expected from in vitro experiments. 5 Obidoxime was quite ineffective in oxydemetonmethyl poisoning, when the time elapsed between ingestion and oxime therapy was longer than 1 day. When obidoxime was administered shortly after ingestion (1 h) reactivation was nearly complete. 6 Obidoxime levels of 10-20 microM were achieved by our regimen, and atropine could rapidly be reduced to approx. 20 microM, as attained by continuous infusion of 1 mg atropine sulphate/h. Maintenance of the desired plasma levels was not critical even when renal function deteriorated. 7 Signs of transiently impaired liver function were observed in patients who showed transient multiorgan failure. In the present stage of knowledge, we feel it advisable to keep the plasma concentration of obidoxime at 10-20 microM, although the full reactivating potential of obidoxime will not then be exploited. Still, the reactivation rate, with an apparent half-time of some 3 min, is twice that estimated for a tenfold higher pralidoxime concentration.

Acetylcholinesterase↗
PubMed1996

Reactivation by various oximes of human erythrocyte acetylcholinesterase inhibited by different organophosphorus compounds.

The new bispyridinium oximes HI 6 and HLö 7 are promising antidotes against poisoning by highly toxic organophosphorus compounds, i.e. nerve agents. Until now, their ability to reactivate pesticide inhibited human acetylcholinesterase (AChE) has not been elucidated. For this purpose human erythrocyte AChE (EC 3.1.1.7) was inhibited (30 min) by chlorfenvinphos, dichlorvos, dicrotophos, heptenophos, mevinphos, monocrotophos, paraoxon, phosphamidon, trichlorfon, malaoxon, omethoate, oxydemeton-methyl or methamidophos by 85-98% of control. After removal of excess inhibitor, obidoxime, pralidoxime (2-PAM), HI 6 or HLö 7 (10, 30 or 100 mumol/l) were added and the AChE activity was measured spectrophotometrically at various times thereafter (5-60 min). The oximes significantly, but not completely, reactivated organophosphate inhibited AChE. The velocity and extent of reactivation were dependent on the oxime and its concentration. In all cases obidoxime was superior to the three other oximes, followed by HLö 7, 2-PAM and HI 6. In most cases obidoxime and HLö 7 were most effective at 10 or 30 mumol/l while 2-PAM and HI 6 needed 100 mumol/l. These data suggest that 2-PAM HI 6 and HLö 7 are less patent than obidoxime in reactivating human AChE inhibited by organophosphate pesticides.

Acetylcholinesterase↗
PubMedDate not supplied

Bispyridinium oximes as antidotal treatment of cyclosarin poisoning-in vitro and in vivo testing.

The mechanism of intoxication with organophosphorus compounds, including highly toxic nerve agents and less toxic pesticides, is based on the formation of irreversibly inhibited acetylcholinesterase, which causes cumulation of neuromediator acetylcholine in synaptic clefts and subsequent overstimulation of cholinergic receptors, that is followed by a generalized cholinergic crisis. Nerve agent poisoning is conventionally treated using a combination of a cholinolytic (atropine mostly) to counteract the accumulation of acetylcholine and acetylcholinesterase reactivators (pralidoxime or obidoxime) to reactivate inhibited acetylcholinesterase. In this study of cyclosarin poisoning treatment, oximes of different chemical structures (obidoxime, HI-6, BI-6, and HS-6) were tested in vitro on rat brain acetylcholinesterase (enzyme source: rat brain homogenate), and afterwards, they were tested in vivo in equimolar doses, in mice and rats. The HI-6 oxime appeared to be the most effective oxime in vitro and in vivo.

Animals↗
PubMed2005

A comparison of the potency of trimedoxime and other currently available oximes to reactivate tabun-inhibited acetylcholinesterase and eliminate acute toxic effects of tabun.

Tabun (O-ethyl-N,N-dimethyl phosphoramidocyanidate) belongs to highly toxic organophosphorus compounds misused as chemical warfare agents for military as well as terroristic purposes. It differs from other highly toxic organophosphates by its chemical structure and by the fact that tabun-inhibited acetylcholinesterase is extraordinarily difficult to reactivate. The potency of trimedoxime and other commonly used oximes (pralidoxime, obidoxime, the oxime HI-6) to reactivate tabun-inhibited acetylcholinesterase and to eliminate tabun-induced acute effects was evaluated using in vitro and in vivo methods. In vitro calculated kinetic parameters of reactivation of tabun-inhibited acetylcholinesterase from rat brain homogenate and in vivo determined percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in poisoned rats show that trimedoxime seems to be the most efficacious reactivator in the case of tabun poisonings. Trimedoxime was also found to be the most efficacious oxime in the elimination of acute lethal toxic effects in tabun-poisoned rats and mice. The oxime HI-6, so efficacious against soman, does not seem to be sufficiently effective oxime to reactivate tabun-inhibited acetylcholinesterase and to counteract acute lethal effects of tabun.

Acetylcholinesterase↗
PubMed2006

Application of kinetic-based computer modelling to evaluate the efficacy of HI 6 in percutaneous VX poisoning.

The rife use of organophosphorus compounds (OP) as pesticides and the exertion of highly toxic OP-type chemical warfare agents (nerve agents) during military conflicts and terrorist attacks in the past emphasize the necessity of the development of effective therapeutic countermeasures. Presently, standard treatment of poisoning by OP includes administration of atropine as an antimuscarinic agent and of oximes, e.g. obidoxime or pralidoxime, as reactivators of OP-inhibited acetylcholinesterase (AChE), but is considered to be rather ineffective with certain nerve agents. The evaluation of new oximes as antidotes is only possible by implementation of animal experiments for ethical reasons and therefore complicated by a limited extrapolation of animal data to humans due to marked species differences. A computer simulation based on combination of AChE kinetic data (inhibition, reactivation, aging) with OP toxicokinetics and oxime pharmacokinetics allows the calculation of AChE activities at different scenarios and may facilitate to define effective oxime concentrations and to optimize oxime dosage in OP poisoning. On the base of species-specific kinetic data this model was used to calculate AChE activities in humans and pigs after percutaneous exposure to 5 x LD50 VX and treatment with HI 6. Due to marked species differences between human and pig AChE the HI 6 dose that is necessary to cause a comparable reactivation of VX-inhibited pig AChE is conspicuously higher. Hence, designing animal experiments with the aid of computer modeling may reduce the number of animal experiments and allow a more reliable extrapolation of animal data to humans.

Administration, Cutaneous↗
PubMed2005

Strategy for the development of new acetylcholinesterase reactivators - antidotes used for treatment of nerve agent poisonings.

The mechanism of intoxication with organophosphorus compounds, including highly toxic nerve agents, is based on the formation of irreversibly inhibited acetylcholinesterase (AChE; EC 3.1.1.7) that could be followed by a generalized cholinergic crisis. Nerve agent poisoning is conventionally treated using a combination of a cholinolytic drug (atropine mostly) to counteract the accumulation of acetylcholine at muscarinic receptors and AChE reactivators (pralidoxime or obidoxime) to reactivate inhibited AChE. At the Department of Toxicology, the strategy of the development of new more potent AChE reactivators consists of several steps: description of the nerve agent intoxication mechanism on the molecular basis (molecular design), prediction of the biological active structure of AChE reactivators (artificial neural networks), their synthesis, in vitro evaluation of their potencies (potentiometric titration and Ellman's method), in vivo studies (therapeutic index, LD(50) of newly synthesized reactivators, reactivation in different tissues, neuroprotective efficacy).

Chemical Warfare Agents↗
PubMed1992

Dizocilpine (MK-801) arrests status epilepticus and prevents brain damage induced by soman.

The involvement of the NMDA receptor in the neurotoxicity induced by soman, an organophosphorus compound which irreversibly inhibits cholinesterase, was studied in guinea pigs. The drug MK-801 (0.5, 1 or 5 mg/kg, i.p.) was given as a pretreatment before a convulsant dose of soman or as a posttreatment (30, 100 or 300 micrograms/kg, i.m.) 5 min after the development of soman-induced status epilepticus. Pyridostigmine, atropine and pralidoxime chloride were also given to each subject to counteract the lethality of soman. All subjects that were challenged with soman and given the vehicle for MK-801 (saline) exhibited severe convulsions and electrographic seizure activity. Neuronal necrosis was found in the hippocampus, amygdala, thalamus and the pyriform and cerebral cortices of those subjects surviving for 48 hr. Pretreatment with 0.5 or 1 mg/kg doses of MK-801 did not prevent nor delay the onset of seizure activity but did diminish its intensity and led to its early arrest. At the largest dose (5 mg/kg), MK-801 completely prevented the development of seizure activity and brain damage. Posttreatment with MK-801 prevented, arrested or reduced seizure activity, convulsions and neuronal necrosis in a dose-dependent manner. The NMDA receptor may play a more critical role in the spread and maintenance, rather than the initiation of cholinergically-induced seizure activity.

Amygdala↗
PubMed2005

New quaternary pyridine aldoximes as casual antidotes against nerve agents intoxications.

In this work, the ability of four newly synthesized oximes--K005 (1,3-bis(2-hydroxyiminomethylpyridinium) propane dibromide), K027 (1-(4-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium) propane dibromide), K033 (1,4-bis(2-hydroxyiminomethylpyridinium) butane dibromide) and K048 (1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide) to reactivate acetylcholinesterase (AChE, EC 3.1.1.7) inhibited by nerve agents is summarized. Reactivation potency of these compounds was tested using standard in vitro reactivation test. Tabun, sarin, cyclosarin and VX agent were used as appropriate testing nerve agents. Rat brain AChE was used as a source of the enzyme. Efficacies of new reactivators to reactivate tabun-, sarin-, cyclosarin- and VX-inhibited AChE were compared with the currently used AChE reactivators (pralidoxime, obidoxime and HI-6). Oxime K048 seems to be promising reactivator of tabun-inhibited AChE. Its reactivation potency is significantly higher than that of HI-6 and pralidoxime and comparable with the potency of obidoxime. The best reactivator of sarin-inhibited AChE seems to be oxime HI-6. None of the new AChE reactivators reached comparable reactivation potency. The same results were obtained for cyclosarin-inhibited AChE. However, oxime K033 is also potent reactivator of AChE inhibited by this nerve agent. In the case of VX inhibition, obidoxime and new oximes K027 and K048 seem to be the best AChE reactivators. None from the currently tested AChE reactivators is able to reactivate AChE inhibited by all nerve agents used and, therefore, the search for new potential broad spectrum AChE reactivators is needed.

Acetylcholinesterase↗
PubMed1991

Treatment of acute organophosphate poisoning.

The biochemistry and pharmacology of poisoning by organophosphorus esters and carbamates are outlined and methods of diagnosis and treatment are discussed. Treatment consists of reduction of exposure by decontamination, induction of vomiting or gastric lavage; pharmacological treatment with atropine and oximes (pralidoxime and obidoxime); and supportive treatment with artificial respiration and centrally acting drugs such as diazepam. The sequence of treatment depends solely on the severity of poisoning.

Antidotes↗
PubMed2002

Organophosphate poisoning.

Stay safe! Certain scenes and scenarios invite a greater degree of caution. Wear protective gear (Level B for decon) and make sure the patient is hazmat-naked prior to decontamination. Use tincture of green soap or household dishwashing soap to decontaminate your patient. Maintain the patient's airway using oral/nasal airways; intubate if indicated. Give high-flow oxygen by nonrebreather oxygen mask or, if intubated, with a bagh-valve mask. Treat for shock by maintaining the patient's body temperature, keeping them supine if they will tolerate it, and gaining i.v. access. Administer oxygen, atropine, pralidoxime chloride and diazepam as required. Notify the ED and transport rapidly. If it is a terrorist incident, get your patient and get out.

Decontamination↗
PubMed2006

Evaluation of HI 6 treatment after percutaneous VR exposure by use of a kinetic-based dynamic computer model.

The availability of highly toxic OP-type chemical warfare agents (nerve agents) and the exertion of organophosphorus compounds during military conflicts and terrorist attacks against civilians in the past underlines the necessity of an effective treatment regimen of OP-poisoning. Presently, standard treatment includes administration of an antimuscarinic agent (e.g. atropine) and a reactivator of inhibited AChE (oxime), but is considered to be rather ineffective with certain nerve agents due to low oxime effectiveness of the currently available oximes, obidoxime and pralidoxime. The evaluation of new oximes as antidotes relies on the implementation of animal experiments for ethical reasons and is complicated by a limited extrapolation of animal data to humans. The development of a reliable animal model might accelerate the evaluation of new substances and their approval as antidotes, whereas, the pig as higher mammalian species seems to be promising as model animal. A dynamic in vitro model, which allows the calculation of AChE activities at different scenarios was developed to facilitate the definition of effective oxime concentrations and the optimization of oxime treatment of OP poisoning of humans and may furthermore be helpful by designing animal experiments. The model is based on a combination of enzyme kinetics (inhibition, reactivation, aging) of AChE with OP, toxicokinetics and oxime pharmacokinetics. By considering species-specific kinetic data this dynamic model was used for the calculation of AChE activities in humans and pigs after percutaneous exposure with 5x LD(50) VR (Russian VX) and treatment with HI 6, a promising new reactivator of OP-inhibited AChE. Due to a low affinity of HI 6 with VR-inhibited pig AChE the oxime dose that causes maximal reactivation of VR-inhibited pig AChE is conspicuously higher compared to humans. Therefore, the design of animal experiments in consideration of calculated data based on species-specific kinetic values may lead to a more reliable extrapolation of animal data to humans and may reduce the number of necessary animal experiments.

Administration, Cutaneous↗
PubMed1990

Toxicity of ethion in goats.

Cholinesterase activities were measured in plasma and in red blood cells from 6 goats after iv injection of the organophosphorus insecticide ethion at 3 different dose levels--2 mg/kg, 5 mg/kg and 10 mg/kg. Plasma levels of ethion after injection were established. At 2 mg/kg no signs of toxicity were observed and the blood cholinesterase activity remained above 65% of the control value. After administration of the higher doses the goats showed signs of severe toxicity corresponding to increased parasympathetic stimulation. Cholinesterase activities in blood were reduced to approximately 10% of the control value for the 5 mg/kg group and to approximately 5% for the 10 mg/kg group. Reactivation of cholinesterase activity in blood cells and plasma by means of pralidoxime was very efficient during the first 24 hr after administration of ethion, but was insignificant after 72 hours.

Animals↗
PubMed1994

Avian embryonic brain reaggregate culture system. II. NTE activity discriminates between effects of a single neuropathic or nonneuropathic organophosphorus compound exposure.

Biochemical responses after a single exposure to either a neuropathic or a nonneuropathic organophosphorus compound (OP) were compared using chick embryonic brain cell reaggregates. Ten-day-old chick embryo brains were dissociated and then reaggregated and maintained in a chemically defined, serum-free medium without antibiotics. Seven days later, these cultures were treated for 20 min with either neuropathic diisopropyl phosphorofluoridate (DFP, 10(-4) M) or nonneuropathic paraoxon (10(-6) M). Reaggregates were assayed for acetylcholinesterase (ACHE), neuropathy target esterase (NTE), and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) activities for up to 32 days after exposure. These enzymes were examined due to inhibition of activity as a result of acute OP toxicity (ACHE) or delayed toxicity (NTE, CNP). DFP inhibited > 95% of NTE activity immediately after exposure. By Postexposure Day 2, NTE specific activity was 22% of untreated activity but was similar to the untreated group levels by Postexposure Day 7. Paraoxon exposure did not affect NTE activity. Both paraoxon and DFP inhibited > 99% of ACHE activity immediately after exposure. By Postexposure Day 2, ACHE specific activity in paraoxon-exposed cultures had recovered while ACHE remained 56% inhibited in DFP-exposed cultures. Both paraoxon- and DFP-exposed cultures recovered ACHE activity immediately following OP exposure if treated postexposure with an oxime reactivator, 2-pralidoxime. CNP specific activity was not affected by either paraoxon or DFP. These results demonstrated distinct differences in reaggregate NTE and ACHE activities after single exposure to neuropathic DFP and nonneuropathic paraoxon similar to those in avian in vivo assays.

Acetylcholinesterase↗
PubMed2004

1,3-Bis(2-hydroxyiminomethylpyridinium) propane as the potential reactivator of the acetylcholinesterase inhibited by nerve agents.

The oxime K005 [1,3-bis(2-hydroxyiminomethylpyridinium) propane dibromide] for the reactivation of the enzyme acetylcholinesterase (AChE) inhibited by cyclosarin and VX was tested. Its reactivation potency was not better in comparison with the currently used AChE reactivator--pralidoxime. On the other hand, the oxime K005 has its maximum reactivation ability at the concentration 10(-4) M, which could be achieved for human use. The maximum concentration of pralidoxime was reached at the concentrations 10(-1) M (for cyclosarin) and 10(-3) M (for VX) but these concentrations are not available for the use in vivo.

Acetylcholinesterase↗