hgg-12 and asoxime-chloride

The oximes HI-6, HLö-7, HGG-12, HGG-42 and obidoxime were used in a previously developed rat model to evaluate the therapeutic effects of oximes other than acetylcholinesterase (AChE) reactivation (so-called "non-reactivating effects"). To test this anaesthetized, atropinized and artificially ventilated rats (n = 8 or 16) were poisoned with a three times LD50 dose of the potent AChE-inhibitor crotylsarin (CRS, i.v.). CRS-inhibited rat AChE dealkylates instantaneously, thereby excluding AChE reactivation by the oximes. Five minutes after poisoning the rats were treated (i.v.) with an oxime or saline and 10 min later artificial ventilation was terminated. Survival times were determined. Saline-treated animals died within 15 min. In comparison, treatment with HI-6, HLö-7, HGG-12, HGG-42 or obidoxime resulted in a significant prolongation of survival time. In the groups treated with HLö-7, HI-6 or HGG-12, 12-37% of the animals survived more than 24 h. It was investigated whether differences in therapeutic effectiveness are caused by differences in pharmacokinetics of the oximes. The plasma half-lives of HI-6, HLö-7, HGG-12, HGG-42 and obidoxime amounted to 67, 63, 27, 55 and 179 min, respectively. At doses of 75 or 150 mumol/kg, all oximes could be detected in brain and medulla oblongata in similar amounts (6-10 nmol/g tissue). In vitro, all oximes were effective in restoring failure of neuromuscular transmission (NMT) caused by CRS, albeit with varying potency. All oximes bound with affinities in the micromolar range to rat brain muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Binding, Competitive; Brain; Cholinesterase Inhibitors; Cholinesterase Reactivators; In Vitro Techniques; Male; Neuromuscular Junction; Obidoxime Chloride; Oximes; Pyridines; Pyridinium Compounds; Quinuclidinyl Benzilate; Rats; Sarin; Synaptic Transmission

Isolated rat diaphragm preparations treated with soman or with the irreversible and oxime resistant cholinesterase (ChE) inhibitor S27 showed a considerable recovery of neuromuscular transmission (NMT) during incubation with the (bis)pyridinium oximes HI-6, HGG-12, P2S and obidoxime. In the soman-treated preparations this NMT recovery was predominantly caused by reactivation of acetylcholinesterase (AChE) but in the S27-treated preparations it was caused by a direct (pharmacological) effect unrelated to enzyme reactivation. Atropinized rats were artificially ventilated after injection with 3 x LD50 soman for 3 h and then treated with HI-6, i.e. at a time when oxime reactivation of soman inhibited ChE is no longer possible. Nevertheless, these rats started to breathe spontaneously and 50-60% survived more than 24 h, whereas all control animals (saline instead of HI-6) died within 10 min after artificial ventilation was terminated. In such animals no significant reactivation of ChE activity at various time intervals following HI-6 treatment was found, either in the diaphragms or in the brains. There was a significant amount of NMT (50%) in vitro in diaphragms obtained from these animals. This NMT did not improve in vitro in the presence of HI-6 and was not inhibited by soman administered to the medium. It is concluded that in this case the NMT found was based on synaptic adaptation to the continued inhibition of ChE and that the survival of the animals might be due to a combination of this synaptic adaptation and central direct effects of HI-6.

Topics: Animals; Antidotes; Blood-Brain Barrier; Cholinesterase Reactivators; Diaphragm; In Vitro Techniques; Male; Neuromuscular Junction; Obidoxime Chloride; Organophosphate Poisoning; Oximes; Pralidoxime Compounds; Pyridinium Compounds; Rats; Respiratory Insufficiency; Synaptic Transmission

HI 6(pyridinium, 1-[[[4-(aminocarbonyl)pyridinio]methoxy]-2- [(hydroxyimino)methyl]-dichloride belongs to a series of bisquaternary pyridinium oximes that are effective against poisoning with extremely toxic organophosphates. Since HI 6 has been shown to be unstable at pH 7.4 and to release significant amounts of cyanide, a study was undertaken to determine the degree of cyanide formation from HI 6 in vivo. When HI 6 (100 mumol/kg) was administered i.v. to dogs, the animals showed no signs of cyanide toxicity but exhibited some cholinomimetic symptoms, including retching, hypersalivation and enhanced intestinal motility. Cyanide content in whole blood was monitored after production of methemoglobinemia (30%) by 4-dimethylaminophenol in order to sequester cyanide within red cells. Maximal cyanide contents of 20 mumol/l were found in blood after 90 min. Calculation of the area under the concentration versus time curve for blood cyanide indicates that about 4% of HI 6 produced cyanide. Determination of the pharmacokinetic parameters of HI 6 (VD = 0.31 l/kg; kel = 0.76 h-1) and of cyanide (VD = 0.086 l/kg; kel = 0.52 h-1) together with the apparent first order rate constant of cyanide formation from HI 6 in vitro (0.17 h-1, pH 7.4, 37 degrees) allowed the simulation of a cyanide concentration curve that fitted with the experimental data points, indicating that cyanide formation in vivo was not bio-catalyzed. It is concluded that cyanide formation from HI 6 may not be regarded as a potential hazard, since cyanide elimination exceeded markedly its formation. Whether this conclusion also holds true for man has to be established.

Topics: Aminophenols; Animals; Antidotes; Cyanides; Dogs; Injections, Intravenous; Male; Methemoglobin; Oximes; Pyridinium Compounds

Topics: Acetylcholinesterase; Animals; Central Nervous System; Chemical Warfare; Cholinesterase Inhibitors; Cholinesterase Reactivators; Gas Poisoning; Organophosphate Poisoning; Organophosphates; Oximes; Pyridinium Compounds; Rats; Sarin; Soman

The mode of interaction of bisquaternary pyridinium oximes with rat brain muscarinic receptors in cerebral cortex and brain stem preparations was studied by the use of the tritium-labeled antagonist N-methyl-4-piperidyl benzilate ( [3H] 4NMPB). Binding of the labeled muscarinic antagonist was inhibited by these drugs, the most potent inhibitors being 1-(2-hydroxyiminoethylpyridinium)-1-(3-cyclohexylcarboxypyridin ium)dimethyl-ether (HGG-42) and its 3-phenylcarboxypyridinium analog (HGG-12) (apparent KI = 1.3-1.7 and 1.8-2.2 microM, respectively). Analysis of the binding properties suggested that binding of the muscarinic antagonist and the bisquaternary pyridinium oximes was nonexclusive. Kinetic binding data provide evidence that the drugs inhibit binding of muscarinic antagonists in an allosteric manner, with a resulting decrease in the rates of both association of [3H]4NMPB to the receptor and its dissociation from it. These effects were observed both in brain stem and in cortical preparations even after pretreatment and washing out of the inhibitors. The selective natures of HGG-12 and HGG-42 were apparent from their irreversible effects on the number of muscarinic binding sites. In brain stem, the presence of these drugs resulted in a loss of about 30% of binding sites, which accounts in part for the apparent decrease in maximal binding capacity observed in the equilibrium binding of [3H]4NMPB. In the cortex, however, only approximately 10% of the muscarinic receptors were lost upon exposure to these drugs. The decrease in the muscarinic receptor population of the brain stem was dependent on both concentration and time and occurred both in vitro and in vivo following injection of HGG-12 into rats. Unlike the in vitro loss of receptor sites, which was irreversible, the in vivo effect was restored 2 hr after the injection. Taken together, the results suggest that the bisquaternary oximes are allosteric inhibitors of the muscarinic acetylcholine receptor and may be capable of distinguishing between receptor states and inducing specific irreversible effects. Because of these properties, the drugs may prove extremely useful as sensitive probes in studies on the nature of the agonist-receptor-effector relationship.

Topics: Animals; Benzilates; Brain; Dose-Response Relationship, Drug; Kinetics; Mathematics; Obidoxime Chloride; Oximes; Piperidines; Pyridinium Compounds; Rats; Receptors, Muscarinic

The role of the functional substituents on the pyridinium ring of bisquaternary pyridinium compounds, mostly oximes, in exerting reversible and irreversible inhibition of binding of [3H]-N-methyl-4-piperidyl benzilate [( 3H]-4NMPB) to rat brain stem muscarinic receptors was studied. The drugs tested, i.e. HGG-42, HGG-12, HGG-52, HI-6, obidoxim, SAD-128 and TMB-4, could reversibly inhibit binding of [3H]-4NMPB, with the highest potency (KI = 1.7 - 6 microM) exhibited by analogs possessing hydrophobic substituents at position 3 or 4 of the pyridinium ring. Bisquaternary drugs possessing an oxime moiety at position 2, but not at position 4 of the pyridinium ring, could also induce about 30% reduction of maximal binding capacity (Bmax) (loss of muscarinic receptors) in addition to their reversible effect. Thus the structural correlates of the reversible and the irreversible effects of these drugs are different.

Topics: Animals; Benzilates; Binding, Competitive; Brain Stem; Cell-Free System; Obidoxime Chloride; Oximes; Parasympatholytics; Piperidines; Pyridinium Compounds; Rats; Receptors, Muscarinic; Structure-Activity Relationship; Trimedoxime

It has been shown that HI-6 was the most potent oxime so far known in poisoning by sarin, VX , and soman, but its protective effect in tabun poisoning, allegedly due to poor reactivation of inhibited ChE, was much less pronounced. We have found that the thiocholine-like analog of tabun , O-ethyl, N-N- dimethyamino -S-(2-diethylaminoethyl)- thiophosphatemethylsul fomethylate (Ta-S-N+), was very useful in resolving this problem and established the relationship between reactivating and protective effects of PAM-2 Cl, HI-6, and HGG-12 in rats. PAM-2 Cl (protective ratio (PR) = 22.1) and HI-6 (PR = 24.8), combined with atropine, were very effective against Ta-S-N+ poisoning and reactivating inhibited RBC AChE in vitro and rat blood ChE in vivo. The inefficiency of PAM-2 Cl (PR = 1.6) and HI-6 (PR = 2) in tabun poisoning was due to their inadequacy to reactive tabun -inhibited ChEs . The protective effects of HGG-12 in tabun (PR = 2.8) and Ta-S-N+ poisoning (PR = 2.6) were low, and in the absence of any reactivation of inhibited ChEs , have been attributed to its direct pharmacological effects, which were much more potent in the comparison with PAM-2 Cl or HI-6. It is concluded that the reactivation of inhibited ChE is of decisive importance in the efficient protection in poisoning by tabun and other known chemical warfare nerve agents, whereas their direct pharmacological effects are of limited value, allowing survival of animals only against a few LD50s .

Topics: Animals; Atropine; Choline; Cholinesterase Reactivators; Cholinesterases; Female; Guinea Pigs; Heart; Humans; Lethal Dose 50; Male; Muscle Contraction; Muscle, Smooth; Organophosphate Poisoning; Organophosphates; Oximes; Phrenic Nerve; Pralidoxime Compounds; Pyridinium Compounds; Rats; Thiocholine

Acute sc toxicity of soman increased in the order, mice----rats----guinea pigs----dogs, being 12.6 times more toxic to dogs (LD50 = 0.05 mumol/kg) than to mice. It was 2.8 times more toxic than tabun to mice and 35 times more toxic to dogs. HI-6 was the least toxic and had similar toxicity values to the four animal species studied and HGG-12 the most toxic of the three oximes used. HGG-12 has shown the greatest interspecies variation (rats:dogs = 1:19.5). HI-6, HGG-12, and PAM-2 Cl (in conjunction with atropine and diazepam) revealed the best protective effect in soman-poisoned dogs, with the respective protective indices of 9, 6.3, and 3.5, followed by guinea pigs. In tabun poisoning the best, but relatively low, protective effect was found only in guinea pigs. The introduction of diazepam increased the protective effects of atropine-oxime combination in soman and tabun poisoning by 10 to 80%. We suggest that the high toxicity of soman and low toxicity of HI-6 may be anticipated in man. The inefficiency of HI-6, HGG-12, and PAM-2 Cl in tabun poisoning points either to the search of new compounds or to the use of the mixture of the oximes found to be effective against the known chemical warfare nerve agents.

Topics: Acetylcholinesterase; Animals; Antidotes; Atropine; Cholinesterase Inhibitors; Cholinesterase Reactivators; Diazepam; Dogs; Guinea Pigs; Lethal Dose 50; Male; Mice; Organophosphate Poisoning; Organophosphates; Oximes; Pralidoxime Compounds; Pyridinium Compounds; Rats; Soman; Species Specificity

1 The ability of various bis-pyridinium oximes to restore organophosphate-inhibited neuromuscular transmission in vitro was compared in human intercostal and marmoset diaphragm muscles. 2 HI-6 (2-hydroxyiminomethyl-pyridinium-1-methyl-4'-carbamoyl-pyridinium-1'-methyl ether dichloride monohydrate) appeared very effective against VX (O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate) and sarin in both muscles, whereas obidoxim was quite effective against tabun. 3 Against soman, HI-6, HS-6 (2-hydroxyiminomethyl-pyridinium-1-methyl-3'-carbamoyl-pyridinium-1'-methyl ether dichloride dihydrate) and obidoxim had little effect in the human muscle and only slight activity in the marmoset muscle; HGG-12 (2-hydroxyiminomethyl-pyridinium-1-methyl-3'-phenylcarbonyl-pyridinium-1'-methy l ether dichloride) and benzyl-P2A (1-benzyl-2-hydroxyiminomethyl-pyridinium methanesulphonate) were ineffective. 4 Anaesthetized, atropinized marmosets were poisoned with soman (4 X LD50, i.v.) and subsequently treated with HI-6, HS-6 or HGG-12. Only HI-6 and HS-6 were marginally effective in restoring respiration and neuromuscular transmission. 5 Marmoset muscle is a reasonable model for human muscle for the study of organophosphate poisoning and therapy.

Topics: Animals; Antidotes; Callithrix; Cardiovascular System; Humans; In Vitro Techniques; Insecticides; Models, Biological; Neuromuscular Junction; Oximes; Pralidoxime Compounds; Pyridinium Compounds; Soman; Synaptic Transmission

HI-6 and TMB-4 were the most effective and safe of 7 cholinesterase reactivators tested as agents for the prophylaxis of proserine poisoning of male mice. The reactivator HI-6 strongly potentiated the prophylactic efficacy of a mixture of atropine and arpenal administered in the doses sufficient for the blockade of both the m- and h-cholinoreactive systems of mice. As demonstrated by experiments in vitro, HI-6 and TMB-4 did not reacivate proserine-inhibited cholinesterase. The natural anticholinesterase activity of HI-6 was negligible. Based on the correlation of the data obtained to the reported data indicating that HI-6 has a low ganglioblocking activity it is inferred that the direct effect on the receptor is of no importance for the potentiating effect. It is assumed that HI-6 modulates the cholinoreactive systems, which leads to a dramatic increase of the efficacy of cholinolytics.

Topics: Animals; Antidotes; Atropine; Butanones; Cholinesterase Reactivators; Diphenylacetic Acids; Drug Synergism; Male; Mice; Neostigmine; Obidoxime Chloride; Oximes; Parasympatholytics; Pralidoxime Compounds; Pyridinium Compounds; Trimedoxime