Soman Poisoning Research Articles

Cytophotometric analyses of brain neuronal RNA in soman intoxicated rabbits

Quantitative azure B-RNA cytophotometry was used to monitor metabolic responses of individual neurons of the motor cortex (layer V) and caudate nucleus of soman (pinacolyl methylphosphonofluoridate) poisoned rabbits. Time- and dose-dependent RNA responses were related to the extent of acetylcholinesterase (AChE) inactivation of these 2 brain regions and to overt behavioral manifestations of toxication. A complex pattern of RNA responses was evidenced, with RNA depletion occuring at both arousal and convulsive doses of soman. In general, RNA changes paralleled previously reported metabolic responses observed in soman toxicated rats and mice: (1) linear dose-dependent suppression of RNA was evidenced during the depressant phase but not in the acute excitatory phase of toxication; and (2) RNA depletion was more severe following than during the appearance of excitatory symptoms. These data indicate that soman poisoning results in metabolic correlates of impaired rather than excessive CNS activation. It is postulated that metabolic disturbances are related to blockade of central cholinergic excitation, and that disruption of functionally integrated synaptic activity forms a critically important aspect of toxication.

Behavioral correlates of neuropathology produced by soman intoxication: M. Z. Mays, J. H. McDonough, Jr., H. E. Modrow, III, C. D. Smith and C. G. McLeod, Jr. United States Army Medical Research Institute of Chemical Defense

Behavioral correlates of neuropathology produced by soman intoxication: M. Z. Mays, J. H. McDonough, Jr., H. E. Modrow, III, C. D. Smith and C. G. McLeod, Jr. United States Army Medical Research Institute of Chemical Defense

Soman and sarin induce a long-lasting naloxone-reversible analgesia in mice

Soman (50 μg/kg) and sarin (120 μg/kg), potent organophosphate anticholinesterase agents, produced an analgesic response in the mouse hotplate latency test. Naloxone antagonized but did not completely reverse the soman- and sarin-induced analgesia, whereas atropine antagonized completely the soman-and sarin-induced analgesia. Soman poisoning did not potentiate morphine-induced analgesia. It was simply an additive response. In survivors of soman (287 μg/kg) poisoning, the analgesia was more pronounced and was still apparent 96 hr after administration. This analgesia was completely antagonized by naloxone. Similar results were found in survivors of sarin (510 μg/kg) poisoning. The organophosphate-induced analgesia was not due to physical incapacitation as evidenced by performance on the accelerating rotorod. It is suggested that the organophosphate-induced analgesia is due to a combination of an increased concentration of acetylcholine due to inhibition of acetylcholinesterase combined with a reduced destruction of endogenous opioid-like substances due to organophosphate inhibition of proteases.

Ferrocene-carbamate as prophylaxis against soman poisoning

The effect of a carbamate derivative of ferrocene as a prophylactic agent toward soman poisoning was studied in mice. A sixfold decrease of the acute toxicity (24-hr LD50) of soman was obtained when the carbamate ( 5.5 mg/kg = 1 30 × LD50 ) was given intraperitoneally 30 min before soman. In this experiment atropine (20 mg/kg ip) was given 10 min before soman as support. The protection was lower when atropine or atropine plus toxogonin were given as therapy (1 min after soman). At these protective doses of the ferrocene-carbamate, a 30% inhibition of blood acetylcholinesterase activity was seen. Like physostigmine, the ferrocene-carbamate inhibited the brain acetylcholinesterase, suggesting that the compound entered the brain tissue.

Stereospecific reactivation by some hagedorn-oximes of acetylcholinesterases from various species including man, inhibited by soman

Reactivation by bispyridinium mono-oximes (Hagedorn-oximes) and some classical oximes (0.03 or 1 mM) was studied in vitro of rat, bovine and human erythrocyte acetylcholinesterase and of electric eel acetylcholinesterase inhibited by soman. Relative reactivating potencies of the oximes are similar for the three inhibited erythrocyte enzymes. In general, Hagedorn-oximes are more potent than the classical oximes. Amont the Hagedorn-oximes, HI-6 is the most potent reactivator for the three inhibited enzymes. Relative reactivating potencies for the inhibited erythrocyte acetylcholinesterases and electric eel acetylcholinesterase, however, clearly differ. Since the reactivation experiments were carried out with racemic soman, a mixture of the two inhibited enzymes may be formed, which may cause additional problems in the comparison of various results. In order to get more detailed information on differences between human erythrocyte and electric eel acetylcholinesterase, reactivation of these enzymes inhibited with the P(−)-isomers of C(+)- and C(−)-soman were studied separately. Reactivation appeared to be dependent on the chirality of the α-carbon atom in the pinacolyl group. HI-6 is by far the most potent reactivator for the human enzyme inhibited by the two P(−)-isomers. It is suggested that electric eel acetylcholinesterase is not a reliable model for in vitro testing of therapeutic potencies of oximes against soman intoxication in mammals. Rate constants of aging of the four acetylcholinesterases inhibited with racemic soman and of the human and eel enzyme inhibited by the P(−)-isomers of C(+)- and C(−)-soman were also determined. The aging of the inhibited rat enzymes proceeds remarkably slowly ( t 1 2 = 21 min ). The rate of aging is not affected by the chirality on the α-carbon atom in the pinacolyl group. Consequences of the present results are discussed in view of extrapolation of reactivation data of a series of reactivators to their relative therapeutic effect, ultimately in man. It is speculated that the more rapid aging of the human inhibited enzyme may hamper oxime-therapy in man more seriously than in rat.

Role of aliesterase in organophosphate poisoning

Various doses of CBDP (2-(2-methylphenoxy)-4 H-1,3,2-benzodioxaphosphorin-2-oxide), a metabolite of tri- o-cresyl phosphate, increased dramatically the acute toxicity of soman (pinacolyl methylphosphonofluoridate) in mice. CBDP (5 mg/kg; iv) reduced the soman LD50 value from 136 μg/kg in control to 6.95 μg/kg. The potentiation of soman toxicity following CBDP pretreatment appeared to be due primarily to inhibition of plasma aliesterase activity. Inhibition of liver aliesterase was not of primary importance in the potentiation of soman toxicity following CBDP pretreatment. In addition pretreatment with ISO-OMPA (tetraisopropyl pyrophosphoramide), a selective inhibitor of pseudocholinesterase, had no effect on the acute toxicity of soman. Similarly pretreatment of mice with pyridostigmine, a quaternary carbamate anticholinesterase which does not inhibit aliesterase, resulted in marked inhibition of diaphragm, plasma, and brain acetylcholinesterase had no effect on the acute toxicity of soman. Plasma aliesterase may be a depot for soman poisoning. The acute toxicity of soman by the ip, sc, and iv routes of administration was reduced following pretreatment of mice with phenobarbital (100 mg/kg) for 4 days. The reduced toxicity of soman following phenobarbital pretreatment was due to induction of liver aliesterase activity which subsequently resulted in an increase in plasma aliesterase activity. Thus more soman was probably bound to plasma aliesterase activity resulting in a reduction in acute toxicity of soman. Conversely pretreatment of mice with pentobarbital (70 mg/kg; ip) increased the toxicity of soman. This was probably the result of inhibition of plasma aliesterase by pentobarbital pretreatment combined with the central respiratory depression following pentobarbital administration. Following pentobarbital pretreatment soman inhibition of brain acetylcholinesterase was increased suggesting that plasma aliesterase inhibition alters the distribution of free soman in vivo. In summary, in mice plasma aliesterase appears to be an extremely important detoxification route for soman in vivo.

Ferrocene—Carbamate as Prophylaxis against Soman Poisoning

Ferrocene—Carbamate as Prophylaxis against Soman Poisoning

Protection against diisopropylfluorophosphate intoxication by pyridostigmine and physostigmine in combination with atropine and mecamylamine.

Atropine (A), mecamylamine (M), pyridostigmine (Py) and physostigmine (Ph) are pretreatment components of Mix I (A = 0.79, M = 0.79, Py = 0.056 mg/kg) and Mix II (A = 0.79, M = 0.79, Ph = 0.026 mg/kg). They have been successfully used in antagonizing Soman intoxication in experimental animals. Rats were pretreated with either Mix I or Mix II and subsequently exposed to diisopropylfluorphosphate (DFP). Pretreatment with Mix I or Mix II (i.m.) 30 min before DFP (i.v.) protected rats from the lethal effects of DFP. The protective ratios were 2.8 (Mix I) and 6.9 (Mix II). Changes in brain levels of acetylcholine (ACh) were measured to help understand the basis for effectiveness of these pretreatments. In the absence of DFP, pretreatments had no significant (P greater than 0.05) effect on bound or free ACh. Pretreatment did not prevent the DFP-induced rise in bound and free ACh nor the agent-induced physical incapacitation at 30 min post exposure. At 2 h after DFP exposure, rats pretreated with Mix II, but not Mix I, showed significant recovery from signs of physical incapacitation. At 30 min after the administration of 3.3 mg/kg of DFP (i.v.), the levels of free and bound ACh in rats given Mix I or Mix II pretreatment increased above control levels by 705% and 116% and 120% and 43%, respectively. By 2 h after DFP, cerebral ACh levels had changed to 437% and 91% with Mix I pretreatment and 26% and 50% with Mix II pretreatment. These data suggest a correlation between DFP-induced increases in the levels of cerebral ACh, possibly free, and physical incapacitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Examination of the role of central cholinergic mechanisms in the therapeutic effects of HI-6 in organophosphate poisoning.

In atropine-pretreated rats, HI-6 (125 mg/kg i.p.) raised the LD50 of Soman (subcutaneous) 5.7 times. Addition of HI-6 (25 micrograms i.c.v.) failed to enhance this protection further. HI-6 (intraperitoneal) also protected animals from intracerebroventricular Soman. HI-6, administered intracerebroventricularly either alone or in combination with intraperitoneal HI-6, failed to increase protection, nor did it reactivate Soman-inhibited acetylcholinesterase (AChE) in several brain areas. HI-6 (125 or 62.5 mg/kg i.p.) protected rats from Sarin lethality, but only the higher dose significantly altered the brain AChE activity. Furthermore, HI-6 (intraperitoneal) failed to block the Soman-induced increase in acetylcholine (ACh) or choline (Ch) levels in any of the brain areas examined. These data indicate that HI-6 is a very beneficial therapy against Soman, but that no definitive central anticholinergic activity of the compound could be found to explain its protective effects. It is possible that HI-6 acts by noncholinergic central mechanisms, or that it produces its beneficial effects outside the CNS. Furthermore, brain AChE activity does not appear to be indicative of protective effects of this oxime. ACh or Ch levels in this study were not good parameters to predict the outcome of Soman poisoning.

Modification of rat brain 5-hydroxytryptamine metabolism by sublethal doses of organophosphate agents.

The early and late effects of sublethal doses of two organophosphate agents (paraoxon and soman) on 5-hydroxytryptamine (5-HT) metabolism were investigated in several rat brain areas. Parallel determinations of acetylcholinesterase (AcChE) inhibition were performed. An increase in 5-HT level was observed during the first phase of soman intoxication and a rise in 5-hydroxyindol acetic acid (5-HIAA) appeared in the early and late effects of both anticholinesterase agents with a predominant action in the striatum. These data suggested that paraoxon and soman induce a long-lasting increase in 5-HT turnover. This action cannot be related neither to the AcChE inhibition nor to the acetylcholine level.

HI-6, an oxime which is an effective antidote of soman poisoning: A structure-activity study

In contrast to other organophosphates, soman poisoning is resistant to atropine (AT) + oxime therapy. However, new bispyridinium-type oximes + AT are effective antidotes of soman poisoning. In structure-activity studies, T 4925 (1,1′-[oxybis(methylene)]bispyridinium dichloride) had an LD 50 of 178 mg/kg and HS-14 (1-[[[pyridinio]methoxy]methyl]-2[(hydroxyiminio)methyl]pyridinium dichloride) had an LD 50 of 130 mg/kg. DL-10 (1-[[[3-(aminocarbonyl)pyridinio]methoxy]methyl]pyridinium dichloride) and DL-11 (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]pyridinium dichloride) had LD 50's of 326 and 715 mg/kg, respectively, whereas HS-6 (Reg. No. 22625-23-6) and HI-6 (Reg. No. 34433-31-3) had LD 50s of 316 and 514 mg/kg (ip), respectively. T 4925, HS-14, DL-10, and DL-11 at an LD 1 dose + AT (17.4 mg/kg) were relatively ineffective against soman (540 μg/kg; sc) compared to HI-6 and HS-6. Prophylactic ED 50s for HI-6 and HS-6 vs soman were 17 and 110 mg/kg, producing safety ratios of 30 and 2.9, respectively. The therapeutic ED 50 for HI-6 was 20 mg/kg. Brain cholinesterase (ChE) in mice surviving soman (540 μg/kg; sc) + HI-6 (94 mg/kg) + AT was 0% of control activity at 1 and 2 hr, 5% at 24 hr, and 15% 48 hr later. Mice which died postsoman (540 μg/kg; sc) had 20% brain ChE activity. These results show that HI-6 was one of the least toxic and most efficacious compounds studied and suggest brain ChE inhibition was not the primary lesion in soman poisoning.

HI-6: Reactivation of central and peripheral acetylcholinesterase following inhibition by soman, sarin and tabun in vivo in the rat

HI-6, ([[[(4-aminocarbonyl)pyridino]methoxy]methyl]-2-[(hydroxyimino)methyl]-pyridinium dichloride), is an oxime which, when combined with atropine, is an extremely effective therapy against organophosphate poisoning. It was found that, following soman (287 μg/kg) poisoning, HI-6 reactivated acetylcholinesterase in the diaphragm and intercostal muscles but not in the brain. At a lower dose of soman (110 μg/kg), HI-6 reactivated acetylcholinesterase in the brain. HI-6 reactivated sarin-inhibited acetylcholinesterase in the brain and in the respiratory musculature but did not reactivate tabun-inhibited acetylcholinesterase. It was also found that soman produced a differential inhibition of diaphragm and intercostal muscle acetylcholinesterase in vivo, whereas the in vitro I 50 for soman was the same in both areas. HI-6 was capable of reactivating soman-inhibited acetylcholinesterase when administered up to 30 min post-soman, indicating that the rate of aging of the soman-acetylcholinesterase complex is slower than previously reported. The above results suggest that, in severe soman poisoning, the primary lesion occurs in peripheral acetylcholinesterase in the respiratory musculature (specifically the diaphragm).

Effect of fasting on the acute toxicity of HI-6 and its efficacy in soman poisoned mice

In rodents HI-6 is a very effective antidote of soman poisoning. After fasting, the IP LD 50value of HI-6 decreased from 660 mg/kg to 550 mg/kg. Fasting had no significant effect on the IV LD 50of HI-6. In fasted animals the ED 50for HI-6 (plus atropine) in soman toxicity decreased from 47.5 mg/kg to 14.8 mg/kg. Investigators should be aware of the nutritional status of the animals when comparing data between various laboratories.

Effect of Fasting on the Acute Toxicity of HI-6 and its Efficacy in Soman Poisoned Mice

Effect of Fasting on the Acute Toxicity of HI-6 and its Efficacy in Soman Poisoned Mice

The inhibition and protection of cholinesterase by physostigmine and pyridostigmine against soman poisoning in vivo

It has been shown that some reversible cholinesterase (ChE) inhibitors as physostigmine and pyridostigmine are prophylactically effective in organophosphate poisoning. The inhibition and protection of ChE against Soman poisoning with the above mentioned drugs was investigated in mice. (1) Physostigmine and pyridostigmine significantly inhibited the ChE in whole blood in vivo and their inhibitory potencies with equitoxic doses were approximately equal (1/5 LD 50 about 30%; 1/2 LD 50 about 45% respectively). Physostigmine also significantly inhibited brain ChE and its potency was slightly weaker than that in blood; but pyridostigmine only slightly inhibited brain ChE (17%) with large dose (1/2 LD 50). The extent of inhibition was in parallel with the dosage of the drugs used. (2) Physostigmine had definite protection in the blood and brain ChE against Soman poisoning. The extent of protection was in parallel with the dosage used. The protection of blood ChE by pyridostigmine was weaker than that by physostigmine. There was no protection of brain ChE by pyridostigmine. (3) The inhibitory potency of equitoxic doses of physostigmine and pyridostigmine in the ChE of diaphragm muscle was equal too (1/2 LD 50 about 45%), and the protective effect of physostigmine was still greater than that of pyridostigmine in Soman poisoning. (4) The time course of blood ChE inhibition by physostigmine in vivo was of short duration. While 30 minutes after administration of physostigmine, the ChE activity gradually recovered and it returned to normal level after 4 hours. The blood ChE inhibition by pyridostigmine reached a peak level after 2 hours, and the ChE activity slowly increased after 4 hours, but there was 30% of ChE activity still inhibited after 8 hours. Physostigmine and pyridostigmine, the reversible ChE inhibitors with carbamate structure, have definite ChE protection against Soman poisoning. The prophylactic efficacy was obviously correlated with their ChE protective potency. Evaluating physostigmine and pyridostigmine based on their efficacy, toxicity, adverse effects, duration, availability and stability, we recommend that pyridostigmine is the drug of choice in the prophylaxis against nerve gas poisoning.

Toxicology and pharmacology of bispyridinium oximes insight into the mechanism of action vs Soman poisoning in vivo

HI-6 was the least toxic and the most efficacious oxime examined against Soman poisoning with a high safety ratio between 26-30. Reactivation of peripheral acetylcholinesterase following Soman poisoning was more important in the beneficial therapeutic action of HI-6 than reactivation of central acetylcholinesterase. HI-6 reactivated Sarin-inhibited but not Tabun-inhibited acetylcholinesterase both peripherally and centrally. HI-6 passes the blood brain barrier as evidenced by its reactivation centrally of Sarin-inhibited acetylcholinesterase. Soman-inhibited enzyme was not aged in vivo by 30 min. In vivo diaphragm acetylcholinesterase was inhibited to a greater extent by Soman, Sarin and Tabun than intercostal muscle acetylcholinesterase. In vitro diaphragm and intercostal muscle acetylcholinesterase had similar IC50 values for Soman. HI-6 has antimuscarinic and antinicotinic activity in addition to its previously reported ganglion blocking activity (Lundy and Tremblay, 1979). These additional pharmacological actions of HI-6 may play a role in the therapeutic action of HI-6 (at the higher concentrations). The results suggest that peripheral acetylcholinesterase in the rat diaphragm is the primary lesion in Soman poisoning. The beneficial action of HI-6 in rats versus Soman poisoning is due to reactivation of diaphragm acetylcholinesterase.

The treatment of soman poisoning and its perspectives

Soman is a highly, toxic organophosphorus chemical warfare nerve agent which is characterizee by (1) extremely rapid ageing of the phosphonylated enzyme, (2) poor reactivation of inhibited AChE due to a steric factor, (3) pronounced CNS effects and (4) tentative direct toxic biochemical effects. By studies of Soman and its thiocholine-like analog (which yield the same type of phosphonylated enzyme), it has been established that (1) the steric factor is at least as responsible as ageing in the failure of oximes to reactivate effectively AChE inhibited by Soman, (2) that its dealkylation is catalyzed by the anionic site of the enzyme, and (3) that the velocity of reactivation and ageing of AChE is dependent on the orientation of the phosphonyl group at the enzyme surface. It has been found that PiMeP-Cl (O-pinacolyl methylphosphonochloridate) may serve as a good model in the evaluation of Soman toxicity and in the selection of adequate oximes in the treatment of its poisoning. The opposite effects of TMB-4 and HI-6, as group representatives, on PiMeP-Cl toxicity in mice (strong, potentiation by TMB-4 and anatagonism by HI-6) were mainly ascribed to the rates of decomposition of their corresponding O-pinacolyl methylphosphonylated products formed in vivo. They are considered to be slow with potentiators and instantaneous with antagonists, respectively. This assumption was confirmed by the finding that the most powerful oximes in Soman poisoned mice were HI-6, HGG-42 and BDB-27, which, contrary to TMB-4, possess an oxime group in position 2 and the CH 2−O−CH 2 linking chain. The remarkable influence of diazepam and sodium n-dipropylacetate on the survival time in Soman poisoned rats treated by atropine and bis-pyridinium oximes points to their antagonistic action at the biochemical level, (decrease of elevated cGMP in CNS), not possessed by atropine. Essential antidotes in experimental treatment of Soman poisoning today are the powerful reactivators of Soman-inhibited AChE ( e.g. HI-6, HGG-42 and BDB-27) and atropine. The treatment may be further improved by the use of symptomatic agents capable of counteracting biochemical changes in Soman poisoning not antagonized by atropine ( e.g. diazepam(, and theoretically for now, by retardation of ageing and by overcoming steric disturbances.

Analysis of oxime-induced neuromuscular recovery in guinea pig, rat and man following soman poisoning in vitro

Two bispyridinium oximes HS6 and HI6 were tested in vitro for their ability to restore neuromuscular function in soman-poisoned tissue, using diaphragm and intercostal muscle of the rat and guinea pig and intercostal muscle of man. It was found that the oxime-mediated recovery of function in both tissues of the rat and guinea pig was composed of direct oxime actions, AChE reactivation and adaptation. In human intercostal muscle, however, only adaptation was observed. These findings might suggest that HS6 and HI6 may have only limited value in the treatment of soman poisoning in man. However, recovery of function in rodent tissues was consistently greater in the diaphragm than in the intercostal muscle and, since human diaphragm tissue was not included in this study the therapeutic efficacy of these oximes in this tissue remains unknown.

The treatment of soman poisoning and its perspectives

The treatment of soman poisoning and its perspectives

Circadian susceptibility to soman poisoning

Circadian susceptibility to soman poisoning