197,345 research outputs found
Directed evolution of phosphotriesterase: towards the efficient detoxification of sarin and soman
No full textDirected evolution studies were done with PTE for the enhancement of hydrolysis of both sarin and soman analogs. Particular attention was focused on the toxic SpRc and SpSc isomers of the soman analog, and the Sp isomer of the sarin analog. Double substitution libraries yielded several mutants that had enhanced activity for the substrates. Among them was the double mutant, H257Y-L303T, which displayed a 462-fold increase in activity for hydrolysis of the most toxic SpSc isomer of the GD analog in comparison to the wild type. Several other mutants such as the triple mutants H254R-H257A-L303T and H254R-H257S-L303T had enhancements of between 150- and 200-fold, and had also displayed a different order of stereoselectivity relative to the wild type. For these mutants, the order of preferential hydrolysis was such that the SpRc isomer was preferentially hydrolyzed first. In contrast, the order of preferential hydrolysis for the wild type was that the RpRc was hydrolyzed first, followed by the RpSc, SpRc, and then the SpSc isomer. The reversal of stereoselective preference was also seen with the double substitution library members for hydrolysis of the sarin analog isomers. However, there were no significant improvements for sarin analog hydrolysis in these libraries. Among the best mutants obtained were H254G-H257W, H254G-H257R, and H257Y, all of which had catalytic efficiencies on the order of 106 M-1 s-1 for hydrolysis of the Sp isomer.
The toxicity for analogs of sarin, soman, and VX was evaluated using Hydra
attenuata as a model organism. The toxicity of each compound was assessed quantitatively by measuring the minimal effective concentration within 92 h in H. attenuata. There was a positive correlation between the molecular hydrophobicity of the compound and its ability to cause toxicity. Results from this study indicate the potential for application of this assay in the field of organophosphate nerve agent detection, as well as for the prediction of toxicity of structurally similar organophosphate compounds. The minimal effective concentration for two of the VX analogs was 2 orders of magnitude more toxic than the analog for soman and four orders of magnitude more toxic than the analog for sarin
Retention of Soman in Rats, Guinea-pigs and Marmosets: Species-dependent Effects of the Soman Simulator, Pinacolyl Dimethylphosphinate (PDP)
No full textAbstract
Whether the temporary retention of intact soman in the rat and its subsequent delivery from tissues into the circulation of the blood is also demonstrable in guinea-pigs and marmosets has been investigated as was whether the soman simulator PDP (pinacolyl dimethylphosphinate) prevented this retention. Electric eel AChE, intravenously injected 1.5 h after an intravenous soman intoxication into anaesthetized, atropinized and artificially ventilated guinea-pigs (150 μg kg−1 soman), marmoset monkeys (100 μg kg−1 soman) and rats (330 and 172.5 μg kg−1 soman) lost its activity faster than enzyme injected in non-intoxicated animals. Electric eel AChE incubated in the presence of pectoralis or diaphragm muscle isolated from soman-intoxicated rats, guinea-pigs and marmosets 0.5 or 1.5 h after the intoxication, was progressively inhibited, indicating that those muscles still delivered soman into the incubation medium. In rats, PDP (6.4 mg kg−1 i.v.) pretreatment was effective in preventing inhibition of intravenously injected electric eel AChE 1.5 h after intoxication with a high dose of soman (330 μg kg−1). But after intoxication with a low dose (172.5 μg kg−1), PDP pretreatment was ineffective in this action, however, it did lead to less soman delivery from muscle tissue isolated 30 min following the 172.5 μg kg−1 soman intoxication, suggesting that there was less soman in the tissue. In PDP (6.4 mg kg−1 i.v.)-pretreated marmosets (100 μg kg−1 soman) and guinea-pigs (150 μg kg−1 soman), to the contrary, the trend was for the injected AChE to be more inhibited, whereas only slightly less soman was delivered from isolated muscle tissue. It is suggested that after PDP treatment to rats the elimination of soman from the blood circulation is faster than in marmosets and guinea-pigs.</jats:p
Naloxone Antagonizes Soman-induced Central Respiratory Depression in Rats
No full text© 2016 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society) The influence of naloxone on respiration impaired by the highly toxic organophosphate nerve agent soman in anaesthetized rats was investigated. Soman, administered in a dose that was ineffective in blocking the electrically induced contractions of the phrenic nerve-diaphragm preparation in situ, induced a complete block of the spontaneous respiratory movements of the diaphragm, indicating the domination of central over the peripheral effects. Naloxone dose-dependently antagonized the soman-induced respiratory blockade. Atropine, at a dose that was per se ineffective in counteracting soman-induced respiratory depression, potentiated the protective effects of naloxone and completely restored respiration. Naloxone remained completely ineffective in antagonizing respiratory depression induced by the muscarinic receptor agonist the oxotremorine. It is assumed that naloxone antagonizes soman-induced respiratory inhibition by blocking endogenous opioidergic respiratory control pathways that are independent of the stimulation of muscarinic receptors
Inhalation Apparatus for Generating Sarin and Soman Toxic Vapors
No full textThe developed inhalation system is a dynamic and whole-body exposure model designated for generating sarin or soman vapors. It consists of an evaporating apparatus, an inhalation chamber and a carbon filter. The inhalation chamber is made of stainless steel and its total volume is 36 l. The concentration of organophosphorus compound depends on airflow through the chamber, syringe volume of the dosing pump and dosing speed. For determination of organophosphorus compound (OPC) concentration, a modification of Ellman method is used. At generating of vapors in the inhalation chamber the means of the yield were 61.4 ± 6.6 % for sarin and 35.8 ± 3.5 % for soman. The better yield for sarin than for soman, because of the higher volatility of sarin in comparison with soman was achieved. The stable concentration of the OPC for several hours could be maintained in the inhalation chamber when only relatively small amount of the OPC is used. Using the developed inhalation system LCt50 for sarin and for soman in rats was determined. At 1 h exposure the LCt50 values were 4.72 mg.h-1.m-3 for sarin and 4.81 mg.h-1.m-3 for soman. The results presented show that the inhalation chamber successfully fulfils the role of instrument for inhalation intoxication of small laboratory animals with highly toxic OPC
Prophylactic and therapeutic efficacy of the soman-simulator, pinacolyl dimethylphosphinate
No full textAbstract
Atropinized rats, intoxicated with 6 or 8 × LD50 soman and subsequently treated with the oxime HI-6 died several hours after intoxication. Oral or intravenous administration of the soman-simulator, pinacolyl dimethylphosphinate (PDP), given at progressively increasing time intervals before soman, appeared to be very active in preventing death and secondary failure of neuromuscular transmission that followed HI-6-induced recovery. Therapeutically, PDP was only effective when given immediately after soman intoxication and oxime treatment. In animals that received no treatment otherwise, intravenous administration of PDP 10 min before intoxication with 1 × LD50 soman did not enhance lethality.</jats:p
Administration of (−)-phenserine prior to but not after soman protects against soman-induced mortality.
No full text<p>Rats were administered (−)-phenserine, posiphen or saline 4 hr (A), or 30 min (B) prior to or 5 min (C) or 30 min (D) after soman. In the 4 hr pretreatment groups of animals, 12 rats died in the posiphen group and 11 rats died in the control group. There were no deaths in the (−)-phenserine group. In the 30 min pretreatment groups of animals, 2 animals died in the (−)-phenserine group. The bar represents the percent of surviving rats 24 hr after soman exposure calculated as: number of surviving rats 24 hr after soman/total number of rats ×100. n = 17–20. *p<0.026 <i>vs</i> saline/soman by Fisher exact test.</p
Effectiveness of pyridostigmine in reversing neuromuscular blockade produced by soman
No full textAbstract
The effects of pyridostigmine pretreatment on the neuromuscular blockade produced by soman in anaesthetized, atropinized animals have been studied on the soleus and anterior tibialis muscle (rhesus monkeys, cats and rabbits) and the gastrocnemius muscle (guinea-pigs and rats). Pyridostigmine pretreatment produced a complete recovery of neuromuscular function following blockade by soman; the rate of recovery was similar in all the species, suggesting a common mechanism of action. In the absence of pyridostigmine or if pyridostigmine was delayed until after blockade by soman, there was no recovery of neuromuscular function. Detailed studies in the guinea-pig showed that the recovery of neuromuscular function was related to the dose of soman and to the degree of carbamoylation of blood cholinesterase at the time of nerve agent challenge, i.e. to the dose of pyridostigmine and the time interval between the administration of pyridostigmine and soman. It is suggested that the effectiveness of pyridostigmine pretreatment is due to the carbamoylation of a portion of the tissue acetylcholinesterase, which protects it against irreversible inhibition by soman: after poisoning spontaneous decarbamoylation produces sufficient free acetylcholinesterase to restore normal function.</jats:p
Cerebral microvascular effects of nimodipine in combination with soman
No full textNimodipine, a calcium antagonist, has been shown to increase the detoxification of soman. In this study the cerebral microcirculatory effects of nimodipine and the acetylcholinesterase inhibitor soman was studied. Anaesthetised rats were administered nimodipine, 10 mg kg(-1) or vehicle intra-peritoneally, and 1 h later exposed to 45 mu g kg(-1) soman intravenously. The regional blood flows were measured using the microsphere method. Nimodipine and soman markedly increased the cerebral blood flow (CBF) and reduced the vascular resistance. Total CBF increased by 146% after nimodipine and by 105% after soman administration. Combined administration of nimodipine and soman caused additional but not fully additive effects on CBF and vascular resistance, indicating possible different mechanisms of the two agents. A part of the nimodipine induced increased detoxification after AChE-inhibition may be associated with this cerebral vasodilation. (C) 2012 Elsevier B.V. All rights reserved.</p
(-)-Phenserine attenuates soman-induced neuropathology.
No full textOrganophosphorus (OP) nerve agents are deadly chemical weapons that pose an alarming threat to military and civilian populations. The irreversible inhibition of the critical cholinergic degradative enzyme acetylcholinesterase (AChE) by OP nerve agents leads to cholinergic crisis. Resulting excessive synaptic acetylcholine levels leads to status epilepticus that, in turn, results in brain damage. Current countermeasures are only modestly effective in protecting against OP-induced brain damage, supporting interest for evaluation of new ones. (-)-Phenserine is a reversible AChE inhibitor possessing neuroprotective and amyloid precursor protein lowering actions that reached Phase III clinical trials for Alzheimer's Disease where it exhibited a wide safety margin. This compound preferentially enters the CNS and has potential to impede soman binding to the active site of AChE to, thereby, serve in a protective capacity. Herein, we demonstrate that (-)-phenserine protects neurons against soman-induced neuronal cell death in rats when administered either as a pretreatment or post-treatment paradigm, improves motoric movement in soman-exposed animals and reduces mortality when given as a pretreatment. Gene expression analysis, undertaken to elucidate mechanism, showed that (-)-phenserine pretreatment increased select neuroprotective genes and reversed a Homer1 expression elevation induced by soman exposure. These studies suggest that (-)-phenserine warrants further evaluation as an OP nerve agent protective strategy
The Effect of the Calcium Antagonist Nimodipine on the Detoxification of Soman in Anaesthetized Rabbits
No full textAbstract
The effect of nimodipine, a vasoactive calcium antagonist, on the disappearance of soman from blood was studied in anaesthetized rabbits intoxicated with soman (10.8 μg kg−1 i.v.). Blood samples from the left heart ventricle and femoral artery were used to investigate soman detoxification. The concentrations of the soman isomers C + P - and C - P - in blood samples were determined by gas chromatography coupled with high-resolution mass spectrometry.
During the sampling, 15–300 s after soman injection, the soman concentration in control animals decreased from 50 to 0.029 ng mL−1; in animals pre-treated with nimodipine (10 mg kg−1) it decreased from 15 to 0.033 ng mL−1. In animals pre-treated with nimodipine the soman concentration was significantly reduced during the first minute of sampling. No differences were detected between soman concentrations in samples from the heart and femoral artery. Acetylcholinesterase inhibition was also used as an indicator of soman activity; there was no difference between the activity of this enzyme in different peripheral organs of control and nimodipine-treated animals.
Nimodipine reduces the initial concentration of soman in the blood, which might be of significance in the treatment of soman intoxication.</jats:p
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