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Toxicology Mechanisms and Methods Sep 2012Misuse of various chemicals, such as chemical warfare agents, industrial chemicals or pesticides during warfare or terrorists attacks requires adequate protection. Thus,...
Misuse of various chemicals, such as chemical warfare agents, industrial chemicals or pesticides during warfare or terrorists attacks requires adequate protection. Thus, development and evaluation of novel decontamination dispositives and techniques are needed. In this study, in vitro permeation and decontamination of a potentially hazardous compound paraoxon, an active metabolite of organophosphorus pesticide parathion, was investigated. Skin permeation and decontamination experiments were carried out in modified Franz diffusion cells. Pig skin was used as a human skin model. Commercially produced detergent-based washing solutions FloraFree(™) and ArgosTM were used as decontamination means. The experiments were done under "warm", "cold", "dry" and "wet" skin conditions in order to determine an effect of various physical conditions on skin permeation of paraoxon and on a subsequent decontamination process. There was no significant difference in skin permeation of paraoxon under warm, cold and dry conditions, whereas wet conditions provided significantly higher permeation rates. In the selected conditions, decontamination treatments performed 1 h after a skin exposure did not decrease the agent volume that permeated through the skin. An exception were wet skin conditions with non-significant decontamination efficacy 18 and 28% for the FloraFree(™) and Argos(™) treatment, respectively. In contrast, the skin permeation of paraoxon under warm, cold and dry conditions increased up to 60-290% following decontamination compared to non-decontaminated controls. This has previously been described as a skin wash-in effect.
Topics: Animals; Chemical Phenomena; Decontamination; Detergents; Diffusion Chambers, Culture; Female; Humans; In Vitro Techniques; Paraoxon; Permeability; Pesticides; Skin; Skin Absorption; Sus scrofa; Time Factors
PubMed: 22519880
DOI: 10.3109/15376516.2012.686535 -
Applied Biochemistry and Biotechnology May 2015Rapid detection of organophosphorous (OP) compounds such as paraoxon would allow taking immediate decision on efficient decontamination procedures and could prevent...
Rapid detection of organophosphorous (OP) compounds such as paraoxon would allow taking immediate decision on efficient decontamination procedures and could prevent further damage and potential casualties. In the present study, a biosensor based on nanomagnet-silica core-shell conjugated to organophosphorous hydrolase (OPH) enzyme was designed for detection of paraoxon. Coumarin1, a competitive inhibitor of the OPH enzyme, was used as a fluorescence-generating molecule. Upon excitation of cumarin1 located at the active site of the enzyme, i.e., OPH, the emitted radiations were intensified due to the mirroring effect of the nanomagnet-silica core-shell conjugated to the enzyme. In presence of paraoxon and consequent competition with the fluorophore in occupying enzyme's active site, a significant reduction in emitted radiations was observed. This reduction was proportional to paraoxon concentration in the sample. The method worked in the 10- to 250-nM concentration range had a low standard deviation (with a coefficient of variation (CV) of 6-10%), and the detection limit was as low as 5 × 10(-6) μM.
Topics: Aryldialkylphosphatase; Bacterial Proteins; Biosensing Techniques; Coumarins; Magnetite Nanoparticles; Paraoxon; Pseudomonas; Silicon Dioxide
PubMed: 25825249
DOI: 10.1007/s12010-015-1579-1 -
Journal of Hazardous Materials Aug 2012Molecularly imprinted polymers were grafted on the surface of multiwalled carbon nanotubes (MWCNT) using the hydrolysis product of paraoxon 4-nitrophenol as template,...
Molecularly imprinted polymers were grafted on the surface of multiwalled carbon nanotubes (MWCNT) using the hydrolysis product of paraoxon 4-nitrophenol as template, 4-vinyl pyridine (4-VPy) as the functional monomer and divinylbenzen (DVB) as the crosslinker. The binding experiments of 4-nitrophenol indicated that the MWCNT based molecularly imprinted polymers (MWCNT-MIP) have much higher adsorption ability than the MWCNT based non-imprinted polymers (MWCNT-NIP). At the same time we found that the adsorption of 4-nitrophenol can help to increase the hydrolytic rate of paraoxon, which indicates that there is an obvious catalyzing effect on the hydrolysis of paraoxon for this kind of materials. Furthermore, the 4-nitrophenol left in the paraoxon hydrolysis medium is only 0.01056 mM for MWCNT-MIP in the catalytic experiment of paraoxon we made (the initial concentration of paraoxon is 0.5 mM and MWCNT-MIP is 4 mg), which indicates that this kind of MWCNT based imprinted polymers can not only catalyze the hydrolysis of paraoxon but also eliminate the poisonous organism product 4-nitrophenol.
Topics: Adsorption; Catalysis; Hydrolysis; Insecticides; Molecular Imprinting; Nanotubes, Carbon; Nitrophenols; Paraoxon; Polymers; Water Pollutants, Chemical; Water Pollution
PubMed: 22652321
DOI: 10.1016/j.jhazmat.2012.05.041 -
Sensors (Basel, Switzerland) 2010Porphyrins are a family of highly conjugated molecules that strongly absorb visible light and fluoresce intensely. These molecules are sensitive to changes in their...
Porphyrins are a family of highly conjugated molecules that strongly absorb visible light and fluoresce intensely. These molecules are sensitive to changes in their immediate environment and have been widely described for optical detection applications. Surfactant-templated organosilicate materials have been described for the semi-selective adsorption of small molecule contaminants. These structures offer high surface areas and large pore volumes within an organized framework. The organic bridging groups in the materials can be altered to provide varied binding characteristics. This effort seeks to utilize the tunable binding selectivity, high surface area, and low materials density of these highly ordered pore networks and to combine them with the unique spectrophotometric properties of porphyrins. In the porphyrin-embedded materials (PEMs), the organosilicate scaffold stabilizes the porphyrin and facilitates optimal orientation of porphyrin and target. The materials can be stored under ambient conditions and offer exceptional shelf-life. Here, we report on the design of PEMs with specificity for organophosphates and compounds of similar structure.
Topics: Fluorescent Dyes; Organosilicon Compounds; Paraoxon; Porphyrins; Silicates; Spectrometry, Fluorescence; Surface-Active Agents
PubMed: 22294928
DOI: 10.3390/s100302315 -
Chemical Research in Toxicology Jan 2011In this work kinetic data were obtained for different paraoxon concentrations incubated with chicken serum and the soluble fraction of chicken peripheral nerve. A...
In this work kinetic data were obtained for different paraoxon concentrations incubated with chicken serum and the soluble fraction of chicken peripheral nerve. A kinetic model equation was deduced by assuming a multienzymatic system with three different simultaneously occurring molecular phenomena: (1) inhibition; (2) simultaneous spontaneous reactivation; (3) "ongoing" inhibition (inhibition during the substrate reaction). A three-dimensional fit of the model was applied to analyze the experimental data versus the concentration of the inhibitor and the preincubation time in an inhibition experiment. The best-fitting model in the soluble fraction of chicken peripheral nerve was compatible with a resistant component (22%) and with two sensitive enzymatic entities (37 and 41%). The corresponding second-order rate constants of inhibition (k(i) = 1.8 × 10(-3) and 5.1 × 10(-3) nM(-1) min(-1), respectively) and the spontaneous reactivation constants (k(r) = 0.428 and 0.011 min(-1), respectively) were estimated. The best-fitting model in chicken serum was compatible with a resistant component (5.6%) and with two sensitive enzymatic entities (22.1 and 72.3%). The corresponding second-order rate constants of inhibition (k(i) = 5.8 × 10(-2) and 2.0 × 10(-3) nM(-1) min(-1), respectively) and the spontaneous reactivation constants (k(r) = 0.0044 and 0.0091 min(-1), respectively) were estimated. These parameters were similar to those observed in spontaneous reactivation experiments with preinhibited paraoxon samples. The consistency of the results of all the experiments is considered an internal validation of the methodology. The results are also consistent with a significant ongoing inhibition. The proportion of enzymatic components shown in this work by the inhibition and reactivation of paraoxon is similar to that previously observed in inhibition experiments with mipafox in both tissues, demonstrating that this kinetic approach provides consistent results in complex enzymatic systems. The high sensitivity (at nanomolar concentrations) of these esterases suggests that they may either play a role in toxicity in low-level long-term exposure of organophosphate compounds or have a protective effect related with the spontaneous reactivation.
Topics: Animals; Carboxylic Ester Hydrolases; Chickens; Enzyme Inhibitors; Kinetics; Models, Chemical; Organophosphorus Compounds; Paraoxon
PubMed: 21155548
DOI: 10.1021/tx100346c -
Bioorganic & Medicinal Chemistry Sep 2008Acetylcholinesterase reactivators are crucial antidotes for the treatment of organophosphate intoxication. Eighteen monoquaternary reactivators of acetylcholinesterase...
Acetylcholinesterase reactivators are crucial antidotes for the treatment of organophosphate intoxication. Eighteen monoquaternary reactivators of acetylcholinesterase with modified side chain were developed in an effort to extend the properties of pralidoxime. The known reactivators (pralidoxime, HI-6, obidoxime, trimedoxime, methoxime) and the prepared compounds were tested in vitro on a model of tabun- and paraoxon-inhibited AChE. Monoquaternary reactivators were not able to exceed the best known compounds for tabun poisoning, but some of them did show reactivation better or comparable with pralidoxime for paraoxon poisoning. However, extensive differences were found by a SAR study for various side chains on the non-oxime part of the reactivator molecule.
Topics: Acetylcholinesterase; Animals; Brain; Cholinesterase Inhibitors; Dose-Response Relationship, Drug; Drug Design; Drug Evaluation, Preclinical; Enzyme Activation; Enzyme Activators; Models, Biological; Molecular Structure; Organophosphates; Paraoxon; Pyridinium Compounds; Rats; Stereoisomerism; Structure-Activity Relationship
PubMed: 18676153
DOI: 10.1016/j.bmc.2008.07.036 -
General Pharmacology 19881. Paraoxon (10 microM for 20 min) induced a desensitization of the taenia caecum of the guinea-pig for contractions produced by a number of cholinomimetics. 2....
1. Paraoxon (10 microM for 20 min) induced a desensitization of the taenia caecum of the guinea-pig for contractions produced by a number of cholinomimetics. 2. Tetrodotoxin (0.3 microM) reversed the desensitization suggesting involvement of Na+ channels.
Topics: Animals; Carbachol; Guinea Pigs; Ion Channels; Paraoxon; Pilocarpine; Pyrrolidines; Sodium; Tetrodotoxin
PubMed: 2457538
DOI: 10.1016/0306-3623(88)90168-1 -
Toxicology and Applied Pharmacology Jan 1996These experiments examined the changes in acetylcholinesterase (AChE) during tolerance development in rats exposed to paraoxon, an irreversible inhibitor of AChE. Rats... (Comparative Study)
Comparative Study
These experiments examined the changes in acetylcholinesterase (AChE) during tolerance development in rats exposed to paraoxon, an irreversible inhibitor of AChE. Rats were injected sc for 20 days with 0.09, 0.12, or 0.19 mg/kg of paraoxon. Tolerance to the clinical signs of paraoxon toxicity developed rapidly. The hypothesis was tested that changes in the kinetics of reactivity of AChE with its substrate acetylcholine (ACh) and the inhibitor paraoxon contribute to the observed tolerance. The kinetic constants Vmax and Km were determined by Lineweaver-Burk transformations. The affinity (Kd), phosphorylation (kp) and the bimolecular rate (ki) constants were established from slopes and standard deviations of inhibition curves. Acetylcholinesterase properties of brain and diaphragm from controls and paraoxon-tolerant rats were compared. In controls, Km, determining the affinity of AChE for ACh, was 0.063 x 10(-3) M and 0.072 x 10(-3) M for diaphragm and brain, respectively. In paraoxon-tolerant rats, the affinity of AChE for ACh increased since the Km for diaphragm was reduced to 0.047 x 10(-3) M and the Km for brain to 0.057 x 10(-3) M. This decrease was seen with all paraoxon concentrations and was significantly different from controls after the fifth day of treatment. Small, significant increases of IC50 values for paraoxon were observed in diaphragm (from 27.30 to 45.14 nM) and in brain (from 13.67 to 15.38 nM). In brain, a 20-day treatment with paraoxon caused a fivefold decrease in the dissociation constant (Kd) from 1.56 to 0.268 microM and a threefold decrease in the phosphorylation constant (kp) from 4.72 to 1.52 min-1. The observed changes in diaphragm were smaller and not significant. The increase in affinity to ACh gives an advantage to tolerant rats, because the remaining reduced amount of AChE can hydrolyze ACh more efficiently, regardless of the change in sensitivity to the inhibitor. The observed changes may be the result of structural changes of AChE or the result of altered levels of preexisting isozymes of AChE.
Topics: Acetylcholinesterase; Analysis of Variance; Animals; Brain; Butyrylcholinesterase; Cholinesterase Inhibitors; Diaphragm; Injections, Subcutaneous; Insecticides; Isoenzymes; Lethal Dose 50; Male; Paraoxon; Rats; Rats, Sprague-Dawley
PubMed: 8560475
DOI: 10.1006/taap.1996.0003 -
The Journal of Physical Chemistry. B Dec 2011The bacterial enzyme organophosphorus hydrolase (OPH) exhibits both catalytic and substrate promiscuity. It hydrolyzes bonds in a variety of phosphotriester (P-O),...
The bacterial enzyme organophosphorus hydrolase (OPH) exhibits both catalytic and substrate promiscuity. It hydrolyzes bonds in a variety of phosphotriester (P-O), phosphonothioate (P-S), phosphofluoridate (P-F), and phosphonocyanate (F-CN) compounds. However, its catalytic efficiency varies markedly for different substrates, limiting the broad-range application of OPH as catalyst in the bioremediation of pesticides and chemical war agents. In the present study, pK(a) calculations and multiple explicit-solvent molecular dynamics (MD) simulations were performed to characterize and contrast the structural dynamics of OPH bound to two substrates hydrolyzed with very distinct catalytic efficiencies: the nerve agent soman (O-pinacolylmethylphosphonofluoridate) and the pesticide paraoxon (diethyl p-nitrophenyl phosphate). pK(a) calculations for the substrate-bound and unbound enzyme showed a significant pK(a) shift from standard values (ΔpK(a) = ±3 units) for residues His254 and Arg275. MD simulations of protonated His254 revealed a dynamic hydrogen bond network connecting the catalytic residue Asp301 via His254 to Asp232, Asp233, Arg275, and Asp235, and is consistent with a previously postulated proton relay mechanism to ferry protons away from the active site with substrates that do not require activation of the leaving group. Hydrogen bonds between Asp301 and His254 were persistent in the OPH-paraoxon complex but not in the OPH-soman one, suggesting a potential role for such interaction in the more efficient hydrolysis of paraoxon over soman by OPH. These results are in line with previous mutational studies of residue His254, which led to an increase of the catalytic efficiency of OPH over soman yet decreased its efficiency for paraoxon. In addition, comparative analysis of the molecular trajectories for OPH bound to soman and paraoxon suggests that binding of the latter facilitates the conformational transition of OPH from the open to the closed substate promoting a tighter binding of paraoxon.
Topics: Aryldialkylphosphatase; Bacteria; Hydrogen Bonding; Kinetics; Molecular Dynamics Simulation; Mutation; Paraoxon; Protein Binding; Soman
PubMed: 22098575
DOI: 10.1021/jp208787g -
Toxicological Sciences : An Official... Aug 2004The primary mechanism of action for organophosphorus (OP) insecticides, like chlorpyrifos and parathion, is to inhibit acetylcholinesterase (AChE) by their oxygenated... (Comparative Study)
Comparative Study
The primary mechanism of action for organophosphorus (OP) insecticides, like chlorpyrifos and parathion, is to inhibit acetylcholinesterase (AChE) by their oxygenated metabolites (oxons), due to the phosphorylation of the serine hydroxyl group located in the active site of the molecule. The rate of phosphorylation is described by the bimolecular inhibitory rate constant (k(i)), which has been used for quantification of OP inhibitory capacity. It has been proposed that a peripheral binding site exists on the AChE molecule, which, when occupied, reduces the capacity of additional oxon molecules to phosphorylate the active site. The aim of this study was to evaluate the interaction of chlorpyrifos oxon (CPO) and paraoxon (PO) with rat brain AChE to assess the dynamics of AChE inhibition and the potential role of a peripheral binding site. The k(i) values for AChE inhibition determined at oxon concentrations of 1-100 nM were 0.206 +/- 0.018 and 0.0216 nM(-1)h(-1) for CPO and PO, respectively. The spontaneous reactivation rates of the inhibited AChE for CPO and PO were 0.084-0.087 (two determinations) and 0.091 +/- 0.023 h(-1), respectively. In contrast, the k(i) values estimated at a low oxon concentration (1 pM) were approximately 1,000- and 10,000-fold higher than those determined at high CPO and PO concentrations, respectively. At low concentrations, the k(i) estimates were approximately similar for both CPO and PO (150-180 [two determinations] and 300 +/- 180 nM(-1)h(-1), respectively). This implies that, at low concentrations, both oxons exhibited similar inhibitory potency in contrast to the marked difference exhibited at higher concentrations. These results support the potential importance of a secondary peripheral binding site associated with AChE kinetics, particularly at low, environmentally relevant concentrations.
Topics: Acetylcholinesterase; Algorithms; Animals; Binding Sites; Brain; Chlorpyrifos; Cholinesterase Inhibitors; Dose-Response Relationship, Drug; In Vitro Techniques; Kinetics; Male; Paraoxon; Rats; Rats, Sprague-Dawley; Structure-Activity Relationship
PubMed: 15141101
DOI: 10.1093/toxsci/kfh163