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James P. O'callaghan - One of the best experts on this subject based on the ideXlab platform.
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Neurotoxic Esterase: not so toxic?
Nature Genetics, 2003Co-Authors: James P. O'callaghanAbstract:An altered form of an Esterase has been implicated in the development of Neurotoxicity after exposure to organophosphates. Mice deficient in this enzyme should be less susceptible to toxicity, but the opposite turns out to be the case.
Rudy J. Richardson - One of the best experts on this subject based on the ideXlab platform.
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SUMMARY
2016Co-Authors: Paul E. Gurba, Rudy J. RichardsonAbstract:Neurotoxic Esterase (NTE), the putative target far organophosphorus-induced delayed axonopathy, has been found in preparations of human placenta. The activity was primarily found in membrane-enriched fractions rather than high-speed supernatant. NTE was solubilized from a mixture of mitochon-drial and microsomal membranes with Triton X-100. The crude and solubilized activities had inhibitor characteristics similar to preparations from avian brain. Because of the similarities to NTE from brain and ready availability, human placenta may be an ideal source for the bulk purification of a human form of the enzyme
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Inhibition of Neurotoxic Esterase in Vitro by Novel Carbamates
Toxicology and Applied Pharmacology, 1997Co-Authors: Joseph C. Randall, Jeffrey L. Ambroso, William C. Groutas, Michael J. Brubaker, Rudy J. RichardsonAbstract:Carbamyl sulfonate (CS) compounds are a novel class of carbamates derived from amino acid methyl esters. They have the general structure RCH(COOCH3)NH(CO)SO-3K+, where R is the sidechain of the parent amino acid. These compounds were developed as active site-directed inhibitors of human leukocyte elastase (HLE). The purpose of this study was to characterize the inhibition of hen brain Neurotoxic Esterase (neuropathy target Esterase, NTE), horse serum butyrylcholinEsterase (BuChE), and bovine erythrocyte acetylcholinEsterase (AChE) by CS analogs derived from the methyl esters of L-ala, D-norval, L-norval, L-phe, L-val, L-norleu, D-met, and L-met. Bimolecular rate constants of inhibition (ki) for NTE ranged from 0.571 for L-ala-CS to 17.7 mM-1 min-1 for L-norleu-CS (10-min I50 values of 123 and 3.92 microM, respectively). Potency against NTE increased with chain length for straight-chain R-groups of L-CS compounds. Unlike HLE, NTE was only weakly stereoselective for CS compound enantiomers. The L-isomers were weaker inhibitors of BuChE than NTE (10-min I50 range of 742 to 35.6 microM). In contrast to the L-enantiomers, the I50 plots of D-met-CS and D-norval-CS were not linear for BuChE, suggesting a possible stereospecific mechanistic shift for inhibition of this enzyme, AChE was not effectively inhibited by any of the CS compounds (I50 values > 750 microM). The specificity and charged nature of CS compounds give these unusual NTE inhibitors potential advantages for mechanistic studies of organophosphorus compound-induced delayed Neurotoxicity (OPIDN) and its protection or potentiation.
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Relative potencies of the four stereoisomers of isomalathion for inhibition of hen brain acetylcholinEsterase and Neurotoxic Esterase in vitro
Toxicology and Applied Pharmacology, 1996Co-Authors: Suree Jianmongkol, Clifford E. Berkman, Charles M. Thompson, Rudy J. RichardsonAbstract:The cholinergic toxicity of malathion is exacerbated by its isomerization product, isomalathion, which inhibits detoxifying carboxylEsterases as well as target acetylcholinEsterase (AChE). Previous work has shown that the four stereoisomers of isomalathion, (1R, 3R), (1R, 3S), (1S, 3R), and (1S, 3S), differ in their inhibitory potencies against either rat brain or electric eel AChE. The present study examined the relative inhibitory potencies of these stereoisomers and the totally racemic mixture (1RS, 3RS) against hen brain AChE and Neurotoxic Esterase (NTE) to provide new data on stereoselective inhibition of Neurotoxicologically significant Esterases and to assess the potential of these compounds to cause organophosphorus (OP) compound-induced delayed Neurotoxicity (OPIDN). The order of potencies against hen brain AChE was (1R, 3R) > (1R, 3S) > (1RS, 3RS) > (1S, 3R) > (1S, 3S), with a 15-fold difference between the strongest (ki = 388 mM-1 min-1; 20 min I50 = 89.3 nM) and weakest (ki = 25.6 mM-1 min-1; 20 min I50 = 1354 nM) inhibitors. Both asymmetric centers contributed substantially and interdependently to inhibitory potency, but the effect of changing the configuration at phosphorus alone was greater than changing the configuration at carbon alone. None of the isomalathions was an effective inhibitor of hen brain NTE (extrapolated 20 min I50 values were 1.2 to 29 mM), yielding NTE/ AChE I50 ratios (neuropathy target ratios, NTRs) of 1.5 x 10(3) to 1.5 x 10(5). NTRs of this magnitude indicate that none of the isomalathions should initiate OPIDN, even after doses greatly exceeding the LD50. Therefore, reports of OPIDN or other neuropathic sequelae associated with malathion exposures in humans cannot be explained on the basis of NTE inhibition by contaminating isomalathions.
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Chlorpyrifos: Assessment of Potential for Delayed Neurotoxicity by Repeated Dosing in Adult Hens with Monitoring of Brain AcetylcholinEsterase, Brain and Lymphocyte Neurotoxic Esterase, and Plasma ButyrylcholinEsterase Activities
Fundamental and Applied Toxicology, 1993Co-Authors: Rudy J. Richardson, Thomas B. Moore, Usamah S. Kayyali, Joseph C. RandallAbstract:Chlorpyrifos: Assessment of Potential for Delayed Neurotoxicity by Repeated Dosing in Adult Hens with Monitoring of Brain AcetylcholinEsterase, Brain and Lymphocyte Neurotoxic Esterase, and Plasma ButyrylcholinEsterase Activities. Richardson, R. J., Moore, T. B., Kayyali, U. S., and Randall, J. C. (1993). Fundam. Appl. Toxicol. 21, 89-96. Previous work has shown that acute exposures to chlorpyrifos (CPS; diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate) cannot produce >70% inhibition of brain Neurotoxic Esterase (NTE) and cause organophosphorus compound-induced delayed Neurotoxicity (OPIDN) unless the dose is well in excess of the LD50, necessitating aggressive therapy for cholinergic toxicity. The present study was carried out to determine if repeated doses of CPS at the maximum tolerated daily dose without prophylaxis against cholinergic toxicity could cause cumulative inhibition of NTE and OPIDN. Adult hens were dosed daily for 20 days with CPS (10 mg/kg/day po in 2 ml/kg corn oil) or corn oil (vehicle control) (2 ml/kg/day po) and observed for an additional 4 weeks. Brain acetylcholinEsterase (AChE), brain and lymphocyte NTE, and plasma butyrylcholinEsterase (BuChE) activities were assayed on Days 0 (control only), 4, 10, 15, 20, and 48. During Days 4-20, brain AChE and plasma BuChE activities from CPS-treated hens were inhibited 58-70% and 49-80% of contemporaneous controls, respectively. At 4 weeks after the end of dosing, brain AChE activity in treated birds had recovered to 86% of control and plasma BuChE activity was 134% of control. Brain and lymphocyte NTE activities of treated animals throughout the study were 82-99% and 85-128% of control, respectively. Neither brain nor lymphocyte NTE activities in treated hens exhibited cumulative inhibition. The 18% inhibition of brain NTE seen on days 10 and 20 was significantly, but substantially below the putative threshold for OPIDN. Body weight of treated hens decreased 10-25% during Days 4-20 and recovered to 87% of control by the end of the study. Some treated hens developed a slight staggering gait during the first week of dosing, which disappeared by the second week. Throughout the 4-week observation period, all hens appeared normal and were able to perch on a horizontal rod. The results indicate that daily dosing with CPS at a level sufficient to cause significant loss of body weight as well as marked inhibition of brain AChE and plasma BuChE resulted in no significant change in lymphocyte NTE activity, a maximum inhibition of brain NTE of 18%, no cumulative inhibition of lymphocyte or brain NTE, and no clinical signs of OPIDN.
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Inhibition of Hen Brain AcetylcholinEsterase and Neurotoxic Esterase by Chlorpyrifos in Vivo and Kinetics of Inhibition by Chlorpyrifos Oxon in Vitro: Application to Assessment of Neuropathic Risk
Fundamental and Applied Toxicology, 1993Co-Authors: Rudy J. Richardson, Thomas B. Moore, Usamah S. Kayyali, Jay H. Fowke, Joseph C. RandallAbstract:Chlorpyrifos (CPS; O,O-diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate; Dursban) is a widely used broad-spectrum organophosphorus (OP) insecticide. Because some OP compounds can cause a sensory-motor distal axonopathy called OP compound-induced delayed Neurotoxicity (OPIDN), CPS has been evaluated for this paralytic effect. Early studies of the Neurotoxicity of CPS in young and adult hens reported reversible leg weakness but failed to detect OPIDN. More recently, a human case of mild OPIDN was reported to result from ingestion of a massive dose (about 300 mg/kg) in a suicide attempt. Subsequent experiments in adult hens (the currently accepted animal model of choice for studies of OPIDN) showed that doses of CPS in excess of the LD50 in atropine-treated animals inhibited brain Neurotoxic Esterase (NTE) and produced mild to moderate ataxia. Considering the extensive use of CPS and its demonstrated potential for causing OPIDN at supralethal doses, additional data are needed to enable quantitative estimates to be made of the neuropathic risk of this compound. Previous work has shown that the ability of OP insecticides to cause acute cholinergic toxicity versus OPIDN can be predicted from their relative tendency to inhibit the intended target, acetylcholinEsterase (AChE), versus the putative neuropathic target, NTE, in brain tissue. The present study was designed to clarify the magnitude of neuropathic risk associated with CPS exposures by measuring hen brain AChE and NTE inhibition following dosing in vivo and determining the bimolecular rate constant of inhibition (ki) for each enzyme by the active metabolite, CPS oxon (CPO), in vitro. CPS administered to atropine-treated adult hens at 0, 75, 150, and 300 mg/kg po in corn oil produced mean values for brain AChE inhibition 4 days after dosing of 0, 58, 75, and 86%, respectively, and mean values for brain NTE inhibition of 0, 21, 40, and 77%, respectively. Only the high dose (six times the unprotected LD50 in hens) produced NTE inhibition above the presumed threshold of 70%, and these animals were in extremis from cholinergic toxicity at the time of euthanization despite continual treatment with atropine. When 150 mg/kg CPS po in corn oil was given to atropine-treated hens on Day 0, inhibition on Days 1, 2, 4, 8, and 16 for brain AChE was 86, 82, 72, 44, and 29%, respectively, and for brain NTE was 30, 28, 38, 29, and 6%, respectively. No signs of OPIDN were observed in any of the animals during the 16-day study period. Kinetic studies of the inhibition of hen brain AChE and NTE by CPO in vitro demonstrated that CPO exhibits high potency and extraordinary selectivity for its intended target, AChE. The ki values were 15.5 μ m −1 min−1 for AChE and 0.145 μ m −1 min−1 for NTE. The calculated fixed-time (20-min) I50 values were 2.24 n m for AChE and 239 n m for NTE, yielding an I50 ratio for NTE/AChE of 107. These results may be compared with data compiled for other OP compounds with respect to NTE/AChE I50 ratios and the corresponding doses required to produce OPIDN relative to the LD50. In general, NTE/AChE I50 ratios greater than 1 indicate that the dose required to produce OPIDN is greater than the LD50. Taken together, the results of this study indicate that acute exposures to CPS would not be expected to cause OPIDN except under extreme conditions such as attempted suicides involving medically assisted survival of doses considerably in excess of the LD50.
Frederick W. Oehme - One of the best experts on this subject based on the ideXlab platform.
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the effect of a single oral dose of tri o cresyl phosphate on Neurotoxic Esterase and acetylcholinEsterase activities in the central nervous system erythrocytes and plasma
Veterinary and Human Toxicology, 1994Co-Authors: D S Barrett, Frederick W. OehmeAbstract:This study reports the activity of Neurotoxic Esterase (NTE) and acetylcholinEsterase (AChE) in the blood and central nervous system (CNS) of swine 6, 12, 24 and 48 h after a single oral dose of 800 mg tri-o-cresyl phosphate (TOCP)/kg. At all evaluated intervals, inhibition of NTE activity in leukocytes and the CNS was 88% or higher, with only slight differences in NTE inhibition apparent among the various tissues examined. This extreme inhibition of NTE activity precluded correlation between inhibition of NTE in peripheral leukocytes and the CNS. However, the similarity in NTE response in leukocytes and the CNS following TOCP administration indicates the potential for leukocyte NTE as a biochemical marker for organophosphorus ester-induced delayed Neurotoxicity (OPIDN) development. As the distribution pattern of NTE in the CNS of swine closely parallels that of man, these results further suggest that swine may prove a useful animal model for the study of OPIDN. The activity of AChE was highly variable based on time of assay and tissue examined. In general, plasma AChE activity was more severely depressed in all animals and responded more rapidly to TOCP administration. However, erythrocyte AChE more accurately reflected the enzyme's activity in the CNS and the clinical response to TOCP. Based on the data provided by this study, a threshold inhibition of erythrocyte AChE between 59 and 74% is required for production of acute cholinergic signs.
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Clinical manifestations and leukocyte Neurotoxic Esterase and red blood cell and plasma acetylcholinEsterase activities in swine following a single oral dose of tri-o-cresyl phosphate
Veterinary and human toxicology, 1994Co-Authors: Frederick W. Oehme, S.m. Kruckenberg, J.e. SmithAbstract:We report the clinical signs and the effects on leukocyte Neurotoxic Esterase and red blood cell and plasma acetylcholinEsterase (AChE) activities in swine orally administered a single dose of tri-o-cresyl phosphate (TOCP) at 400, 800 or 1000 mg/kg. Swine in all dosage groups exhibited signs consistent with inhibition of nervous tissue cholinEsterase 3-48 h after TOCP administration. Onset was dose-related, and 2/3 1000 mg/kg dosed swine died 3 or 35 h postdosing. In surviving swine, significant depressions in plasma AChE activity were apparent at 6 h postdosing, ranging from 16-23% of predosing levels. Similar depressions of red blood cell AChE were not observed until 24 h postdosing. Plasma AChE activities appeared to more accurately reflect the development of acute cholinergic signs observed in the 1000 mg/kg dosed swine at 3 h postdosing while red blood cell AChE activities were more consistent with the delayed cholinergic signs exhibited by the 400 and 800 mg/kg dosed swine at 24 h postdosing. All survivors developed signs of delayed Neurotoxicity 10-12 d after TOCP administration, and 70% or greater inhibition of Neurotoxic Esterase activity in leukocytes was apparent during the first 48 h postdosing.
Joseph C. Randall - One of the best experts on this subject based on the ideXlab platform.
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Inhibition of Neurotoxic Esterase in Vitro by Novel Carbamates
Toxicology and Applied Pharmacology, 1997Co-Authors: Joseph C. Randall, Jeffrey L. Ambroso, William C. Groutas, Michael J. Brubaker, Rudy J. RichardsonAbstract:Carbamyl sulfonate (CS) compounds are a novel class of carbamates derived from amino acid methyl esters. They have the general structure RCH(COOCH3)NH(CO)SO-3K+, where R is the sidechain of the parent amino acid. These compounds were developed as active site-directed inhibitors of human leukocyte elastase (HLE). The purpose of this study was to characterize the inhibition of hen brain Neurotoxic Esterase (neuropathy target Esterase, NTE), horse serum butyrylcholinEsterase (BuChE), and bovine erythrocyte acetylcholinEsterase (AChE) by CS analogs derived from the methyl esters of L-ala, D-norval, L-norval, L-phe, L-val, L-norleu, D-met, and L-met. Bimolecular rate constants of inhibition (ki) for NTE ranged from 0.571 for L-ala-CS to 17.7 mM-1 min-1 for L-norleu-CS (10-min I50 values of 123 and 3.92 microM, respectively). Potency against NTE increased with chain length for straight-chain R-groups of L-CS compounds. Unlike HLE, NTE was only weakly stereoselective for CS compound enantiomers. The L-isomers were weaker inhibitors of BuChE than NTE (10-min I50 range of 742 to 35.6 microM). In contrast to the L-enantiomers, the I50 plots of D-met-CS and D-norval-CS were not linear for BuChE, suggesting a possible stereospecific mechanistic shift for inhibition of this enzyme, AChE was not effectively inhibited by any of the CS compounds (I50 values > 750 microM). The specificity and charged nature of CS compounds give these unusual NTE inhibitors potential advantages for mechanistic studies of organophosphorus compound-induced delayed Neurotoxicity (OPIDN) and its protection or potentiation.
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Chlorpyrifos: Assessment of Potential for Delayed Neurotoxicity by Repeated Dosing in Adult Hens with Monitoring of Brain AcetylcholinEsterase, Brain and Lymphocyte Neurotoxic Esterase, and Plasma ButyrylcholinEsterase Activities
Fundamental and Applied Toxicology, 1993Co-Authors: Rudy J. Richardson, Thomas B. Moore, Usamah S. Kayyali, Joseph C. RandallAbstract:Chlorpyrifos: Assessment of Potential for Delayed Neurotoxicity by Repeated Dosing in Adult Hens with Monitoring of Brain AcetylcholinEsterase, Brain and Lymphocyte Neurotoxic Esterase, and Plasma ButyrylcholinEsterase Activities. Richardson, R. J., Moore, T. B., Kayyali, U. S., and Randall, J. C. (1993). Fundam. Appl. Toxicol. 21, 89-96. Previous work has shown that acute exposures to chlorpyrifos (CPS; diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate) cannot produce >70% inhibition of brain Neurotoxic Esterase (NTE) and cause organophosphorus compound-induced delayed Neurotoxicity (OPIDN) unless the dose is well in excess of the LD50, necessitating aggressive therapy for cholinergic toxicity. The present study was carried out to determine if repeated doses of CPS at the maximum tolerated daily dose without prophylaxis against cholinergic toxicity could cause cumulative inhibition of NTE and OPIDN. Adult hens were dosed daily for 20 days with CPS (10 mg/kg/day po in 2 ml/kg corn oil) or corn oil (vehicle control) (2 ml/kg/day po) and observed for an additional 4 weeks. Brain acetylcholinEsterase (AChE), brain and lymphocyte NTE, and plasma butyrylcholinEsterase (BuChE) activities were assayed on Days 0 (control only), 4, 10, 15, 20, and 48. During Days 4-20, brain AChE and plasma BuChE activities from CPS-treated hens were inhibited 58-70% and 49-80% of contemporaneous controls, respectively. At 4 weeks after the end of dosing, brain AChE activity in treated birds had recovered to 86% of control and plasma BuChE activity was 134% of control. Brain and lymphocyte NTE activities of treated animals throughout the study were 82-99% and 85-128% of control, respectively. Neither brain nor lymphocyte NTE activities in treated hens exhibited cumulative inhibition. The 18% inhibition of brain NTE seen on days 10 and 20 was significantly, but substantially below the putative threshold for OPIDN. Body weight of treated hens decreased 10-25% during Days 4-20 and recovered to 87% of control by the end of the study. Some treated hens developed a slight staggering gait during the first week of dosing, which disappeared by the second week. Throughout the 4-week observation period, all hens appeared normal and were able to perch on a horizontal rod. The results indicate that daily dosing with CPS at a level sufficient to cause significant loss of body weight as well as marked inhibition of brain AChE and plasma BuChE resulted in no significant change in lymphocyte NTE activity, a maximum inhibition of brain NTE of 18%, no cumulative inhibition of lymphocyte or brain NTE, and no clinical signs of OPIDN.
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Inhibition of Hen Brain AcetylcholinEsterase and Neurotoxic Esterase by Chlorpyrifos in Vivo and Kinetics of Inhibition by Chlorpyrifos Oxon in Vitro: Application to Assessment of Neuropathic Risk
Fundamental and Applied Toxicology, 1993Co-Authors: Rudy J. Richardson, Thomas B. Moore, Usamah S. Kayyali, Jay H. Fowke, Joseph C. RandallAbstract:Chlorpyrifos (CPS; O,O-diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate; Dursban) is a widely used broad-spectrum organophosphorus (OP) insecticide. Because some OP compounds can cause a sensory-motor distal axonopathy called OP compound-induced delayed Neurotoxicity (OPIDN), CPS has been evaluated for this paralytic effect. Early studies of the Neurotoxicity of CPS in young and adult hens reported reversible leg weakness but failed to detect OPIDN. More recently, a human case of mild OPIDN was reported to result from ingestion of a massive dose (about 300 mg/kg) in a suicide attempt. Subsequent experiments in adult hens (the currently accepted animal model of choice for studies of OPIDN) showed that doses of CPS in excess of the LD50 in atropine-treated animals inhibited brain Neurotoxic Esterase (NTE) and produced mild to moderate ataxia. Considering the extensive use of CPS and its demonstrated potential for causing OPIDN at supralethal doses, additional data are needed to enable quantitative estimates to be made of the neuropathic risk of this compound. Previous work has shown that the ability of OP insecticides to cause acute cholinergic toxicity versus OPIDN can be predicted from their relative tendency to inhibit the intended target, acetylcholinEsterase (AChE), versus the putative neuropathic target, NTE, in brain tissue. The present study was designed to clarify the magnitude of neuropathic risk associated with CPS exposures by measuring hen brain AChE and NTE inhibition following dosing in vivo and determining the bimolecular rate constant of inhibition (ki) for each enzyme by the active metabolite, CPS oxon (CPO), in vitro. CPS administered to atropine-treated adult hens at 0, 75, 150, and 300 mg/kg po in corn oil produced mean values for brain AChE inhibition 4 days after dosing of 0, 58, 75, and 86%, respectively, and mean values for brain NTE inhibition of 0, 21, 40, and 77%, respectively. Only the high dose (six times the unprotected LD50 in hens) produced NTE inhibition above the presumed threshold of 70%, and these animals were in extremis from cholinergic toxicity at the time of euthanization despite continual treatment with atropine. When 150 mg/kg CPS po in corn oil was given to atropine-treated hens on Day 0, inhibition on Days 1, 2, 4, 8, and 16 for brain AChE was 86, 82, 72, 44, and 29%, respectively, and for brain NTE was 30, 28, 38, 29, and 6%, respectively. No signs of OPIDN were observed in any of the animals during the 16-day study period. Kinetic studies of the inhibition of hen brain AChE and NTE by CPO in vitro demonstrated that CPO exhibits high potency and extraordinary selectivity for its intended target, AChE. The ki values were 15.5 μ m −1 min−1 for AChE and 0.145 μ m −1 min−1 for NTE. The calculated fixed-time (20-min) I50 values were 2.24 n m for AChE and 239 n m for NTE, yielding an I50 ratio for NTE/AChE of 107. These results may be compared with data compiled for other OP compounds with respect to NTE/AChE I50 ratios and the corresponding doses required to produce OPIDN relative to the LD50. In general, NTE/AChE I50 ratios greater than 1 indicate that the dose required to produce OPIDN is greater than the LD50. Taken together, the results of this study indicate that acute exposures to CPS would not be expected to cause OPIDN except under extreme conditions such as attempted suicides involving medically assisted survival of doses considerably in excess of the LD50.
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Neurotoxic Esterase (NTE) Assay: Optimized Conditions Based on Detergent-Induced Shifts in the Phenol/ 4-Aminoantipyrine Chromophore Spectrum*
Journal of Analytical Toxicology, 1991Co-Authors: Usamah S. Kayyali, Thomas B. Moore, Joseph C. Randall, Rudy J. RichardsonAbstract:An assay for Neurotoxic Esterase (neuropathy target asterase, NTE) was developed by Johnson (1,2) to assess the delayed Neurotoxic potential of organophosphorus compounds. NTE activity is calculated from the rate of phenyl valerate hydrolysis resistant to paraoxon and sensitive to mipafox inhibition under specified conditions of inhibitor concentrations, pH, temperature, and incubation times with inhibitors and substrate. The amount of phenol produced is measured colorimetrically after its oxidative coupling with 4aminoantipyrine to yield 4-N-(1,4-benzoquinoneimine)antipyrine, a chromophore with a wavelength of maximum absorbance (Lm)510 nm and corresponding molar absorptivity (molar extinction coefficient, ~) equal to 13,900 M-lcm-L The assay was improved and simplified later by Johnson (3) without any change in the ~-m or ~, even though the chromophore solvent was altered by adding the detergent, sodium dodecyl sulfate (SDS). The present work demonstrates that when the NTE assay is performed according to the improved procedure, with a final [SDS] of 3.0 mg/mL, the ~.rn of the chromophore in the assay mixture is shifted from 510 to 490 nm. The same shift in the chromophore ~rn is observed when phenol standards are coupled with 4-aminoantipyrine in solutions containing 3.0 mg/mL SDS. A systematic investigation of the dependence of the ~-m of the chromophore on [SDS] in the assay mixture revealed that the spectral shift increases rapidly at an [SDS] greater than the apparent critical micelle concentration (CMC; estimated to be 0.53 mg/mL under these conditions) and begins to plateau at [SDS] greater than 10 mg/mL. Furthermore, the sensitivity of the assay was shown to be dependent upon [SDS], reaching a peak ~- value of 16,470 M-~cm -~ at a Lm of 486 nm when the final [SDS] was 9.5 mg/mL; it is therefore recommended that these optimized values of [SDS], Lm, and ~" be adopted in the NTE assay. Finally, because there are versions of assays for other enzymes or metabolites (e.g., acetylcholinEsterase, butyrylcholinEsterase, glucose, triglycerides, and uric acid) that rely on the same or a related chromophore as used in the NTE assay (4-8), the potential for detergent-induced shifts in the chromophore spectrum should be taken into account when optimizing these assays in the presence of detergents.
Marion Ehrich - One of the best experts on this subject based on the ideXlab platform.
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Organophosphorus-Induced Delayed Neuropathy
Hayes' Handbook of Pesticide Toxicology, 2010Co-Authors: Marion Ehrich, Bernard S. JortnerAbstract:Publisher Summary OPIDN is a generally progressive, irreversible disorder that causes clinical manifestations appearing days to weeks after humans and certain species of animals are exposed to OP compounds that can essentially irreversibly inhibit most of the available NTE (Neurotoxic Esterase). The severity of OPIDN, as indicated by clinical and pathological manifestations, depends on the species and age of test animals and the extent of NTE inhibition. Most of the victims of OPIDN have been people and animals exposed to OP agents that are used as lubricants and plasticizers rather than insecticides. OPIDN has been suggested to be involved in other disorders, such as that seen in veterans returning from the 1991 Gulf War. The neuropathy can be prevented by pretreatment with NTE inhibitors; however, these same compounds promote OPIDN when given after a neuropathy-inducing OP compound. A reliable experimental model of OPIDN can be obtained by single or multiple dosing in the domestic hen and the spectrum of nervous system alterations in that species has been documented previously in some detail. One factor known to be important in the initiation of OPIDN is inhibition of NTE (also known as Neurotoxic Esterase). This enzyme is a molecular target of neuropathy-inducing OP compounds with a pentavalent phosphorus atom, but NTE may be more of a biomarker rather than the single, specific target that initiates OPIDN.
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Development of a model cell culture system in which to study early effects of neuropathy-inducing organophosphorus esters
Toxicology Letters, 1992Co-Authors: A.c. Nostrandt, Marion EhrichAbstract:Certain organophosphorus (OP) compounds produce a delayed neuropathy in man and susceptible animal species after early inhibition and aging of the enzyme, Neurotoxic Esterase (NTE). In this study, the human neuroblastoma cell line, SY-5Y, was used to examine the time course of inhibition and aging of NTE after toxicant treatment. The time course and extent of detrimental effects on this enzyme were similar in the SY-5Y cells to those observed in homogenized chicken brain tissue after the same treatments. The results indicate that the SY-5Y model system shows promise for use in the determination of initial mechanisms contributing to the development of organophosphorus-induced delayed neuropathy.
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Comparative dose-response studies of organophosphorus ester-induced delayed neuropathy in rats and hens administered mipafox.
Neurotoxicology, 1992Co-Authors: K. R. Dyer, Bernard S. Jortner, L. G. Shell, Marion EhrichAbstract:A single injection of mipafox was administered to both long-Evans hooded rats and White leghorn hens in dosages which inhibited the activity of brain Neurotoxic Esterase 30-50%, 60-80%, or greater than 80% four hr after intoxication. All animals were monitored for clinical evidence of organophosphorus induced delayed neuropathy for 27 days, euthanatized, and regions of the nervous system were histologically evaluated. Only hens manifested clinical signs of neuropathy; however, light and electron microscopic lesions were present in the nervous systems of both species. In rats, these lesions were well developed in only the highest dosage group and confined to the rostral level of the fasciculus gracilis in the medulla oblongata
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A microassay method for Neurotoxic Esterase determinations.
Fundamental and Applied Toxicology, 1991Co-Authors: Linda Correll, Marion EhrichAbstract:A microtiter plate reader with an associated computer to average triplicate samples and subtract blanks was used for reading and calculating Neurotoxic Esterase (NTE, also known as neuropathy target Esterase) activities in spinal cord regions of hens 4 hr after administration of diisopropylphosphorofluoridate (DFP, 0.5 mg/kg sc). Although NTE inhibition is an early indicator of organophosphorus ester-induced delayed neuropathy, DFP-induced inhibition was not greater in regions of the spinal cord where pathological changes are most notable. AcetylcholinEsterase (AChE) activities and protein determinations were also done on these tissues using microassay methods. DFP-induced AChE inhibition was similar to NTE inhibition. In addition to the capability to be used for small regional Esterase activity measurements, the microassay was advantageous because the number of samples incorporated into a single assay was increased and the time needed for the NTE assay was reduced by 50%. Total volume of incubate in each well was 0.3 ml; the incubate contained 120 quantities of sample and reagents necessary in more conventional assays. Validation of the microassay was performed by comparison with more conventional assays when measuring inhibition of NTE and AChE in brains of control and experimental hens of two different genetic strains (B13B13 and B21B21 white leghorns). Experimental birds were given DFP, 0.5 mg/kg sc, 24 hr before samples were collected. NTE activities in brains of control hens were similar using both types of NTE analytical procedures. Percentage inhibition of NTE caused by DFP was within 4% using both assay procedures in both strains of hens. The microassay was sensitive enough to detect NTE activity in 42 μg of hen brain after 15 min of incubation. Hen lymphocytes could also be examined for effects of organophosphorus esters on NTE activity, with 14.1 ± 2.2 and 8.3 ± 2.2 μmol/15 min/mg protein in 1 × 106 cells measured in samples taken before and 4 hr after administration of 0.5 mg/kg sc DFP.