Biosensor Detection of Neuropathy Target Esterase in Whole Blood as a Biomarker of Exposure to Neuropathic Organophosphorus Compounds (original) (raw)
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Human & …, 2007
Organophosphates (OPs) that inhibit neuropathy target esterase (NTE) with subsequent ageing can produce OPinduced delayed neuropathy (OPIDN). NTE inhibition in lymphocytes can be used as a biomarker of exposure to neuropathic OPs. An electrochemical method was developed to assay NTE in whole blood. The high sensitivity of the tyrosinase carbon-paste biosensors for the phenol produced by hydrolysis of the substrate, phenyl valerate, allowed NTE activity to be measured in diluted samples of whole blood, which cannot be done using the standard colorimetric assay. The biosensor was used to establish correlations of NTE inhibitions in blood with that in lymphocytes and brain after dosing hens with a neuropathic OP. The results of further studies demonstrated that whole blood NTE is a reliable biomarker of neuro-pathic OPs for up to 96 hours after exposure. These validation results suggest that the biosensor NTE assay for whole blood could be developed to measure human exposure to neuropathic OPs as a predictor of OPIDN. The small blood volume required (100 mL), simplicity of sample preparation and rapid analysis times indicate that the biosensor should be useful in biomonitoring and epidemiological studies. The present paper is an overview of our previous and ongoing work in this area. Human & Experimental Toxicology (2007) 26, 273 Á 282
Journal of Applied Toxicology, 2016
The adult hen is the standard animal model for testing organophosphorus (OP) compounds for organophosphorus compound-induced delayed neurotoxicity (OPIDN). Recently, we developed a mouse model for biochemical assessment of the neuropathic potential of OP compounds based on brain neuropathy target esterase (NTE) and acetylcholinesterase (AChE) inhibition. We carried out the present work to further develop the mouse model by testing the hypothesis that whole blood NTE inhibition could be used as a biochemical marker for exposure to neuropathic OP compounds. Because brain NTE and AChE inhibition are biomarkers of OPIDN and acute cholinergic toxicity, respectively, we compared NTE and AChE 20-min IC 50 values as well as ED 50 values 1 h after single intraperitoneal (i.p.) injections of increasing doses of two neuropathic OP compounds that differed in acute toxicity potency. We found good agreement between the brain and blood for in vitro sensitivity of each enzyme as well for the ratios IC 50 (AChE)/IC 50 (NTE). Both OP compounds inhibited AChE and NTE in the mouse brain and blood dosedependently, and brain and blood inhibitions in vivo were well correlated for each enzyme. For both OP compounds, the ratio ED 50 (AChE)/ED 50 (NTE) in blood corresponded to that in the brain despite the somewhat higher sensitivity of blood enzymes. Thus, our results indicate that mouse blood NTE could serve as a biomarker of exposure to neuropathic OP compounds. Moreover, the data suggest that relative inhibition of blood NTE and AChE provide a way to assess the likelihood that OP compound exposure in a susceptible species would produce cholinergic and/or delayed neuropathic effects.
Blood esterases as a complex biomarker for exposure to organophosphorus compounds
2009
The growing threat of international terrorism brings with it new scenarios for disaster. For example, in the case of toxic organophosphorus compounds (OPs), it possible for terrorists to use known agents or inadvertently to produce highly toxic OPs of unknown structure as the result of attacks on chemical plants or stockpiles of pesticides and other chemicals. Defending against such agents requires rapid, sensitive, and specific detection of them and their biological effects. Thus, the development of biomarkers of human exposures to OPs is a vital component of the system of prediction and early diagnosis of induced diseases. The phosphylating properties of OPs lead to their differential interactions with various serine esterases. These enzymes include primary targets, e.g., acetylcholinesterase (AChE, acute toxicity) and neuropathy target esterase (NTE, delayed neuropathy, OPIDN); as well as secondary targets, e.g., butyrylcholinesterase (BChE) and carboxylesterase (CaE), which act as scavengers of OPs. The set of activities of these esterases as well as that of paraoxonase (PON1), which can hydrolyze and detoxify OPs, constitutes the "esterase status" of an organism that largely determines indi-vidual sensitivity to OPs and that may be used as a complex biomarker of exposure. This complex biomarker is more effective and informative than the standard determination of erythrocyte AChE and total blood cholinesterases. In particular, it assists with distinguishing between acute and delayed neurotoxicity induced by OPs, as we showed in experiments on acute exposure of hens to a neuropathic compound, O,O-dipropyl-O-dichlorovinyl phosphate. In addition, measuring decreased activities of BChE and CaE, which are often more sensitive biomarkers of OP exposure, allows us to reveal exposure to low doses, as demonstrated by treating mice with low doses of phosphorylated oximes. The aim of the ISTC Project summarized here is to develop a smart biosensor system for simultaneous analysis of a set of blood esterases including AChE, BChE, NTE, CaE, and PON1. The speed, sensitivity, and integrated approach of the method will allow hazards to be assessed and appropriate interventions to be recommended before overt toxic damage has occurred.
Neuropathy Target Esterase in Human Lymphocytes
Archives of Environmental Health: An International Journal, 1985
Measurement of neuropathy target esterase activity (NTE) in blood lymphocytes has been suggested as a possible biomonitor for organophosphate-induced delayed polyneuropathy. Human lymphocyte NTE was characterized in vitro according to the sensitivity to several organophosphate inhibitors, which was found similar to that of the nervous system enzyme. Methods for collection, storage, and processing of blood and the NTE assay are described (averaged coefficient of variation of the method is 8%). The mean (± SO) value of lymphocyte NTE activity in a caucasian population (108 healthy subjects) was 11.5 ± 2.5 nMoles/min • mg of protein. No sex or age differences were detected. The averaged intraindividual coefficient of variation was 1().1%. These results suggest the feasibility of the test in clinical conditions, a sufficient reproducibility of the test, and a large interindividual variation. Appropriate baseline values are advisable when using the test to evaluate the effects of an occupational exposure to organophosphorus esters which may cause delayed polyneuropathy.
A new approach for determination of neuropathy target esterase activity
Chemico-Biological Interactions, 1999
Neuropathy target esterase (NTE) was shown to be an excellent biochemical marker for screening of organophosphates (OPs) with respect to their ability to result in organophosphate induced delayed neurotoxicity (OPIDN). This paper describes a new biosensor approach to the analysis of NTE and its inhibitors. The method is based on the combination of NTE enzymatic hydrolysis of phenyl valerate (PV) with phenol detection by the Clarktype oxygen electrode modified by immobilized tyrosinase. The validity of this biosensor method is confirmed by the facts that the calibration curves for NTE obtained by colorimetric and flow-through electrochemical methods were nearly identical and the titration of NTE by test inhibitor mipafox was shown to yield the same pI 50 values. The developed electrochemical methods can be considered as a promising approach both for serial express NTE analysis and for kinetic characteristics of NTE.
Chemico-Biological Interactions, 2010
This paper reviews our previously published data and presents new results on biosensor assay of blood esterases. Tyrosinase and choline oxidase biosensors based on nanostructured polyelectrolyte films were developed for these purposes. Experiments were performed on the quantitative determination of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), and neuropathy target esterase (NTE) in samples of whole blood of rats, mice, and humans. Good agreement was found between biosensor and spectrophotometric assays for AChE, BChE, and CaE. No direct comparison could be made for NTE because its activity cannot be measured spectrophotometrically in whole blood. A new method of simultaneous quantitative determination of AChE and BChE in test mixtures is also described. This method represents a bifunctional biosensor for the simultaneous analysis of choline and phenol based on integration of individual sensors. Algorithms for calculation of separate concentrations of AChE and BChE in the mixture were developed. The mean error of calculated component concentrations was ∼6% for binary test mixtures. The present work provides a foundation for building multiplexed systems for the simultaneous determination of multiple esterases with applications to biomonitoring for exposures to organophosphorus compounds.
Bioelectrochemical Analysis of Neuropathy Target Esterase Activity in Blood
Analytical …, 2001
Bioelectrochemical analysis of neuropathy target esterase (NTE) and its inhibitors is based on the combination of the NTE-catalyzed hydrolysis of phenyl valerate and phenol detection by a tyrosinase carbon-paste electrode. The use of the tyrosinase electrode improves 10-fold the sensitivity of NTE detection in comparison with a spectrophotometric method. The tyrosinase electrode was found to be suitable for measurements in whole human blood where spectrophotometric detection is considerably restricted. The specificity of NTE in blood for mipafox and di-2-propyl phosphorofluoridate was close to that for neuronal NTE. The NTE-like activity in blood was determined to be 0.19 ± 0.02 nmol/min/mg of protein.