Neuropathy target esterase (NTE) and organophosphorus-induced delayed polyneuropathy (OPIDP): recent advances

Prediction of dose-dependent in vivo acetylcholinesterase inhibition by profenofos in rats and humans using physiologically based kinetic (PBK) modeling-facilitated reverse dosimetry

Organophosphate pesticides (OPs) are known to inhibit acetylcholine esterase (AChE), a critical effect used to establish health-based guidance values. This study developed a combined in vitro–in silico approach to predict AChE inhibition by the OP profenofos in rats and humans. A physiologically based kinetic (PBK) model was developed for both species. Parameter values for profenofos conversion to 4-bromo-2-chlorophenol (BCP) were derived from in vitro incubations with liver microsomes, liver cytosol, and plasma from rats (catalytic efficiencies of 1.1, 2.8, and 0.19 ml/min/mg protein, respectively) and humans (catalytic efficiencies of 0.17, 0.79, and 0.063 ml/min/mg protein, respectively), whereas other chemical-related parameter values were derived using in silico calculations. The rat PBK model was evaluated against literature data on urinary excretion of conjugated BCP. Concentration-dependent inhibition of rat and human AChE was determined in vitro and these data were translated with the PBK models to predicted dose-dependent AChE inhibition in rats and humans in vivo. Comparing predicted dose-dependent AChE inhibition in rats to literature data on profenofos-induced AChE inhibition revealed an accurate prediction of in vivo effect levels. Comparison of rat predictions (BMDL10 of predicted dose–response data of 0.45 mg/kg bw) and human predictions (BMDL10 of predicted dose–response data of 0.01 mg/kg bw) suggests that humans are more sensitive than rats, being mainly due to differences in kinetics. Altogether, the results demonstrate that in vivo AChE inhibition upon acute exposure to profenofos was closely predicted in rats, indicating the potential of this novel approach method in chemical hazard assessment.

Current approaches to enhancing oxime reactivator delivery into the brain

The misuse of organophosphate compounds still represents a current threat worldwide. Treatment of poisoning with organophosphates (OPs) remains unsatisfactorily resolved despite the extensive investment in research in academia. There are no universal, effective and centrally-active acetylcholinesterase (AChE) reactivators to countermeasure OP intoxication. One major obstacle is to overcome the blood-brain barrier (BBB). The central compartment is readily accessible by the OPs which are lipophilic bullets that can easily cross the BBB, whereas first-line therapeutics, namely oxime-based AChE reactivators and atropine, do not cross or do so rather slowly. The limitation of oxime-based AChE reactivators can be ascribed to their chemical nature, bearing a positive charge which is essential either for their AChE affinity or their reactivating potency. The aim of this article is to review the methods for targeting the brain by oxime reactivators that have been developed so far. Approaches using prodrugs, lipophilicity enhancement, or sugar-based oximes have been rather unsuccessful. However, other strategies have been more promising, such as the use of nanoparticles or co-administration of the reactivator with efflux transporter inhibitors. Encouraging results have also been associated with intranasal delivery, but research in this field is still at the beginning. Further research of auspicious approaches is inevitable.

Complex View on Poisoning with Nerve Agents and Organophosphates

OP/nerve agents are still considered as important chemicals acting on living organisms and widely used in human practice. Nerve agents are the most lethal chemical warfare agents. They are characterized according to their action as compounds influencing cholinergic nerve transmission via inhibition of AChE. The symptoms of intoxication comprise nicotinic, muscarinic and central symptoms, for some OP/nerve agents, a delayed neurotoxicity is observed. Cholinesterases (AChE and BuChE) are characterized as the main enzymes involved in the toxic effect of these compounds including their molecular forms. The activity of both enzymes (and molecular forms) is influenced by inhibitors and other factors such as pathological states. There are different methods for cholinesterase determination, however, the most frequent is the method based on the hydrolysis of thiocholine esters and following detection of free SH-group of the released thiocholine. The diagnosis of OP/nerve agents poisoning is based on anamnesis, the clinical status of the intoxicated organism and on cholinesterase determination in the blood. Some principles of prophylaxis against OP/nerve agents poisoning comprising the administration of reversible cholinesterase inhibitors such as pyridostigmine (alone or in combination with other drugs), scavengers such as preparations of cholinesterases, some therapeutic drugs and possible combinations are given. Basic principles of the treatment of nerve agents/OP poisoning are described. New drugs for the treatment are under experimental study based on new approaches to the mechanism of action.

Assessment of neurotoxic effects of tri-cresyl phosphates (TCPs) and cresyl saligenin phosphate (CBDP) using a combination of in vitro techniques

Environmental exposures to tri-cresyl phosphates (TCPs) and the possible formation of toxic metabolites (e.g. cresyl saligenin phosphate; CBDP) may cause a variety of neurotoxic effects in humans. As reported for other organophosphorus compounds (OPs), the inhibition of acetylcholine esterase (AChE) has also been proposed as the underlying mechanism for TCP neurotoxicity. The ortho-isomer, ToCP and its metabolite CBDP are also known to affect neuropathy target esterase (NTE) leading to organophosphate-induced delayed neuropathy (OPIDN). Recently, in vitro testing has led to the identification of other molecular targets and alternative mechanisms of ToCP toxicity. The metabolite CBDP and other isomers, as well as commercial mixtures have not been tested for such additional modes of actions. Accordingly, the present study investigates alterations of neurobiological correlates of central nervous processes using different in vitro techniques. The three symmetric TCP isomers - ToCP, TpCP, and TmCP - that contain a methyl group at the ortho-, para-, or meta-position of the aromatic ring system, respectively, together with a commercial TCP mixture, and CBDP were all tested using concentrations not exceeding their cytotoxic concentrations. Isolated cortical neurons were kept in culture for 6days followed by 24h incubation with different concentrations of the test compounds. Thus, all endpoints were assessed after 7days in vitro (DIV 7), at which time cell viability, neurite microstructure, and the function of glutamate receptors and voltage-gated calcium cannels (VGCC) were measured. While the cytotoxic potential of the TCP isomers and their mixture were comparable (IC₅₀≥80μM), CBDP was more cytotoxic (IC₅₀: 15μM) to primary cortical neurons. In contrast, CBDP (up to 10μM) did not compromise the microstructure of neurites. Ten μM of ToCP significantly reduced the size and complexity of neurite networks, but neither TmCP and TpCP nor the mixture affected this second endpoint of neurotoxicity assessment. TCPs and their mixture significantly reduced the Ca²⁺ influx in response to glutamate and KCl stimulation in concentrations of 10μM. Only ToCP showed a specific effect on glutamate receptors with 100nM reducing the evoked Ca²⁺ influx. The effects of CBDP on the provoked Ca²⁺ influx were much weaker than those observed for TCPs. These results confirmed that ToCP has a unique mode of action on glutamate receptors that are not observed with the metabolite CBDP and the other symmetric TCP isomers. In addition, the TmCP isomer seems to have the lowest potency with respect to inducing neurotoxic effects. CBDP did not affect the neurospecific endpoints investigated in this study. Therefore, the specific affinity of CBDP for NTE and the reported general cytotoxicity might be the most relevant modes of action of this toxic metabolite in the context of ToCP-induced neurotoxicity, including OPIDN.

In vitro study of the neuropathic potential of the organophosphorus compounds fenamiphos and profenofos: Comparison with mipafox and paraoxon

Organophosphorus-induced delayed neuropathy (OPIDN) is a central-peripheral distal axonopathy that develops 8-14 days after poisoning by a neuropathic organophosphorus compound (OP). Several OPs that caused OPIDN were withdrawn from the agricultural market due to induction of serious delayed effects. Therefore, the development of in vitro screenings able to differentiate neuropathic from non-neuropathic OPs is of crucial importance. Thus, the aim of this study was to evaluate the differences in the neurotoxic effects of mipafox (neuropathic OP) and paraoxon (non-neuropathic OP) in SH-SY5Y human neuroblastoma cells, using the inhibition and aging of neuropathy target esterase (NTE), inhibition of acetylcholinesterase (AChE), activation of calpain, neurite outgrowth, cytotoxicity and intracellular calcium as indicators. Additionally, the potential of fenamiphos and profenofos to cause acute and/or delayed effects was also evaluated. Mipafox had the lowest IC50 and induced the highest percentage of aging of NTE among the OPs evaluated. Only mipafox was able to cause calpain activation after 24 h of incubation. Concentrations of mipafox and fenamiphos which inhibited at least 70% of NTE were also able to reduce neurite outgrowth. Cytotoxicity was higher in non-neuropathic than in neuropathic OPs while the intracellular calcium levels were higher in neuropathic than in non-neuropathic OPs. In conclusion, the SH-SY5Y cellular model was selective to differentiate neuropathic from non-neuropathic OPs; fenamiphos, but not profenofos presented results compatible with the induction of OPIDN.

Loss-of-function mutations in PNPLA6 encoding neuropathy target esterase underlie pubertal failure and neurological deficits in Gordon Holmes syndrome

CONTEXT

Gordon Holmes syndrome (GHS) is characterized by cerebellar ataxia/atrophy and normosmic hypogonadotropic hypogonadism (nHH). The underlying pathophysiology of this combined neurodegeneration and nHH remains unknown.

OBJECTIVE

We aimed to provide insight into the disease mechanism in GHS.

METHODS

We studied a cohort of 6 multiplex families with GHS through autozygosity mapping and whole-exome sequencing.

RESULTS

We identified 6 patients from 3 independent families carrying loss-of-function mutations in PNPLA6, which encodes neuropathy target esterase (NTE), a lysophospholipase that maintains intracellular phospholipid homeostasis by converting lysophosphatidylcholine to glycerophosphocholine. Wild-type PNPLA6, but not PNPLA6 bearing these mutations, rescued a well-established Drosophila neurodegenerative phenotype caused by the absence of sws, the fly ortholog of mammalian PNPLA6. Inhibition of NTE activity in the LβT2 gonadotrope cell line diminished LH response to GnRH by reducing GnRH-stimulated LH exocytosis, without affecting GnRH receptor signaling or LHβ synthesis.

CONCLUSION

These results suggest that NTE-dependent alteration of phospholipid homeostasis in GHS causes both neurodegeneration and impaired LH release from pituitary gonadotropes, leading to nHH.

A phosphorylation-sensitive tyrosine-tailored magnetic particle for electrochemically probing free organophosphates in blood

Phosphorylation-sensitive tyrosine was coated onto Fe₃O₄ particles, resulting in a “lab-on-a-particle”-based electrochemical detection protocol for probing free organophosphates in blood.

Identification of differentially expressed proteins related to organophosphorus-induced delayed neuropathy in the brains of hens

Some organophosphorus compounds can cause organophosphate-induced delayed neuropathy (OPIDN). Incidents have been documented for decades, however, little is known about which proteins contribute to the initiation, progression and development of OPIDN. In this study, 51 hens were divided into three groups. The tri-ortho-cresyl-phosphate (TOCP) group was treated with 1000 mg kg(-1) TOCP whereas the control group was treated with an equivalent volume of vehicle. The PMSF + TOCP group was treated subcutaneously with 40 mg kg(-1) phenylmethylsulfonyl fluoride (PMSF), followed by 1000 mg kg(-1) TOCP 24 h later. Proteins in the brains of hens were separated by two-dimensional polyacrylamide gel electrophoresis on day 5 after TOCP administration. Mass spectrometry identified eight differentially expressed proteins. Among these proteins, downregulated expression of glutamine synthetase (GS) in the brains of hens after TOCP treatment was further confirmed by real time RT-PCR and ELISA. Moreover, the brains of hens exposed to TOCP exhibited increased levels of glutamate (Glu) and cytosolic calcium concentration ([Ca(2+)](i)), and a decreased level of glutamine (Gln). However, there were no significant differences in GS expression or levels of Glu, Gln, and [Ca(2+)](i) in the brains of hens among the groups on day 21 after TOCP administration. These results indicate that TOCP exposure downregulates GS expression in the brains of hens, and that downregulation of GS is accompanied by increased levels of Glu and [Ca(2+)](i) in the early stage after TOCP administration. It is also suggested that the downregulated expression of GS might be associated with OPIDN through the disruption of homeostasis of the Glu-Gln cycle and [Ca(2+) ](i).

Changes in beclin-1 and micro-calpain expression in tri-ortho-cresyl phosphate-induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP) can cause toxic neuropathy known as organophosphate-induced delayed neuropathy (OPIDN), which is pathologically characterized by the swollen axon containing aggregations of neurofilaments, microtubules, and multivesicular vesicles. Autophagy is a self-degradative process which plays a housekeeping role in removing misfolded proteins and damaged organelles. The current study was designed to investigate the possible roles of autophagy in the pathogenesis of OPIDN. Adult hens were treated with a dose of 750mg/kg TOCP by gavage, or injected subcutaneously with 60mg/kg phenylmethanesulfonyl fluoride (PMSF) dissolved in DMSO 24h earlier and subsequently treated with TOCP, then sacrificed on the time-points of 0, 1, 5, 10, and 21 days after dosing of TOCP respectively. The levels of beclin-1 and μ-calpain in tibial nerves and spinal cords were determined by immunoblotting. The results showed that in both tissues TOCP increased the expression of μ-calpain while decreased that of beclin-1. When given before TOCP administration, PMSF pretreatment could protect hens against the delayed neuropathy. In the meantime, pretreatment with PMSF reduced calpain expression below basal and increased beclin-1 expression above basal in tibial nerve, whereas it simply returned calpain and beclin-1 expression to their basal levels in spinal cord. In conclusion, the intoxication of TOCP was associated with a significant change of beclin-1 in hen nervous tissues, which suggested that disruption of autophagy-regulated machinery in neurons might be involved in the pathogenesis of OPIDN.

Semipreparative enantioseparation of methamidophos by HPLC-UV and preliminary in vitro study of butyrylcholinesterase inhibition

Many chiral pesticides are introduced into the environment as racemates, although their pesticidal activity is usually the result of preferential reactivity of only one enantiomer, while the other enantiomer may have toxic effects against nontarget organisms. Methamidophos (O,S-dimethyl phosphoramidothioate), a chiral compound, is an insecticide widely used in agriculture in both developed and developing countries. However, this pesticide has a high toxicity not only to targeted insects but also to human and animals. In the present study, the enantiomers of methamidophos were enantiomerically separated by a semipreparative chiral liquid chromatography at the multimilligram scale on a polysaccharide-based chiral stationary phase and a preliminary evaluation of their in vitro inhibition of plasma butyrylcholinesterase (BChE) of hens was performed. In the present study, our first effort was to resolve the racemic mixture of methamidophos and to that end reversed-phase, normal-phase, and polar organic elution conditions were investigated in four different polysaccharide-based chiral phases. The best performance was achieved on a cellulose tris(3,5-dimethylphenylcarbamate) phase under normal phase. This chromatographic condition allowed the separation of 225 mg of methamidophos enantiomers with a high degree of chiral purity (>98%) in a short analysis time. Significant differences were found between the concentration that causes 50% of enzyme inhibition (IC50) of the three isoforms of methamidophos. (-)-Methamidophos showed an IC50 approximately three times larger than the (+)-enantiomer for plasma BChE of hens.

Veterinary Pesticides

Veterinary pesticides are used to treat a range of parasitic conditions in companion and farm animals. These products are based on a number of different compounds with different modes of action and different spectra of toxicity. The older agents include the synthetic pyrethroids and organophosphorus compounds, while the newer examples include, for example, representatives of the insect growth promoters, the neonicotinoids, and the oxadiazones. For many of these compounds, toxicity is associated with their pharmacological activity or mode of action. Thus the synthetic pyrethroids and the organophosphorus compounds exert neurotoxic effects. For others, toxicity may be associated with mechanisms that are independent of their mode of action. When used according to the manufacturer's instructions, these products are generally safe and efficacious. However, accidental contamination and misuse can lead to toxicity in operators and treated animals. These compounds are important in the treatment of parasitic disease in animals and their regulation and uses are based on favourable risk-benefit outcomes.

Polyisoprenylation potentiates the inhibition of polyisoprenylated methylated protein methyl esterase and the cell degenerative effects of sulfonyl fluorides

The polyisoprenylation pathway incorporates a reversible step that metabolizes polyisoprenylated methylated proteins from the ester to the carboxylate form. Polyisoprenylated protein methyl transferase (PPMTase) catalyses the esterification whereas polyisoprenylated methylated protein methyl esterase (PMPMEase) hydrolyzes them. Significant changes in the balance between the two enzymes may alter polyisoprenylated protein function possibly resulting in disease. Previous studies show that PMPMEase is the serine hydrolase, Sus scrofa carboxylesterase. Its susceptibility to the nonspecific serine hydrolase inhibitor, phenylmethylsulfonyl fluoride (PMSF) paved the way for its use as a prototypical compound to design and synthesize a series of putative high affinity specific inhibitors of PMPMEase. Pseudo first-order kinetics revealed an over 680-fold increase in k(obs)/[I] values from PMSF (6 M(-1)-1s(-1)), S-phenyl (L-50, 180 M(-1)s(-1)), S-benzyl (L-51, 350 M(-1)s(-1)), S-trans, trans-farnesyl (L-28, 2000 M(-1)s(-1)), to S-trans-geranylated (L-23, 4100 M(-1)s(-1)) 2-thioethanesulfonyl fluorides. C10 S-alkyl substitution revealed a k(obs)/[I] value (1800 M(-1)s(-1)) that was 298 times greater than that for PMSF. The compounds induced the degeneration of human neuroblastoma SH-SY5Y cells with EC(50) values of 49, 130 and >1000 µM for L-28, L-23 and PMSF, respectively. The increased affinity with the polyisoprenyl derivatization is consistent with the observed substrate specificity and the reported hydrophobic nature of the active site. These results suggest that (1) PMPMEase is a key enzyme for polyisoprenylated protein metabolism, (2) regulation of its activity is essential for maintaining normal cell viability, (3) abnormal activities may be involved in degenerative diseases and cancers and (4) its specific inhibitors may be useful in combating cancers.

Characterization of tunable piperidine and piperazine carbamates as inhibitors of endocannabinoid hydrolases

Monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) are two enzymes from the serine hydrolase superfamily that degrade the endocannabinoids 2-arachidonoylglycerol and anandamide, respectively. We have recently discovered that MAGL and FAAH are both inhibited by carbamates bearing an N-piperidine/piperazine group. Piperidine/piperazine carbamates show excellent in vivo activity, raising brain endocannabinoid levels and producing CB1-dependent behavioral effects in mice, suggesting that they represent a promising class of inhibitors for studying the endogenous functions of MAGL and FAAH. Herein, we disclose a full account of the syntheses, structure-activity relationships, and inhibitory activities of piperidine/piperazine carbamates against members of the serine hydrolase family. These scaffolds can be tuned for MAGL-selective or dual MAGL-FAAH inhibition by the attachment of an appropriately substituted bisarylcarbinol or aryloxybenzyl moiety, respectively, on the piperidine/piperazine ring. Modifications to the piperidine/piperazine ring ablated inhibitory activity, suggesting a strict requirement for a six-membered ring to maintain potency.

Dual blockade of FAAH and MAGL identifies behavioral processes regulated by endocannabinoid crosstalk in vivo

Delta(9)-tetrahydrocannabinol (THC), the psychoactive component of marijuana, and other direct cannabinoid receptor (CB1) agonists produce a number of neurobehavioral effects in mammals that range from the beneficial (analgesia) to the untoward (abuse potential). Why, however, this full spectrum of activities is not observed upon pharmacological inhibition or genetic deletion of either fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL), enzymes that regulate the two major endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG), respectively, has remained unclear. Here, we describe a selective and efficacious dual FAAH/MAGL inhibitor, JZL195, and show that this agent exhibits broad activity in the tetrad test for CB1 agonism, causing analgesia, hypomotilty, and catalepsy. Comparison of JZL195 to specific FAAH and MAGL inhibitors identified behavioral processes that were regulated by a single endocannabinoid pathway (e.g., hypomotility by the 2-AG/MAGL pathway) and, interestingly, those where disruption of both FAAH and MAGL produced additive effects that were reversed by a CB1 antagonist. Falling into this latter category was drug discrimination behavior, where dual FAAH/MAGL blockade, but not disruption of either FAAH or MAGL alone, produced THC-like responses that were reversed by a CB1 antagonist. These data indicate that AEA and 2-AG signaling pathways interact to regulate specific behavioral processes in vivo, including those relevant to drug abuse, thus providing a potential mechanistic basis for the distinct pharmacological profiles of direct CB1 agonists and inhibitors of individual endocannabinoid degradative enzymes.

Nanotechnology-based electrochemical sensors for biomonitoring chemical exposures

The coupling of dosimetry measurements and modeling represents a promising strategy for deciphering the relationship between chemical exposure and disease outcome. To support the development and implementation of biological monitoring programs, quantitative technologies for measuring xenobiotic exposure are needed. The development of portable nanotechnology-based electrochemical (EC) sensors has the potential to meet the needs for low cost, rapid, high-throughput, and ultrasensitive detectors for biomonitoring an array of chemical markers. Highly selective EC sensors capable of pM sensitivity, high-throughput and low sample requirements (<50 microl) are discussed. These portable analytical systems have many advantages over currently available technologies, thus potentially representing the next generation of biomonitoring analyzers. This paper highlights research focused on the development of field-deployable analytical instruments based on EC detection. Background information and a general overview of EC detection methods and integrated use of nanomaterials in the development of these sensors are provided. New developments in EC sensors using various types of screen-printed electrodes, integrated nanomaterials, and immunoassays are presented. Recent applications of EC sensors for assessing exposure to pesticides or detecting biomarkers of disease are highlighted to demonstrate the ability to monitor chemical metabolites, enzyme activity, or protein biomarkers of disease. In addition, future considerations and opportunities for advancing the use of EC platforms for dosimetric studies are discussed.

Potential developmental neurotoxicity of pesticides used in Europe

Pesticides used in agriculture are designed to protect crops against unwanted species, such as weeds, insects, and fungus. Many compounds target the nervous system of insect pests. Because of the similarity in brain biochemistry, such pesticides may also be neurotoxic to humans. Concerns have been raised that the developing brain may be particularly vulnerable to adverse effects of neurotoxic pesticides. Current requirements for safety testing do not include developmental neurotoxicity. We therefore undertook a systematic evaluation of published evidence on neurotoxicity of pesticides in current use, with specific emphasis on risks during early development. Epidemiologic studies show associations with neurodevelopmental deficits, but mainly deal with mixed exposures to pesticides. Laboratory experimental studies using model compounds suggest that many pesticides currently used in Europe--including organophosphates, carbamates, pyrethroids, ethylenebisdithiocarbamates, and chlorophenoxy herbicides--can cause neurodevelopmental toxicity. Adverse effects on brain development can be severe and irreversible. Prevention should therefore be a public health priority. The occurrence of residues in food and other types of human exposures should be prevented with regard to the pesticide groups that are known to be neurotoxic. For other substances, given their widespread use and the unique vulnerability of the developing brain, the general lack of data on developmental neurotoxicity calls for investment in targeted research. While awaiting more definite evidence, existing uncertainties should be considered in light of the need for precautionary action to protect brain development.

Nanoparticle-based electrochemical immunosensor for the detection of phosphorylated acetylcholinesterase: an exposure biomarker of organophosphate pesticides and nerve agents

A nanoparticle-based electrochemical immunosensor has been developed for the detection of phosphorylated acetylcholinesterase (AChE), which is a potential biomarker of exposure to organophosphate (OP) pesticides and chemical warfare nerve agents. Zirconia nanoparticles (ZrO(2) NPs) were used as selective sorbents to capture the phosphorylated AChE adduct, and quantum dots (ZnS@CdS, QDs) were used as tags to label monoclonal anti-AChE antibody to quantify the immunorecognition events. The sandwich-like immunoreactions were performed among the ZrO(2) NPs, which were pre-coated on a screen printed electrode (SPE) by electrodeposition, phosphorylated AChE and QD-anti-AChE. The captured QD tags were determined on the SPE by electrochemical stripping analysis of its metallic component (cadmium) after an acid-dissolution step. Paraoxon was used as the model OP insecticide to prepare the phosphorylated AChE adducts to demonstrate proof of principle for the sensor. The phosphorylated AChE adduct was characterized by Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy. The binding affinity of anti-AChE to the phosphorylated AChE was validated with an enzyme-linked immunosorbent assay. The parameters (e.g., amount of ZrO(2) NP, QD-anti-AChE concentration,) that govern the electrochemical response of immunosensors were optimized. The voltammetric response of the immunosensor is highly linear over the range of 10 pM to 4 nM phosphorylated AChE, and the limit of detection is estimated to be 8.0 pM. The immunosensor also successfully detected phosphorylated AChE in human plasma. This new nanoparticle-based electrochemical immunosensor provides an opportunity to develop field-deployable, sensitive, and quantitative biosensors for monitoring exposure to a variety of OP pesticides and nerve agents.

Determination of airborne trialkyl and triaryl organophosphates originating from hydraulic fluids by gas chromatography–mass spectrometry

Methodology for personal occupational exposure assessment of airborne trialkyl and triaryl organophosphates originating from hydraulic fluids by active combined aerosol and vapor sampling at 1.5L/min is presented. Determination of the organophosphates was performed by gas chromatography-mass spectrometry. Combinations of adsorbents (Anasorb 747, Anasorb CSC, Chromosorb 106, XAD-2 and silica gel) with an upstream cassette with glass fiber or PTFE filters and different desorption/extraction solvents (CS(2), CS(2)-dimethylformamide (50:1, v/v), toluene, dichloromethane, methyl-t-butyl ether and methanol) have been evaluated for optimized combined vapor and aerosol air sampling of the organophosphates tri-isobutyl, tri-n-butyl, triphenyl, tri-o-cresyl, tri-m-cresyl and tri-p-cresyl phosphates. The combination of Chromosorb 106 and 37 mm filter cassette with glass fiber filter and dichloromethane as desorption/extraction solvent was the best combination for mixed phase air sampling of the organophosphates originating from hydraulic fluids. The triaryl phosphates were recovered solely from the filter, while the trialkyl phosphates were recovered from both the filter and the adsorbent. The total sampling efficiency on the combined sampler was in the range 92-101% for the studied organophosphates based on spiking experiments followed by pulling air through the sampler. Recoveries after 28 days storage were 98-102% and 99-101% when stored at 5 and -20 degrees C, respectively. The methodology was further evaluated in an exposure chamber with generated oil aerosol atmospheres with both synthetic and mineral base oils with added organophosphates in various concentrations, yielding total sampling efficiencies in close comparison to the spiking experiments. The applicability of the method was demonstrated by exposure measurements in a mechanical workshop where system suitability tests are performed on different aircraft components in a test bench, displaying tricresyl phosphate air concentrations of 0.024 and 0.28 mg/m(3), as well as during aircraft maintenance displaying tri-n-butyl phosphate air concentrations of 0.061 and 0.072 mg/m(3).

Diagnostic aspects of organophosphate poisoning

Organophosphate (OP)-type chemical warfare agents (nerve agents) present a constant threat to the population. Sensitive and specific methods for the detection and verification of exposure to nerve agents are required for diagnosis, therapeutic monitoring, health surveillance and forensic purposes. Determination of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity in blood remains a mainstay for the fast initial screening but lacks sensitivity and specificity. Quantitative analysis of nerve agents and their degradation products in plasma and urine by mass spectrometric methods may prove exposure but is limited to hours or days after the incident due to the short residence time of the analytes. Investigation of protein adducts extends the time interval between exposure and sampling and may be suitable to detect low-level exposure. Definitive prove of exposure requires a spectrum of different methods, expensive and sophisticated equipment and will be limited to specialized laboratories.

Veterinary pharmacovigilance. Part 4. Adverse reactions in humans to veterinary medicinal products

Although seemingly rare, adverse reactions to veterinary products do occur. These may arise from inadvertent exposure during use or as a result of occupational accidents. They are often mild in nature and include adverse effects such as minor skin reactions. However, more serious reactions may occur, and they are not restricted to the effects of the veterinary medicines themselves. For example, high-pressure injection injuries may occur as a result of accidents occurring during animal vaccination operations. This paper reviews some of these events, mentions where appropriate the regulatory actions taken, and describes some of the measures used to minimise such effects in the future, and serves to bring the issues discussed here to the attention of pharmacologists, pharmacoepidemiologists and others who train those who use veterinary medicinal products.

Organophosphates/nerve agent poisoning: mechanism of action, diagnosis, prophylaxis, and treatment

OP/nerve agents are still considered as important chemicals acting on living organisms and are widely used. They are characterized according to their action as compounds influencing cholinergic nerve transmission via inhibition of AChE. Modeling of this action and extrapolation of experimental data from animals to humans is more possible for highly toxic agents than for the OP. The symptoms of intoxication comprise nicotinic, muscarinic, and central symptoms; for some OP/nerve agents, a delayed neurotoxicity is observed. Cholinesterases (AChE and BuChE) are characterized as the main enzymes involved in the toxic effect of these compounds, including molecular forms. The activity of both enzymes (and molecular forms) is influenced by inhibitors (reversible, irreversible, and allosteric) and other factors, such as pathological states. There are different methods for cholinesterase determination; however, the most frequent is the method based on the hydrolysis of thiocholine esters and subsequent detection of free SH-group of the released thiocholine. The diagnosis of OP/nerve agent poisoning is based on anamnesis, the clinical status of the intoxicated organism, and on cholinesterase determination in the blood. For nerve agent intoxication, AChE in the red blood cell is more diagnostically important than BuChE activity in the plasma. This enzyme is a good diagnostic marker for intoxication with OP pesticides. Some other biochemical examinations are recommended, especially arterial blood gas, blood pH, minerals, and some other specialized parameters usually not available in all clinical laboratories. These special examinations are important for prognosis of the intoxication, for effective treatment, and for retrospective analysis of the agent used for exposure. Some principles of prophylaxis against OP/nerve agent poisoning comprising the administration of reversible cholinesterase inhibitors such as pyridostigmine (alone or in combination with other drugs), scavengers such as preparations of cholinesterases, some therapeutic drugs, and possible combinations are given. Basic principles of the treatment of nerve agent OP poisoning are described. They are based on the administration of anticholinergics (mostly atropine but some other anticholinergics can be recommended) as a symptomatic treatment, cholinesterase reactivators as a causal treatment (different types but without a universal reactivator against all OP/nerve agents) as the first aid and medical treatment, and anticonvulsants, preferably diazepam though some other effective benzodiazepines are available. New drugs for the treatment are under experimental study based on new approaches to the mechanism of action. Future trends in the complex research of these compounds, which is important not only for the treatment of intoxication but also for the quantitative and qualitative increase of our knowledge of toxicology, neurochemistry, neuropharmacology, clinical biochemistry, and analytical chemistry in general, are characterized.

Brain-specific deletion of neuropathy target esterase/swisscheese results in neurodegeneration

Neuropathy target esterase (NTE) is a neuronal membrane protein originally identified for its property to be modified by organo-phosphates (OPs), which in humans cause neuropathy characterized by axonal degeneration. Drosophila mutants for the homolog gene of NTE, swisscheese (sws), indicated a possible involvement of sws in the regulation of axon-glial cell interaction during glial wrapping. However, the role of NTE/sws in mammalian brain pathophysiology remains unknown. To investigate NTE function in vivo, we used the cre/loxP site-specific recombination strategy to generate mice with a specific deletion of NTE in neuronal tissues. Here we show that loss of NTE leads to prominent neuronal pathology in the hippocampus and thalamus and also defects in the cerebellum. Absence of NTE resulted in disruption of the endoplasmic reticulum, vacuolation of nerve cell bodies, and abnormal reticular aggregates. Thus, these results identify a physiological role for NTE in the nervous system and indicate that a loss-of-function mechanism may contribute to neurodegenerative diseases characterized by vacuolation and neuronal loss.

Quantitative structure-activity relationships predict the delayed neurotoxicity potential of a series of O-alkyl-O-methylchloroformimino phenylphosphonates

Inhibition of acetylcholinesterase (AChE) versus inhibition and aging of neuropathy target esterase (NTE) by organophosphorus (OP) compounds in vivo can give rise to distinct neurological consequences: acute cholinergic toxicity versus OP compound-induced delayed neurotoxicity (OPIDN). Previous work has shown that the relative potency of an OP compound to react with NTE versus AChE in vitro may predict its capability to produce OPIDN. The present study was conducted to evaluate further the validity of such predictions and to enhance them with quantitative structure-activity relationships (QSAR) using a homologous series of alkyl phenylphosphonates (RO)C6H5P(O)ON = CCICH3 (PhP; R = alkyl). Neuropathic potential of PhP was assessed by measuring ki(NTE)ki(AChE) ratios in vitro and comparing these with ED50 ratios in vivo. Selectivity for NTE increased with rising R-group hydrophobicity. The ki(NTE)/ki(AChE) ratios were 0.42 (methyl), 3.6 (ethyl), 15 (isopropyl), 36 (propyl), 69 (isobutyl), 105 (butyl), and 124 (pentyl). Ratios > 1 suggest the potential to produce OPIDN at doses lower than the LD50. Inhibition of NTE and AChE in hen brain in vivo was studied 24 h after i.m. injection of hens with increasing doses of methyl and butyl derivatives. Analysis of dose-response curves yielded ED50(AChE)/ED50(NTE) ratio of 0.86 for methyl PhP and 22.1 for butyl PhP. These results predict that the butyl derivative should be more neuropathic than the methyl analogue. Excellent correspondence between in vivo and in vitro predictions of neuropathic potential indicate that valid predictive QSAR models may be based on the in vitro approach. Adoption of this system would result in reducing experimental animal use, lowering costs, accelerating data production, and enabling standardization of a biochemically based risk assessment of the neuropathic potential of OP compounds.

Correlation of binding sites for diisopropyl phosphorofluoridate with cholinesterase and neuropathy target esterase in membrane and cytosol preparations from hen

To find new putative target(s) for organophosphorus induced delayed neurotoxicity (OPIDN), we investigated the biochemical and pharmacological characteristics of [3H] diisopropyl phosphorofluoridate (DFP) binding to membrane and cytosol preparations from the brain and spinal cord of hens. Specific [3H]DFP binding was determined by subtracting non-specific binding from total binding. The binding sites of [3H]DFP, an organophosphate that induces OPIDN, were found not only on membrane but also in cytosol. Reduction of subsequent ex vivo specific [3H]DFP binding by in vivo pretreatment with unlabeled DFP was found in cytosol, not membrane. The reduced binding lasted to the onset of OPIDN, especially in spinal cord. These results suggest that the specific DFP binding sites in cytosol, rather than on membrane, are the most important with regard to the initiation of OPIDN. Inhibitors of cholinesterase (ChE) and neuropathy target esterase (NTE) other than DFP did not affect specific [3H]DFP binding to either membranes or cytosol in vivo. Additionally, inhibition of the activities of these esterases by these compounds was not consistent with either the degree of inhibition of the [3H]DFP binding or a time-dependent manner of OPIDN. These results suggest that DFP binding site(s) involved in the initiation of OPIDN may be different from the active sites of ChE and NTE.

Distal sensory axonopathy after sarin intoxication

A 51-year-old man inhaled sarin during a terrorist attack on the Tokyo subway system and died 15 months later. Neuropathologic examination revealed marked nerve fiber decrease in the sural nerve, moderate nerve fiber loss in the sciatic nerve, and unremarkable dorsal root ganglia, dorsal roots, and posterior column of the spinal cord. This pathology is consistent with dying-back degeneration of the peripheral nervous system and could represent a late sequela of sarin intoxication.

Delayed neuropathy and inhibition of soluble neuropathy target esterase following the administration of organophosphorus compounds to hens

Delayed neuropathy and inhibition of soluble neuropathy target esterase (NTE) and acetylcholinesterase (AChE) activities in different regions of brain and spinal cord of adult hens were studied after the intravenous administration of leptophos (30 mg/kg), tri-o-cresyl phosphate (TOCP 40 mg/kg) or dipterex (200 mg/kg). The level of NTE activity varied according to the regions of the central nervous system (CNS) of the control (normal) hen, being higher in the cerebrum (74.1 micromol of phenyl valerate hydrolyzed/10 minutes/mg protein) and in the cerebellum (68.7), and lower in the spinal cord (44.5 in cervical, 55.6 in thoracic and 50.0 in lumbar cord). Hens given leptophos and TOCP demonstrated delayed neuropathy with obvious inhibition of NTE, but the times of onset and the degrees of peak inhibition of NTE activity were different: 6-24 hours after dosing and 73-82% of normal activity for leptophos, and 24-48 hours and 45-80% for TOCP, respectively. Furthermore, the average inhibition of NTE during 6-48 hours after dosing, (called here 'period average inhibition') was also significantly different between the leptophos group (63-73%) and TOCP group (40-64%). Hens given dipterex did not demonstrate delayed neuropathy, and had the least peak inhibition and period average inhibition of NTE activity among the 3 groups. Ratios of NTE inhibition/AChE inhibition were higher in the leptophos group (0.91-1.24) and TOCP group (1.13-2.45) than in the dipterex group (0.25-0.79). These results indicate that the distribution of NTE in the soluble fraction of membrane proteins is different in different regions of the CNS, and that the degree of peak inhibition of NTE activity and the time of onset of peak inhibition induced by organophosphorus compounds (OPs) also differ for different OPs. Thus, practical and useful NTE measurements should identify the peak inhibition and period inhibition in several nervous tissue regions.

Actions of two highly potent organophosphorus neuropathy target esterase inhibitors in mammalian cell lines

Neuropathy target esterase (NTE) is inhibited by many organophosphorus compounds that induce delayed neuropathy. This study examines two of the most potent NTE inhibitors, 2-octyl-4H-1,3,2-benzodioxaphosphorin 2-oxide (OBDPO) and ethyl octylphosphonofluoridate (EOPF), in cell lines with neural properties (PC-12 and NB41A3) and of nonneural origin (C6 and HeLa). NTE-like esteratic activity is higher in PC-12, HeLa and C6 cells than in NB41A3 cells and in each case is inhibited 50% by OBDPO and EOPF at 0.03-3.4 nM in vitro and by OBDPO at 0.080-36 nM in situ in culture. An NTE-like protein(s) of about 155 kDa is phosphorylated and labeled by [3H-octyl]OBDPO in these cell lines in the same order as their relative NTE esteratic activity. Cytotoxic levels of OBDPO and EOPF (300-500 microM) are generally 10(5) to > 10(7)-fold higher than required for NTE inhibition. PC-12 cells and OBDPO/[3H]OBDPO and EOPF are therefore suitable for research on non-lethal biochemical disruptions from NTE phosphorylation and aging.