Large-scale purification and long-term stability of human butyrylcholinesterase: a potential bioscavenger drug

Optical imaging probes for selective detection of butyrylcholinesterase

Butyrylcholinesterase (BChE), a member of the human serine hydrolase family, is an essential enzyme for cholinergic neurotransmission as it catalyzes the hydrolysis of acetylcholine. It also plays central roles in apoptosis, lipid metabolism, and xenobiotic detoxification. On the other side, abnormal levels of BChE are directly associated with the formation of pathogenic states such as neurodegenerative diseases, psychiatric and cardiovascular disorders, liver damage, diabetes, and cancer. Thus, selective and sensitive detection of BChE level in living organisms is highly crucial and is of great importance to further understand the roles of BChE in both physiological and pathological processes. However, it is a very complicated task due to the potential interference of acetylcholinesterase (AChE), the other human cholinesterase, as these two enzymes share a very similar substrate scope. To this end, optical imaging probes have attracted immense attention in recent years as they have modular structures, which can be tuned precisely to satisfy high selectivity toward BChE, and at the same time they offer real time and nondestructive imaging opportunities with a high spatial and temporal resolution. Here, we summarize BChE selective imaging probes by discussing the critical milestones achieved during the development process of these molecular sensors over the years. We put a special emphasis on design principles and biological applications of highly promising new generation activity-based probes. We also give a comprehensive outlook for the future of BChE-responsive probes and highlight the ongoing challenges. This collection marks the first review article on BChE-responsive imaging agents.

Kinetic and structural studies on the inhibition of acetylcholinesterase and butyrylcholinesterase by a series of multitarget-directed galantamine-peptide derivatives

Complex neurological disorders, including Alzheimer's disease, are one of the major therapeutic areas to which multitarget drug discovery strategies have been applied in the last twenty years. Due to the complex multifactorial etiopathogenesis of Alzheimer's disease, it has been proposed that to be successful the pharmaceutical agents should act on multiple targets in order to restore the complex disease network and to provide disease modifying effects. Here we report on the synthesis and the anticholinergic activity profiles of seven multitarget anti-Alzheimer compounds designed by combining galantamine, a well-known acetylcholinesterase inhibitor, with different peptide fragments endowed with inhibitory activity against BACE-1. A complementary approach based on molecular docking simulations of the galantamine-peptide derivatives in the active sites of acetylcholinesterase and of the related butyrylcholinesterase, as well as on inhibition kinetics, by global fitting of the reaction progress curves, allowed to gain insights into the enzyme-inhibitor mechanism of interaction. The resulting structure-activity relationships pave the way towards the design of more effective pharmacodynamic/pharmacokinetic multitarget inhibitors.

Poisoning by organophosphorus nerve agents and pesticides: An overview of the principle strategies and current progress of mass spectrometry-based procedures for verification

•

Evidence of poisoning with organophosphorus (OP) nerve agents requires biomedical verification.

•

OP nerve agents undergo common biotransformation pathways producing valuable biomarkers.

•

Internationally accepted methods target remaining poison, hydrolysis products and protein-adducts.

•

Mass spectrometry-based methods provide optimum selectivity and sensitivity for identification.

•

Methods, strategies, current proceedings, quality criteria and real cases of poisoning are presented.

Intoxication by organophosphorus (OP) poisons, like nerve agents and pesticides, is characterized by the life-threatening inhibition of acetylcholinesterase (AChE) caused by covalent reaction with the serine residue of the active site of the enzyme (phosphylation). Similar reactions occur with butyrylcholinesterase (BChE) and serum albumin present in blood as dissolved proteins. For forensic purposes, products (adducts) with the latter proteins are highly valuable long-lived biomarkers of exposure to OP agents that are accessible by diverse mass spectrometric procedures. In addition, the evidence of poison incorporation might also succeed by the detection of remaining traces of the agent itself, but more likely its hydrolysis and/or enzymatic degradation products. These relatively short-lived molecules are distributed in blood and tissue, and excreted via urine. This review presents the mass spectrometry-based methods targeting the different groups of biomarkers in biological samples, which are already internationally accepted by the Organisation for the Prohibition of Chemical Weapons (OPCW), introduces novel approaches in the field of biomedical verification, and outlines the strict quality criteria that must be fulfilled for unambiguous forensic analysis.

Acetylcholinesterase inhibition resulting from exposure to inhaled OP can be prevented by pretreatment with BChE in both macaques and minipigs

More frequent and widespread nerve agent attacks highlight the need for efficacious pre- and post-exposure organophosphate (OP) counter-measures to protect military and civilian populations. Because of critical targeting of acetylcholinesterase (AChE) in the CNS by OPs, a pre-treatment candidate for preventing/reducing poisoning will be a broadly acting molecule that scavenges OPs in blood before they reach their physiological targets. Prophylactic human butyrylcholinesterase (HuBChE), the leading pretreatment candidate, has been shown to protect against multiple LD50's of nerve agents in rodents, macaques, and minipigs. This review describes the development of a HuBChE bioscavenger pretreatment from early proof-of-concept studies to pre-clinical studies with the native injectable enzyme and the development of aerosolized forms of recombinant enzyme, which can be delivered by inhalation nebulizer devices, to effect protection against inhaled OP nerve agents and insecticides. Early animal studies utilized parenteral exposure. However, lungs are the portal of entry for most volatile OP vapors and represent the major means of OP intoxication. In this regard, pretreat-ment with 7.5 mg/kg of HuBChE by IM injection protected minipigs against lethal sarin vapor and prevented AChE inhibition in the blood. This is similar to the five-day protection in macaques by an aerosolized rHuBChE using a nebulizer against aerosolized paraoxon (estimated to be an 8 mg/kg estimated human dose). Importantly, lethal inhaled doses of OP may be smaller relative to the same dose delivered by injection, thus reducing the protective HuBChE dose, while a combination of HuBChE and post-exposure oxime may prolong protection.

Monoclonal antibodies to fetal bovine serum acetylcholinesterase distinguish between acetylcholinesterases from ruminant and non-ruminant species

Two types of cholinesterases (ChEs) are present in mammalian blood and tissues: acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). While AChE regulates neurotransmission by hydrolyzing acetylcholine at the postsynaptic membranes and neuromuscular junctions, BChE in plasma has been suggested to be involved in detoxifying toxic compounds. This study was undertaken to establish the identity of circulating ChE activity in plasmas from domestic animals (bovine, ovine, caprine, porcine and equine) by assessing sensitivity to AChE-specific inhibitors (BW284c51 and edrophonium) and BChE-specific inhibitors (dibucaine, ethopropazine and Iso-OMPA) as well as binding to anti-FBS AChE monoclonal antibodies (MAbs). Based on the inhibition of ChE activity by ChE-specific inhibitors, it was determined that bovine, ovine and caprine plasma predominantly contain AChE, while porcine and equine plasma contain BChE. Three of the anti-FBS AChE MAbs, 4E5, 5E8 and 6H9, inhibited 85-98% of enzyme activity in bovine, ovine and caprine plasma, confirming that the esterase in these plasmas was AChE. These MAbs did not bind to purified recombinant human or mouse AChE, demonstrating that these MAbs were specific for AChEs from ruminant species. These MAbs did not inhibit the activity of purified human BChE, or ChE activity in porcine and equine plasma, confirming that the ChE in these plasmas was BChE. Taken together, these results demonstrate that anti-FBS AChE MAbs can serve as useful tools for distinguishing between AChEs from ruminant and non-ruminant species and BChEs.

Tuning Butyrylcholinesterase Inactivation and Reactivation by Polymer-Based Protein Engineering

Organophosphate nerve agents rapidly inhibit cholinesterases thereby destroying the ability to sustain life. Strong nucleophiles, such as oximes, have been used as therapeutic reactivators of cholinesterase-organophosphate complexes, but suffer from short half-lives and limited efficacy across the broad spectrum of organophosphate nerve agents. Cholinesterases have been used as long-lived therapeutic bioscavengers for unreacted organophosphates with limited success because they react with organophosphate nerve agents with one-to-one stoichiometries. The chemical power of nucleophilic reactivators is coupled to long-lived bioscavengers by designing and synthesizing cholinesterase-polymer-oxime conjugates using atom transfer radical polymerization and azide-alkyne "click" chemistry. Detailed kinetic studies show that butyrylcholinesterase-polymer-oxime activity is dependent on the electrostatic properties of the polymers and the amount of oxime within the conjugate. The covalent coupling of oxime-containing polymers to the surface of butyrylcholinesterase slows the rate of inactivation of paraoxon, a model nerve agent. Furthermore, when the enzyme is covalently inhibited by paraoxon, the covalently attached oxime induced inter- and intramolecular reactivation. Intramolecular reactivation will open the door to the generation of a new class of nerve agent scavengers that couple the speed and selectivity of biology to the ruggedness and simplicity of synthetic chemicals.

Purification of human butyrylcholinesterase from frozen Cohn fraction IV-4 by ion exchange and Hupresin affinity chromatography

Human butyrylcholinesterase (HuBChE) is being developed as a therapeutic for protection from the toxicity of nerve agents. An enriched source of HuBChE is Cohn fraction IV-4 from pooled human plasma. For the past 40 years, purification of HuBChE has included affinity chromatography on procainamide-Sepharose. The present report supports a new affinity sorbent, Hupresin, for purification of HuBChE from Cohn fraction IV-4. Nine batches of 70–80 kg frozen Cohn fraction were extracted with water, filtered, and chromatographed on 30 L of Q-Ceramic ion exchange sorbent at pH 4.5. The 4% pure Q-eluent was pumped onto 4.2 L Hupresin, where contaminants were washed off with 0.3 M NaCl in 20 mM sodium phosphate pH 8.0, before 99% pure HuBChE was eluted with 0.1 M tetramethylammonium bromide. The average yield was 1.5 g of HuBChE from 80 kg Cohn paste. Recovery of HuBChE was reduced by 90% when the paste was stored at -20°C for 1 year, and reduced 100% when stored at 4°C for 24h. No reduction in HuBChE recovery occurred when paste was stored at -80°C for 3 months or 3 years. Hupresin and procainamide-Sepharose were equally effective at purifying HuBChE from Cohn fraction. HuBChE in Cohn fraction required 1000-fold purification to attain 99% purity, but 15,000-fold purification when the starting material was plasma. HuBChE (P06276) purified from Cohn fraction was a 340 kDa tetramer of 4 identical N-glycated subunits, stable for years in solution or as a lyophilized product.

Gas chromatography-mass spectrometry with spiral large-volume injection for determination of fluoridated phosphonates produced by fluoride-mediated regeneration of nerve agent adduct in human serum

A sensitive method for determination of fluoridated phosphonates produced by fluoride-mediated regeneration of nerve agent adduct in human serum was developed using gas chromatography-mass spectrometry (GCMS) with large-volume injection. The GC injection was administered using stomach-type spiral injector (LVI, AiSTI SCIENCE) enabling introduction of only target compounds from 50 μL ethyl acetate extract after purging the solvent. For GCMS analysis of sarin (GB), 670 times higher sensitivity, based on limit of detection (LOD, S/N = 3, on extracted ion chromatogram (EIC) at m/z 99), was achieved using this injection (50 μL) compared to that achieved using 1 μL split injection (ratio 20:1). Ethyl (EtGB), isopropyl (GB), n-propyl (nPrGB), isobutyl (iBuGB), pinacolyl (GD), cyclohexyl (GF) methylphosphonofluoridates, and O-ethyl N, N-dimethylphosphoramidofluoridate (GAF) were detected with low LOD (15-75 pg/mL) and sharp peak shapes (high practical plate number (defined as 5.54 x (t_R/W_h)², where t_R is the retention time and W_h is the bandwidth at half-height): 1100000-2400000) in GCMS using a polar separation column, electron ionization, and quadruple mass analyzer. During the analysis of fluoridated phosphonate-spiked ethyl acetate extract of solid phase extraction (SPE, Bond Elut NEXUS) from fluoride-mediated regeneration of blank human plasma, LOD (on EIC at m/z 99 except for GAF (m/z 126)) were 25-140 pg/mL with sharp peak shapes. The reaction recoveries in fluoride-mediated regeneration of plasma, which was inhibited by GB, GD, GA, GF, VX, and Russian VX (10 ng/mL), were 49-114% except for GD (10%). The concentration levels of 0.3-1 ng/mL of nerve agents in plasma could be determined.

Purification of recombinant human butyrylcholinesterase on Hupresin®

Affinity chromatography on procainamide-Sepharose has been an important step in the purification of butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) since its introduction in 1978. The procainamide affinity gel has limitations. In the present report a new affinity gel called Hupresin® was evaluated for its ability to purify truncated, recombinant human butyrylcholinesterase (rHuBChE) expressed in a stably transfected Chinese Hamster Ovary cell line. We present a detailed example of the purification of rHuBChE secreted into 3940 mL of serum-free culture medium. The starting material contained 13,163 units of BChE activity (20.9 mg). rHuBChE was purified to homogeneity in a single step by passage over 82 mL of Hupresin® eluted with 0.1 M tetramethylammonium bromide in 20 mM TrisCl pH 7.5. The fraction with the highest specific activity of 630 units/mg contained 11 mg of BChE. Hupresin® is superior to procainamide-Sepharose for purification of BChE, but is not suitable for purifying native AChE because Hupresin® binds AChE so tightly that AChE is not released with buffers, but is desorbed with denaturing solvents such as 50% acetonitrile or 1% trifluoroacetic acid. Procainamide-Sepharose will continue to be useful for purification of AChE.

Purification, characterization, and N-glycosylation of recombinant butyrylcholinesterase from transgenic rice cell suspension cultures

Recombinant butyrylcholinesterase produced in a metabolically regulated transgenic rice cell culture (rrBChE) was purified to produce a highly pure (95%), active form of enzyme. The developed downstream process uses common manufacturing friendly operations including tangential flow filtration, anion-exchange chromatography, and affinity chromatography to obtain a process recovery of 42% active rrBChE. The purified rrBChE was then characterized to confirm its comparability to the native human form of the molecule (hBChE). The recombinant and native enzyme demonstrated comparable enzymatic behavior and had an identical amino acid sequence. However, rrBChE differs in that it contains plant-type complex N-glycans, including an α-1,3 linked core fucose, and a β-1,2 xylose, and lacking a terminal sialic acid. Despite this difference, rrBChE is demonstrated to be an effective stoichiometric bioscavenger for five different organophosphorous nerve agents in vitro. Together, the efficient downstream processing scheme and functionality of rrBChE confirm its promise as a cost-effective alternative to hBChE for prophylactic and therapeutic use.

Immunopurification of Acetylcholinesterase from Red Blood Cells for Detection of Nerve Agent Exposure

Nerve agents and organophosphorus pesticides make a covalent bond with the active site serine of acetylcholinesterase (AChE), resulting in inhibition of AChE activity and toxic symptoms. AChE in red blood cells (RBCs) serves as a surrogate for AChE in the nervous system. Mass spectrometry analysis of adducts on RBC AChE could provide evidence of exposure. Our goal was to develop a method of immunopurifying human RBC AChE in quantities adequate for detecting exposure by mass spectrometry. For this purpose, we immobilized 3 commercially available anti-human acetylcholinesterase monoclonal antibodies (AE-1, AE-2, and HR2) plus 3 new monoclonal antibodies. The monoclonal antibodies were characterized for binding affinity, epitope mapping by pairing analysis, and nucleotide and amino acid sequences. AChE was solubilized from frozen RBCs with 1% (v/v) Triton X-100. A 16 mL sample containing 5.8 μg of RBC AChE was treated with a quantity of soman model compound that inhibited 50% of the AChE activity. Native and soman-inhibited RBC AChE samples were immunopurified on antibody–Sepharose beads. The immunopurified RBC AChE was digested with pepsin and analyzed by liquid chromatography tandem mass spectrometry on a 6600 Triple-TOF mass spectrometer. The aged soman-modified PheGlyGluSerAlaGlyAlaAlaSer (FGESAGAAS) peptide was detected using a targeted analysis method. It was concluded that all 6 monoclonal antibodies could be used to immunopurify RBC AChE and that exposure to nerve agents could be detected as adducts on the active site serine of RBC AChE.

Characterization of butyrylcholinesterase in bovine serum

Human butyrylcholinesterase (HuBChE) protects from nerve agent toxicity. Our goal was to determine whether bovine serum could be used as a source of BChE. Bovine BChE (BoBChE) was immunopurified from 100 mL fetal bovine serum (FBS) or 380 mL adult bovine serum by binding to immobilized monoclonal mAb2. Bound proteins were digested with trypsin and analyzed by liquid chromatography-tandem mass spectrometry. The results proved that FBS and adult bovine serum contain BoBChE. The concentration of BoBChE was estimated to be 0.04 μg/mL in FBS, and 0.03 μg/mL in adult bovine serum, values lower than the 4 μg/mL BChE in human serum. Nondenaturing gel electrophoresis showed that monoclonal mAb2 bound BoBChE but not bovine acetylcholinesterase (BoAChE) and confirmed that FBS contains BoBChE and BoAChE. Recombinant bovine BChE (rBoBChE) expressed in serum-free culture medium spontaneously reactivated from inhibition by chlorpyrifos oxon at a rate of 0.0023 min^-1 (t_1/2 = 301 min^-1) and aged at a rate of 0.0138 min^-1 (t_1/2 = 50 min^-1). Both BoBChE and HuBChE have 574 amino acids per subunit and 90% sequence identity. However, the apparent size of serum BoBChE and rBoBChE tetramers was much greater than the 340,000 Da of HuBChE tetramers. Whereas HuBChE tetramers include short polyproline rich peptides derived from lamellipodin, no polyproline peptides have been identified in BoBChE. We hypothesize that BoBChE tetramers use a large polyproline-rich protein to organize subunits into a tetramer and that the low concentration of BoBChE in serum is explained by limited quantities of an unidentified polyproline-rich protein.

The effect of plasmapheresis on plasma cholinesterase levels in a patient with organophosphate poisoning

Objective: To describe the role of plasmapheresis in management of organophosphate poisonings. Design: Case report. Setting: A medical intensive care unit of a medical faculty. Patient: A patient with organophosphate poisoning whose cholinesterase levels continuously decline and then increase up to a normal level after plasmapheresis is performed for his sepsis. Interventions: Plasmapheresis with fresh frozen plasma. Measurements and main results: Baseline plasma cholinesterase (ChE) level was 4001 IU/L (normal values: 4000-10000 IU/L). Aspiration pneumonia was developed on day 3, and sepsis occurred on day 5. During this period, ChE levels gradually decreased. On day 5, plasmapheresis was performed for sepsis. Interestingly, plasma ChE levels increased from 2101 IU/L to 6144 IU/L after plasmapheresis. Atropine and pralidoxime were stopped, and a high level of ChE continued during hospitalization. The patient was successfully weaned from mechanical ventilation 3 days after plasmapheresis. Conclusion: Plasma exchange therapy may be considered for patients with organophosphate poisoning unresponsive to atropine and pralidoxime.

Tetramer-organizing polyproline-rich peptides differ in CHO cell-expressed and plasma-derived human butyrylcholinesterase tetramers

Tetrameric butyrylcholinesterase (BChE) in human plasma is the product of multiple genes, namely one BCHE gene on chromosome 3q26.1 and multiple genes that encode polyproline-rich peptides. The function of the polyproline-rich peptides is to assemble BChE into tetramers. CHO cells transfected with human BChE cDNA express BChE monomers and dimers, but only low quantities of tetramers. Our goal was to identify the polyproline-rich peptides in CHO-cell derived human BChE tetramers. CHO cell-produced human BChE tetramers were purified from serum-free culture medium. Peptides embedded in the tetramerization domain were released from BChE tetramers by boiling and identified by liquid chromatography-tandem mass spectrometry. A total of 270 proline-rich peptides were sequenced, ranging in size from 6-41 residues. The peptides originated from 60 different proteins that reside in multiple cell compartments including the nucleus, cytoplasm, and endoplasmic reticulum. No single protein was the source of the polyproline-rich peptides in CHO cell-expressed human BChE tetramers. In contrast, 70% of the tetramer-organizing peptides in plasma-derived BChE tetramers originate from lamellipodin. No protein source was identified for polyproline peptides containing up to 41 consecutive proline residues. In conclusion, the use of polyproline-rich peptides as a tetramerization motif is documented only for the cholinesterases, but is expected to serve other tetrameric proteins as well. The CHO cell data suggest that the BChE tetramer-organizing peptide can arise from a variety of proteins.

Comparison of 5 monoclonal antibodies for immunopurification of human butyrylcholinesterase on Dynabeads: KD values, binding pairs, and amino acid sequences

Human butyrylcholinesterase (HuBChE) is a stoichiometric bioscavenger of nerve agents and organophosphorus pesticides. Mass spectrometry methods detect stable nerve agent adducts on the active site serine of HuBChE. The first step in sample preparation is immunopurification of HuBChE from plasma. Our goal was to identify monoclonal antibodies that could be used to immunopurify HuBChE on Dynabeads Protein G. Mouse anti-HuBChE monoclonal antibodies were obtained in the form of ascites fluid, dead hybridoma cells stored frozen at -80 °C for 30 years, or recently frozen hybridoma cells. RNA from 4 hybridoma cell lines was amplified by PCR for determination of their nucleotide and amino acid sequences. Full-length light and heavy chains were expressed, and the antibodies purified from culture medium. A fifth monoclonal was purchased. The 5 monoclonal antibodies were compared for ability to capture HuBChE from human plasma on Dynabeads Protein G. In addition, they were evaluated for binding affinity by Biacore and ELISA. Epitope mapping by pairing analysis was performed on the Octet Red96 instrument. The 5 monoclonal antibodies, B2 12-1, B2 18-5, 3E8, mAb2, and 11D8, had similar KD values of 10(-9) M for HuBChE. Monoclonal B2 18-5 outperformed the others in the Dynabeads Protein G assay where it captured 97% of the HuBChE in 0.5 ml plasma. Pairing analysis showed that 3E8 and B2 12-1 share the same epitope, 11D8 and B2 18-5 share the same epitope, but mAb2 and B2 12-1 or mAb2 and 3E8 bind to different epitopes on HuBChE. B2 18-5 was selected for establishment of a stable CHO cell line for production of mouse anti-HuBChE monoclonal.

Review of human butyrylcholinesterase structure, function, genetic variants, history of use in the clinic, and potential therapeutic uses

Phase I clinical trials have shown that pure human butyrylcholinesterase (BChE) is safe when administered to humans. A potential therapeutic use of BChE is for prevention of nerve agent toxicity. A recombinant mutant of BChE that rapidly inactivates cocaine is being developed as a treatment to help recovering cocaine addicts avoid relapse into drug taking. These clinical applications rely on knowledge of the structure, stability, and properties of BChE, information that is reviewed here. Gene therapy with a vector that sustains expression for a year from a single injection is a promising method for delivering therapeutic quantities of BChE.

Polyproline promotes tetramerization of recombinant human butyrylcholinesterase

Human butyrylcholinesterase protects against nerve agents and pesticides, but the quantity of this plasma-derived tetrameric bioscavenger is limited. The present study demonstrates that recombinantly produced butyrylcholinesterase can be converted into stable tetramers without the cellular machinery by providing polyproline peptides.

His-tag truncated butyrylcholinesterase as a useful construct for in vitro characterization of wild-type and variant butyrylcholinesterases

Human butyrylcholinesterase (BChE) can scavenge and thereby provide protection against various toxic esters, including organophosphate-based chemical warfare agents and the recreational drug cocaine. It is currently being used in molecular evolution studies to generate novel enzymes with improved ability to hydrolyze toxic ester compounds. Currently, the most commonly used purification strategies for recombinant BChE enzymes involve using affinity resins based on small molecule interactions with the enzyme's substrate binding site. However, as BChE variants are discovered and developed, a generic purification protocol that is insensitive to amino acid substitutions is necessary. In the current manuscript, an expression vector encoding a C-terminal truncation and a His₆-tag was designed for BChE and used to express recombinant "wild-type" enzyme and two variants (i.e., G117H BChE and G117H/E197Q BChE). All the three His₆-tagged enzymes were successfully purified via metal-affinity columns using similar procedures with good recovery. Steady-state kinetic parameters were determined for each enzyme, and values were compared to those obtained with the corresponding non-truncated non-His₆-tagged enzymes. Rates of inhibition by echothiophate, a model compound for organophosphate-based pesticides, and rates of oxime-mediated reactivation after inhibition with a nerve agent model compound were also determined for selected enzymes. Rates of spontaneous reactivation from ETP inhibition were determined for the G117H variants. In all instances examined, truncation of the C-terminus of BChE and introduction of a His₆-tag had no significant effects on the observed kinetic parameters, making this a highly useful construct for in vitro characterization of wild-type and variant BChEs.

Exposure to tri-o-cresyl phosphate detected in jet airplane passengers

The aircraft cabin and flight deck ventilation are supplied from partially compressed unfiltered bleed air directly from the engine. Worn or defective engine seals can result in the release of engine oil into the cabin air supply. Aircrew and passengers have complained of illness following such "fume events". Adverse health effects are hypothesized to result from exposure to tricresyl phosphate mixed esters, a chemical added to jet engine oil and hydraulic fluid for its anti-wear properties. Our goal was to develop a laboratory test for exposure to tricresyl phosphate. The assay was based on the fact that the active-site serine of butyrylcholinesterase reacts with the active metabolite of tri-o-cresyl phosphate, cresyl saligenin phosphate, to make a stable phosphorylated adduct with an added mass of 80 Da. No other organophosphorus agent makes this adduct in vivo on butyrylcholinesterase. Blood samples from jet airplane passengers were obtained 24-48 h after completing a flight. Butyrylcholinesterase was partially purified from 25 ml serum or plasma, digested with pepsin, enriched for phosphorylated peptides by binding to titanium oxide, and analyzed by mass spectrometry. Of 12 jet airplane passengers tested, 6 were positive for exposure to tri-o-cresyl phosphate that is, they had detectable amounts of the phosphorylated peptide FGEpSAGAAS. The level of exposure was very low. No more than 0.05 to 3% of plasma butyrylcholinesterase was modified. None of the subjects had toxic symptoms. Four of the positive subjects were retested 3 to 7 months following their last airplane trip and were found to be negative for phosphorylated butyrylcholinesterase. In conclusion, this is the first report of an assay that detects exposure to tri-o-cresyl phosphate in jet airplane travelers.

Reaction of cresyl saligenin phosphate, the organophosphorus agent implicated in aerotoxic syndrome, with human cholinesterases: mechanistic studies employing kinetics, mass spectrometry, and X-ray structure analysis

Aerotoxic syndrome is assumed to be caused by exposure to tricresyl phosphate (TCP), an antiwear additive in jet engine lubricants and hydraulic fluid. CBDP (2-(ortho-cresyl)-4H-1,2,3-benzodioxaphosphoran-2-one) is the toxic metabolite of triortho-cresylphosphate, a component of TCP. Human butyrylcholinesterase (BChE; EC 3.1.1.8) and human acetylcholinesterase (AChE; EC 3.1.1.7) are irreversibly inhibited by CBDP. The bimolecular rate constants of inhibition (k(i)), determined under pseudo-first-order conditions, displayed a biphasic time course of inhibition with k(i) of 1.6 × 10(8) M(-1) min(-1) and 2.7 × 10(7) M(-1) min(-1) for E and E' forms of BChE. The inhibition constants for AChE were 1 to 2 orders of magnitude slower than those for BChE. CBDP-phosphorylated cholinesterases are nonreactivatable due to ultra fast aging. Mass spectrometry analysis showed an initial BChE adduct with an added mass of 170 Da from cresylphosphate, followed by dealkylation to a structure with an added mass of 80 Da. Mass spectrometry in (18)O-water showed that (18)O was incorporated only during the final aging step to form phospho-serine as the final aged BChE adduct. The crystal structure of CBDP-inhibited BChE confirmed that the phosphate adduct is the ultimate aging product. CBDP is the first organophosphorus agent that leads to a fully dealkylated phospho-serine BChE adduct.

Dichlorvos, chlorpyrifos oxon and Aldicarb adducts of butyrylcholinesterase, detected by mass spectrometry in human plasma following deliberate overdose

The goal of this study was to develop a method to detect pesticide adducts in tryptic digests of butyrylcholinesterase in human plasma from patients poisoned by pesticides. Adducts to butyrylcholinesterase in human serum may serve as biomarkers of pesticide exposure because organophosphorus and carbamate pesticides make a covalent bond with the active site serine of butyrylcholinesterase. Serum samples from five attempted suicides (with dichlorvos, Aldicarb, Baygon and an unknown pesticide) and from one patient who accidentally inhaled dichlorvos were analyzed. Butyrylcholinesterase was purified from 2 ml serum by ion exchange chromatography at pH 4, followed by procainamide affinity chromatography at pH 7. The purified butyrylcholinesterase was denatured, digested with trypsin and the modified peptide isolated by HPLC. The purified peptide was analyzed by multiple reaction monitoring in a QTRAP 4000 mass spectrometer. This method successfully identified the pesticide-adducted butyrylcholinesterase peptide in four patients whose butyrylcholinesterase was inhibited 60-84%, but not in two patients whose inhibition levels were 8 and 22%. It is expected that low inhibition levels will require analysis of larger serum plasma volumes. In conclusion, a mass spectrometry method for identification of exposure to live toxic pesticides has been developed, based on identification of pesticide adducts on the active site serine of human butyrylcholinesterase.

Transgenic plants as a source for the bioscavenging enzyme, human butyrylcholinesterase

Organophosphorous pesticides and nerve agents inhibit the enzyme acetylcholinesterase at neuronal synapses and in neuromuscular junctions. The resulting accumulation of acetylcholine overwhelms regulatory mechanisms, potentially leading to seizures and death from respiratory collapse. While current therapies are only capable of reducing mortality, elevation of the serum levels of the related enzyme butyrylcholinesterase (BChE) by application of the purified protein as a bioscavenger of organophosphorous compounds is effective in preventing all symptoms associated with poisoning by these toxins. However, BChE therapy requires large quantities of enzyme that can easily overwhelm current sources. Here, we report genetic optimization, cloning and high-level expression of human BChE in plants. Plant-derived BChE is shown to be biochemically similar to human plasma-derived BChE in terms of catalytic activity and inhibitor binding. We further demonstrate the ability of the plant-derived bioscavenger to protect animals against an organophosphorous pesticide challenge.

High-level expression of functional recombinant human butyrylcholinesterase in silkworm larvae by Bac-to-Bac system

Butyrylcholinesterase (BChE: EC 3.1.1.8) serves as a natural scavenger for a variety of drugs, poisons, and organophosphorous compounds by hydrolyzing their ester bonds. Large scale production of recombinant human BChE (rhBChE) has been reported in transgenic goat. Here we demonstrate high-level expression of rhBChE with biological activity comparable to that of natural and recombinant enzymes, through the Bac-to-Bac baculovirus expression system in silkworm Bombyx mori larvae. We constructed the full-length hBChE cDNA into the plasmid pFastBac. To monitor the level of expression, the cDNA coding for an orange fluorescent protein (OFP) was cloned downstream to the polyhedron (pH) promoter. Transfection was carried out by subcutaneous injection of 4-5th instar silkworm larvae. Approximately 4-7 days after infection, high-level expression of recombinant proteins was observed as indicated by the orange fluorescence of the larvae under blue light illumination. The hemolymph of the infected larvae was harvested, purified and assayed for BChE activity. The total units of BChE activity after purification were around 6.4 units per larvae. The K(m) and V(max) values of rhBChE were determined to be 17.7 microM and 2194 U/l hemolymph, respectively. By SDS-PAGE and Western analysis, the size of silkworm rhBChE was estimated to be 85 kDa. The results indicate that the silkworm larva is a good alternative system to produce bioactive rhBChE. Further optimization and modifications will be necessary for large-scale production of rhBChE. This should provide a rapid, low-cost, and high yield rhBChE for therapeutic applications.

Identification and characterization of biomarkers of organophosphorus exposures in humans

Over 1 billion pounds of organophosphorus (OP) chemicals are manufactured worldwide each year, including 70 million pounds of pesticides sprayed in the US. Current methods to monitor environmental and occupational exposures to OPs such as chlorpyrifos (CPS) have limitations, including low specificity and sensitivity, and short time windows for detection. Biomarkers for the OP tricresyl phosphate (TCP), which can contaminate bleed air from jet engines and cause an occupational exposure of commercial airline pilots, crewmembers and passengers, have not been identified. The aim of our work has been to identify, purify, and characterize new biomarkers of OP exposure. Butyrylcholinesterase (BChE) inhibition has been a standard for monitoring OP exposure. By identifying and characterizing molecular biomarkers with longer half-lives, we should be able to clinically detect TCP and OP insecticide exposure after longer durations of time than are currently possible. Acylpeptide hydrolase (APH) is a red blood cell (RBC) cytosolic serine proteinase that removes N-acetylated amino acids from peptides and cleaves oxidized proteins. Due to its properties, it is an excellent candidate for a biomarker of exposure. We have been able to purify APH and detect inhibition by both CPS and metabolites of TCP. The 120-day lifetime of the RBC offers a much longer window for detecting exposure. The OP-modified serine conjugate in the active site tryptic peptide has been characterized by mass spectrometry. This research uses functional proteomics and enzyme activities to identify and characterize useful biomarkers of neurotoxic environmental and occupational OP exposures.

Butyrylcholinesterase for protection from organophosphorus poisons: catalytic complexities and hysteretic behavior

Butyrylcholinesterase is a promiscuous enzyme that displays complex kinetic behavior. It is toxicologically important because it detoxifies organophosphorus poisons (OP) by making a covalent bond with the OP. The OP and the butyrylcholinesterase are both inactivated in the process. Inactivation of butyrylcholinesterase has no adverse effects. However, inactivation of acetylcholinesterase in nerve synapses can be lethal. OP-inhibited butyrylcholinesterase and acetylcholinesterase can be reactivated with oximes provided the OP has not aged. Strategies for preventing the toxicity of OP include (a) treatment with an OP scavenger, (b) reaction of non-aged enzyme with oximes, (c) reactivation of aged enzyme, (d) slowing down aging with peripheral site ligands, and (e) design of mutants that rapidly hydrolyze OP. Option (a) has progressed through phase I clinical trials with human butyrylcholinesterase. Option (b) is in routine clinical use. The others are at the basic research level. Butyrylcholinesterase displays complex kinetic behavior including activation by positively charged esters, ability to hydrolyze amides, and a lag time (hysteresis) preceding hydrolysis of benzoylcholine and N-methylindoxyl acetate. Mass spectrometry has identified new OP binding motifs on tyrosine and lysine in proteins that have no active site serine. It is proposed, but not yet proven, that low dose exposure involves OP modification of proteins that have no active site serine.

Carbofuran poisoning detected by mass spectrometry of butyrylcholinesterase adduct in human serum

Carbofuran is a pesticide whose acute toxicity is due to inhibition of acetylcholinesterase. Butyrylcholinesterase (BChE) in plasma is inhibited by carbofuran and serves as a biomarker of poisoning by carbofuran. The goal was to develop a method to positively identify poisoning by carbofuran. Sera from an attempted murder and an attempted suicide were analyzed for the presence of carbofuran adducts on BChE. The BChE from 1 ml of serum was rapidly purified on a 0.2 ml procainamide-Sepharose column. Speed was essential because the carbofuran-BChE adduct decarbamylates with a half-life of about 2 h. The partially purified BChE was boiled to denature the protein, thus stopping decarbamylation and making the protein vulnerable to digestion with trypsin. The labeled peptide was partially purified by HPLC before analysis by LC/MS/MS in the multiple reaction monitoring mode on the QTRAP 2000 mass spectrometer. Carbofuran was found to be covalently bound to Ser 198 of human BChE in serum samples from two poisoning cases. Multiple reaction monitoring triggered MS/MS spectra positively identified the carbofuran-BChE adduct. In conclusion a mass spectrometry method to identify carbofuran poisoning in humans has been developed. The method uses 1 ml of serum and detects low-level exposure associated with as little as 20% inhibition of plasma butyrylcholinesterase.

Direct correlation between molecular dynamics and enzymatic stability: a comparative neutron scattering study of native human butyrylcholinesterase and its "aged" soman conjugate

An incoherent elastic neutron scattering study of the molecular dynamics of native human butyrylcholinesterase and its "aged" soman-inhibited conjugate revealed a significant change in molecular flexibility on an angstrom-nanosecond scale as a function of temperature. The results were related to the stability of each state as established previously by differential scanning calorimetry. A striking relationship was found between the denaturation behavior and the molecular flexibility of the native and inhibited enzymes as a function of temperature. This was reflected in a quantitative correlation between the atomic mean-square displacements on an angstrom-nanosecond scale determined by neutron spectroscopy and the calorimetric specific heat. By the application of a simple two-state model that describes the transition from a folded to a denatured state, the denaturation temperatures of the native and the inhibited enzyme were correctly extracted from the atomic mean-square displacements. Furthermore, the transition entropy and enthalpy extracted from the model fit of the neutron data were, within the experimental accuracy, compatible with the values determined by differential scanning calorimetry.

Hairy-root organ cultures for the production of human acetylcholinesterase

BACKGROUND

Human cholinesterases can be used as a bioscavenger of organophosphate toxins used as pesticides and chemical warfare nerve agents. The practicality of this approach depends on the availability of the human enzymes, but because of inherent supply and regulatory constraints, a suitable production system is yet to be identified.

RESULTS

As a promising alternative, we report the creation of "hairy root" organ cultures derived via Agrobacterium rhizogenes-mediated transformation from human acetylcholinesterase-expressing transgenic Nicotiana benthamiana plants. Acetylcholinesterase-expressing hairy root cultures had a slower growth rate, reached to the stationary phase faster and grew to lower maximal densities as compared to wild type control cultures. Acetylcholinesterase accumulated to levels of up to 3.3% of total soluble protein, ~3 fold higher than the expression level observed in the parental plant. The enzyme was purified to electrophoretic homogeneity. Enzymatic properties were nearly identical to those of the transgenic plant-derived enzyme as well as to those of mammalian cell culture derived enzyme. Pharmacokinetic properties of the hairy-root culture derived enzyme demonstrated a biphasic clearing profile. We demonstrate that master banking of plant material is possible by storage at 4 degrees C for up to 5 months.

CONCLUSION

Our results support the feasibility of using plant organ cultures as a successful alternative to traditional transgenic plant and mammalian cell culture technologies.

Developing procedures for the large-scale purification of human serum butyrylcholinesterase

Human serum butyrylcholinesterase (Hu BChE) is the most viable candidate for the prophylactic treatment of organophosphate poisoning. A dose of 200 mg/70 kg is predicted to protect humans against 2x LD(50) of soman. Therefore, the aim of this study was to develop procedures for the purification of gram quantities of this enzyme from outdated human plasma or Cohn Fraction IV-4. The purification of Hu BChE was accomplished by batch adsorption on procainamide-Sepharose-CL-4B affinity gel followed by ion-exchange chromatography on a DEAE-Sepharose column. For the purification of enzyme from Cohn Fraction IV-4, it was resuspended in 25 mM sodium phosphate buffer, pH 8.0, and fat was removed by decantation, prior to batch adsorption on procainamide-Sepharose gel. In both cases, the procainamide gel was thoroughly washed with 25 mM sodium phosphate buffer, pH 8.0, containing 0.05 M NaCl, and the enzyme was eluted with the same buffer containing 0.1 M procainamide. The enzyme was dialyzed and the pH was adjusted to 4.0 before loading on the DEAE column equilibrated in sodium acetate buffer, pH 4.0. The column was thoroughly washed with 25 mM sodium phosphate buffer, pH 8.0 containing 0.05 M NaCl before elution with a gradient of 0.05-0.2M NaCl in the same buffer. The purity of the enzyme following these steps ranged from 20% to 40%. The purity of the enzyme increased to >90% by chromatography on an analytical procainamide affinity column. Results show that Cohn Fraction IV-4 is a much better source than plasma for the large-scale isolation of purified Hu BChE.

Fast affinity purification coupled with mass spectrometry for identifying organophosphate labeled plasma butyrylcholinesterase

Classical plasma butyrylcholinesterase (BChE) purification involves dialysis and multiple steps of chromatography. We describe a procainamide affinity gel purification scheme that takes 15-30 min to purify BChE from 1 ml plasma. The method uses a microfuge spin column to build a 0.2 ml procainamide affinity column. The eluted BChE contains 3-4 microg of 500-fold purified BChE, free from 99% of contaminating plasma proteins. The BChE was further purified by gel electrophoresis. Tryptic peptides from the BChE containing gel electrophoresis band were prepared by in-gel digestion, separated by reverse phase liquid chromatography and identified by mass spectrometry. The 29 residue active site tryptic peptide labeled with the nerve agents soman or sarin was identified.

Plant-derived human acetylcholinesterase-R provides protection from lethal organophosphate poisoning and its chronic aftermath

Therapeutically valuable proteins are often rare and/or unstable in their natural context, calling for production solutions in heterologous systems. A relevant example is that of the stress-induced, normally rare, and naturally unstable "read-through" human acetylcholinesterase variant, AChE-R. AChE-R shares its active site with the synaptic AChE-S variant, which is the target of poisonous organophosphate anticholinesterase insecticides such as the parathion metabolite paraoxon. Inherent AChE-R overproduction under organophosphate intoxication confers both short-term protection (as a bioscavenger) and long-term neuromuscular damages (as a regulator). Here we report the purification, characterization, and testing of human, endoplasmic reticulum-retained AChE-R(ER) produced from plant-optimized cDNA in Nicotiana benthamiana plants. AChE-R(ER) purified to homogeneity showed indistinguishable biochemical properties, with IC50 = 10(-7) M for the organophosphate paraoxon, similar to mammalian cell culture-derived AChE. In vivo titration showed dose-dependent protection by intravenously injected AChE-R(ER) of FVB/N male mice challenged with a lethal dose of paraoxon, with complete elimination of short-term clinical symptoms at near molar equivalence. By 10 days postexposure, AChE-R prophylaxis markedly limited postexposure increases in plasma murine AChE-R levels while minimizing the organophosphate-induced neuromuscular junction dismorphology. Our findings present plant-produced AChE-R(ER) as a bimodal agent, conferring both short- and long-term protection from organophosphate intoxication.

Butyrylcholinesterase activity and molecular components in thymus of healthy and merosin-deficient Lama2dy mice

The laminin-alpha2 chain, referred to as merosin, forms part of the laminin-2 heterotrimer (alpha2beta1gamma1), which is principally expressed in the basement membrane of muscle. Nearly half of patients suffering from congenital muscular dystrophy (CMD) have abnormalities in the laminin-alpha2 chain (LAMA2) gene, and the merosin-deficient Lama2dy mouse shows CMD. The expression of merosin in thymus, the abnormalities in the gland of Lama2dy mice, and the presence of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in thymus prompted us to study the possible effects of the deficiency of merosin on thymus BuChE. We found that, while AChE activity decreased by approximately 50% in merosin-deficient thymus, the deficiency had little effect on BuChE activity. About 65% of thymus BuChE activity was extracted with a saline buffer and 30% with 1% Triton X-100. Sedimentation analyses and phenyl-agarose chromatography showed that thymus contained amphiphilic BuChE monomers (G(1)(A),44%) and dimers (G(2)(A),33%), and hydrophilic tetramers (G(4)(H),23%). Binding assays with various plant lectins revealed differences between the oligoglycans linked to BuChE tetramers and lighter components. The deficiency of merosin had no effect on the biosynthesis of thymus BuChE as judged by the lack of major changes between control and Lama2dy mice thymuses in the distribution of BuChE molecules and the level of lectin binding. The detoxifying action of BuChE, its role as a backup to AChE, and the relevance of the cholinergic dialogue between T cells and stromal cells for T lymphocyte proliferation, maturation and survival support a physiological function for BuChE in thymus.

Verification of Exposure to Organophosphates: Generic Mass Spectrometric Method for Detection of Human Butyrylcholinesterase Adducts

We present a generic mass spectrometric method to verify exposure to organophosphates, based on the chemical conversion of the phosphylated peptides obtained after pepsin digestion of human butyrylcholinesterase (HuBuChE) to a common precursor peptide. After exposure of plasma to various organophosphates (nerve agents, pesticides), HuBuChE was isolated from plasma by procainamide affinity-based solid-phase extraction. Upon subsequent pepsin digestion, the respective phosphylated nonapeptides could be identified in the digests. After treatment of the pepsin digests with Ba(OH)2 in the presence of a nucleophilic tag (a thiol or amine), the phosphylated nonapeptides were transformed into a common tagged nonapeptide that could be analyzed sensitively by means of LC tandem MS. So far, best results were obtained with 2-(3-aminopropylamino)ethanol as nucleophilic tag. By applying the presented method, HuBuChE inhibition can now be monitored accurately by mass spectrometry, without advance knowledge of the structure of the inhibitor.

Naturally occurring mutation Leu307Pro of human butyrylcholinesterase in the Vysya community of India

BACKGROUND

People with genetic variants of butyrylcholinesterase (EC 3.1.1.8, BChE) can have hours of prolonged apnea after a normal dose of succinylcholine or mivacurium.

METHODS

Plasma samples from 226 people in the Vysya community in Coimbatore, India were tested for BChE activity.

RESULTS

Nine unrelated individuals had no detectable activity. DNA sequencing revealed a novel mutation in exon 2 of the BCHE gene, responsible for the silent phenotype of human serum BChE. All silent BChE samples were homozygous for a point mutation at codon 307 (CTT-->CCT), resulting in substitution of leucine 307 by proline. Western blot analysis with a monoclonal antibody showed no BChE protein in plasma. Silent BChE plasma samples had no organophosphate-reactive BChE, as measured with FP-biotin. Expression of recombinant Leu307Pro BChE in cell culture confirmed that this mutant is expressed at very low levels. The proline substitution most likely destabilizes the BChE structure and causes the protein to be misfolded and rapidly degraded.

CONCLUSIONS

This is the first report of a molecularly defined BChE mutation in the Indian population. The frequency of homozygous silent BChE in the Vysya community is 1 in 24, a value 4000-fold higher than the frequency of homozygous silent BChE in European and American populations.

Purification of transgenic plant-derived recombinant human acetylcholinesterase-R

Nicotiana benthamiana plants were engineered to express a codon-optimized gene encoding the human acetylcholinesterase-R (AChE) isoform. The transgenic plants expressed the protein at >0.4% of total soluble protein, and the plant-produced enzyme was purified to homogeneity. Following lysis, procainamide affinity chromatography and anion-exchange chromatography, more than 400-fold purification was achieved and electrophoretic purity was obtained. This pure protein is kinetically indistinguishable from the only commercially available source of human acetylcholinesterase, which is produced in mammalian cell culture. Thus, we have demonstrated a model system for the production of acetylcholinesterase, which is not susceptible to the quantitative limitations or mammalian pathogens associated with purification from mammalian cell culture or human serum.

Effects of soman inhibition and of structural differences on cholinesterase molecular dynamics: a neutron scattering study

Incoherent elastic neutron scattering experiments on members of the cholinesterase family were carried out to investigate how molecular dynamics is affected by covalent inhibitor binding and by differences in primary and quaternary structure. Tetrameric native and soman-inhibited human butyrylcholinesterase (HuBChE) as well as native dimeric Drosophila melanogaster acetylcholinesterase (DmAChE) hydrated protein powders were examined. Atomic mean-square displacements (MSDs) were found to be identical for native HuBChE and for DmAChE in the whole temperature range examined, leading to the conclusion that differences in activity and substrate specificity are not reflected by a global modification of subnanosecond molecular dynamics. MSDs of native and soman-inhibited HuBChE were identical below the thermal denaturation temperature of the native enzyme, indicating a common mean free-energy surface. Denaturation of the native enzyme is reflected by a relative increase of MSDs consistent with entropic stabilization of the unfolded state. The results suggest that the stabilization of HuBChE phosphorylated by soman is due to an increase in free energy of the unfolded state due to a decrease in entropy.

The influence of solvent composition on global dynamics of human butyrylcholinesterase powders: a neutron-scattering study

A major result of incoherent elastic neutron-scattering experiments on protein powders is the strong dependence of the intramolecular dynamics on the sample environment. We performed a series of incoherent elastic neutron-scattering experiments on lyophilized human butyrylcholinesterase (HuBChE) powders under different conditions (solvent composition and hydration degree) in the temperature range from 20 to 285 K to elucidate the effect of the environment on the enzyme atomic mean-square displacements. Comparing D(2)O- with H(2)O-hydrated samples, we were able to investigate protein as well as hydration water molecular dynamics. HuBChE lyophilized from three distinct buffers showed completely different atomic mean-square displacements at temperatures above approximately 200 K: a salt-free sample and a sample containing Tris-HCl showed identical small-amplitude motions. A third sample, containing sodium phosphate, displayed highly reduced mean-square displacements at ambient temperature with respect to the other two samples. Below 200 K, all samples displayed similar mean-square displacements. We draw the conclusion that the reduction of intramolecular protein mean-square displacements on an Angstrom-nanosecond scale by the solvent depends not only on the presence of salt ions but also on their type.

The effects of fresh frozen plasma on cholinesterase levels and outcomes in patients with organophosphate poisoning

OBJECTIVE

The aim of this study is to determine the effects of fresh frozen plasma, as a source of cholinesterase, on butyrylcholinesterase (BuChE; plasma or pseudo cholinesterase) levels and outcomes in patients with organophosphate poisoning.

MATERIALS AND METHODS

This prospective study was performed at the Department of Intensive Care of Erciyes University Medical School. Over 2 yrs, patients admitted to the ICU for OP poisoning were entered into the study. OP poisoning was diagnosed on the basis of history and BuChE levels. All patients received atropine. Fresh frozen plasma was given to 12 patients. The study was approved by the Ethical Committee, and verbal informed consent was obtained.

RESULTS

Thirty-three patients were included in the study. BuChE levels measured at admission and the pralidoxime and atropine doses administered were not different between groups (p>0.05). Although intermediate syndrome developed in 28.6% of patients receiving pralidoxime, there were no intermediate syndrome cases in patients receiving plasma prior to developing intermediate syndrome. The mortality rates were 14.3% in the pralidoxime group and 0% in the plasma+atropine+pralidoxime group. Two patients received plasma after developing the intermediate syndrome, and one patient who received only atropine died. BuChE levels of fresh frozen plasma were 4069.5 +/- 565.1 IU/L. Every two bags of plasma provided an increase in BuChE levels of approximately 461.7 +/- 142.1 IU/L.

CONCLUSION

Fresh frozen plasma therapy increases BuChE levels in patients with organophosphate poisonings. The administration of plasma may also prevent the development of intermediate syndrome and related mortality. Plasma (fresh frozen or freshly prepared) therapy may be used as an alternative or adjunctive treatment method in patients with organophosphate pesticide poisoning, especially in cases not given pralidoxime. Further randomized controlled and animal studies are required to infer a definitive result.

Cholinesterase inhibitors modify the activity of intrinsic cardiac neurons

Cholinesterase inhibitors used to treat the symptoms of Alzheimer's disease (AD) inhibit both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), albeit to different degrees. Because central and peripheral neurons, including intrinsic cardiac neurons located on the surface of the mammalian heart, express both BuChE and AChE, we studied spontaneously active intrinsic cardiac neurons in the pig as a model to assess the effects of inhibition of AChE compared to BuChE. Neuroanatomical experiments showed that some porcine intrinsic cardiac neurons expressed AChE and/or BuChE. Enzyme kinetic experiments with cholinesterase inhibitors, namely, donepezil, galantamine, (+/-) huperzine A, metrifonate, rivastigmine, and tetrahydroaminoacridine, demonstrated that these compounds differentially inhibited porcine AChE and BuChE. Donepezil and (+/-) huperzine A were better reversible inhibitors of AChE, and galantamine equally inhibited both the enzymes. Tetrahydroaminoacridine was a better reversible inhibitor of BuChE. Rivastigmine caused more rapid inactivation of BuChE as compared to AChE. Neurophysiological studies showed that acetylcholine and butyrylcholine increase or decrease the spontaneous activity of the intrinsic cardiac neurons. Donepezil, galantamine, (+/-) huperzine A, and tetrahydroaminoacridine changed spontaneous neuronal activity by about 30-35 impulses per minute, while rivastigmine changed it by approximately 100 impulses per minute. It is concluded that (i) inhibition of AChE and BuChE directly affects the porcine intrinsic cardiac nervous system, (ii) the intrinsic cardiac nervous system represents a suitable model for examining the effects of cholinesterase inhibitors on mammalian neurons in vivo, and (iii) the activity of intrinsic cardiac neurons may be affected by pharmacological agents that inhibit cholinesterases.

Laboratory setup for long-term monitoring of the volatilization of hazardous materials: preliminary tests of O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothiolate on asphalt

Contrary to commonly used pesticides, the rate of volatilization of extremely toxic chemicals such as the nerve agent O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothiolate (VX) cannot be readily obtained under environmental conditions due to its high mammalian toxicity that would require extraordinary precautions. An alternative is a laboratory setup that would be used to obtain environmentally relevant data required for risk assessment studies. In this paper we describe a newly designed climatic hood that enables control of temperature, humidity, and air velocity within less than +/- 0.5% fluctuations during continuous operation. The performance of the evaporation system togetherwith the sampling and analytical procedures produced a meaningful concentration profile of vapors obtained from a 15 mg sample of VX dispersed as small droplets over a 10 x 16 cm piece of asphalt road. The released vapors amounted to approximately 30% of the applied mass, and its time course was best fitted to a triexponential curve with rate constants changing over time from 2.2 to 0.03 h(-1). The asphalt enhanced a specific degradation pathway of VX that is relatively minor in aqueous solutions. Results provide the first data on the volatilization of VX from samples of asphalt road, and offer an insight into VX behavior in the environment.

The effect of fluoride on the scavenging of organophosphates by human butyrylcholinesterase in buffer solutions and human plasma

Fluoride ion is a reversible inhibitor of human butyrylcholinesterase (HuBChE) that is a viable drug candidate against organophosphates (OPs) toxicity. Since large numbers of communities in many countries are occasionally exposed to relatively high amount of fluoride, its effect on the kinetics of inhibition of HuBChE by OPs was investigated. In saline phosphate, pH 7.4, fluoride in the lower millimolar range significantly slowed the inhibition of HuBChE by paraoxon, DFP, echothiophate, soman, sarin, and VX. The kinetics of the inhibition was found consistent with the formation of a reversible fluoride-HuBChE complex that is at least 25-fold less active towards phosphorylation or phosphonylation than the free enzyme. Heat inactivation experiments indicate that the binding of fluoride to HuBChE probably involves enhanced cross-domain interaction via hydrogen bonds formation that may decrease enzyme activity. In spite of distinct structural differences among the OP used, the dissociation constants of the fluoride-HuBChE reversible complex varied over a narrow range (KF, 0.31-0.70 mM); however, KF in human plasma increased to 2.75-3.40 mM. 19F-NMR spectroscopy revealed that fluoride ion is complexed to plasma components, an observation that explains in part the apparent increase in KF. Results suggest that an estimate of the relative decrease in the rate of OPs sequestration in presence of fluoride can be obtained from the fraction of the free HuBChE (1 + [F]/K(F))(-1). Considering KF values in human plasma, it is concluded that the scavenging efficacy of OPs by HuBChE is not compromised by the normal concentration range of circulating fluoride ions.

Estimation of the upper limit of human butyrylcholinesterase dose required for protection against organophosphates toxicity: a mathematically based toxicokinetic model

Human butyrylcholinesterase (HuBChE) is a drug candidate for protection against organophosphates (OP) intoxication. A mathematically based model was validated and employed to better understand the role of the endogenous HuBChE in detoxification of OPs and to estimate the dose of exogenous HuBChE required for enhancing protection of humans from lethal exposure to OPs. The model addresses the relationship between the HuBChE dose needed to maintain a certain residual activity of human acetylcholinesterase (HuAChE) and the following parameters: (1) level and duration of exposure, (2) bimolecular rate constants of inhibition of HuAChE (kA) and HuBChE (kB) by OPs, and (3) time elapsed from enzyme load. The equation derived for the calculation of HuBChE dose requires the knowledge of kA/kB in human blood and the rate constant of HuBChE elimination. Predictions of HuBChE doses were validated by in vitro experiments and data of published human studies. These predictions highlight two parameters that are likely to decrease the calculated dose: (1) the rapid consumption of the less toxic isomers of OPs in human plasma, and (2) the volume of distribution of HuBChE that appears significantly greater than the volume of plasma. The first part of the analysis of the proposed model was focused on acute bolus exposures and suggests that upper limit doses of 134, 115, and 249 mg/70 kg are sufficient to protect RBC AChE above 30% of baseline activity following a challenge with 1 LD(50) VX, soman, and sarin, respectively. The principles of the validated model should be applicable for advanced predictions of HuBChE dose for protection against continuous exposures to OPs.