Hupresin Retains Binding Capacity for Butyrylcholinesterase and Acetylcholinesterase after Sanitation with Sodium Hydroxide

Human butyrylcholinesterase in Cohn fraction IV-4 purified in a single chromatography step on Hupresin

Protection from the toxicity of nerve agents is achieved by pretreatment with human butyrylcholinesterase (BChE). Current methods for purifying large quantities of BChE from frozen Cohn fraction IV-4 produce 99% pure enzyme, but the yield is low (21%). Our goal was to simplify the purification procedure and increase the yield. Butyrylcholinesterase was extracted from frozen Cohn fraction IV-4 in 10 volumes of water pH 6. The filtered extract was pumped onto a Hupresin affinity column. The previously utilized anion exchange chromatography step was omitted. Solvent and detergent reagents used to inactivate lipid enveloped virus, bacteria and protozoa did not bind to Hupresin. BChE was eluted with 0.1 M tetramethylammonium bromide in 20 mM sodium phosphate pH 8.0. BChE protein was concentrated on a Pellicon tangential flow filtration system and demonstrated to be highly purified by mass spectrometry. A high pump rate produced protein aggregates, but a low pump rate caused minimal turbidity. Possible contamination by prekallikrein and prekallikrein activator was examined by LC-MS/MS and by a chromogenic substrate assay for kallikrein activity. Prekallikrein and kallikrein were not detected by mass spectrometry in the 99% pure BChE. The chromogenic assay indicated kallikrein activity was less than 9 mU/mL. This new, 1-step chromatography protocol on Hupresin increased the yield of butyrylcholinesterase by 200%. The new method significantly reduces production costs by optimizing yield of 99% pure butyrylcholinesterase.

Butyrylcholinesterase-Protein Interactions in Human Serum

Measuring various biochemical and cellular components in the blood is a routine procedure in clinical practice. Human serum contains hundreds of diverse proteins secreted from all cells and tissues in healthy and diseased states. Moreover, some serum proteins have specific strong interactions with other blood components, but most interactions are probably weak and transient. One of the serum proteins is butyrylcholinesterase (BChE), an enzyme existing mainly as a glycosylated soluble tetramer that plays an important role in the metabolism of many drugs. Our results suggest that BChE interacts with plasma proteins and forms much larger complexes than predicted from the molecular weight of the BChE tetramer. To investigate and isolate such complexes, we developed a two-step strategy to find specific protein–protein interactions by combining native size-exclusion chromatography (SEC) with affinity chromatography with the resin that specifically binds BChE. Second, to confirm protein complexes′ specificity, we fractionated blood serum proteins by density gradient ultracentrifugation followed by co-immunoprecipitation with anti-BChE monoclonal antibodies. The proteins coisolated in complexes with BChE were identified by mass spectroscopy. These binding studies revealed that BChE interacts with a number of proteins in the human serum. Some of these interactions seem to be more stable than transient. BChE copurification with ApoA-I and the density of some fractions containing BChE corresponding to high-density lipoprotein cholesterol (HDL) during ultracentrifugation suggest its interactions with HDL. Moreover, we observed lower BChE plasma activity in individuals with severely reduced HDL levels (≤20 mg/dL). The presented two-step methodology for determination of the BChE interactions can facilitate further analysis of such complexes, especially from the brain tissue, where BChE could be involved in the pathogenesis and progression of AD.

Pyridinium-2-carbaldoximes with quinolinium carboxamide moiety are simultaneous reactivators of acetylcholinesterase and butyrylcholinesterase inhibited by nerve agent surrogates

The pyridinium-2-carbaldoximes with quinolinium carboxamide moiety were designed and synthesised as cholinesterase reactivators. The prepared compounds showed intermediate-to-high inhibition of both cholinesterases when compared to standard oximes. Their reactivation ability was evaluated in vitro on human recombinant acetylcholinesterase (hrAChE) and human recombinant butyrylcholinesterase (hrBChE) inhibited by nerve agent surrogates (NIMP, NEMP, and NEDPA) or paraoxon. In the reactivation screening, one compound was able to reactivate hrAChE inhibited by all used organophosphates and two novel compounds were able to reactivate NIMP/NEMP-hrBChE. The reactivation kinetics revealed compound 11 that proved to be excellent reactivator of paraoxon-hrAChE better to obidoxime and showed increased reactivation of NIMP/NEMP-hrBChE, although worse to obidoxime. The molecular interactions of studied reactivators were further identified by in silico calculations. Molecular modelling results revealed the importance of creation of the pre-reactivation complex that could lead to better reactivation of both cholinesterases together with reducing particular interactions for lower intrinsic inhibition by the oxime.

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.

Effects of Kifunensine on Production and N-Glycosylation Modification of Butyrylcholinesterase in a Transgenic Rice Cell Culture Bioreactor

The production and N-glycosylation of recombinant human butyrylcholinesterase (BChE), a model highly glycosylated therapeutic protein, in a transgenic rice cell suspension culture treated with kifunensine, a strong α-mannosidase I inhibitor, was studied in a 5 L bioreactor. A media exchange was performed at day 7 of cultivation by removing spent sugar-rich medium (NB+S) and adding fresh sugar-free (NB-S) medium to induce the rice α-amylase 3D (RAmy3D) promoter to produce rice recombinant human BChE (rrBChE). Using a 1.25X-concentrated sugar-free medium together with an 80% reduced working volume during the media exchange led to a total active rrBChE production level of 79 ± 2 µg (g FW)^-1 or 7.5 ± 0.4 mg L^-1 in the presence of kifunensine, which was 1.5-times higher than our previous bioreactor runs using normal sugar-free (NB-S) media with no kifunensine treatment. Importantly, the amount of secreted active rrBChE in culture medium was enhanced in the presence of kifunensine, comprising 44% of the total active rrBChE at day 5 following induction. Coomassie-stained SDS-PAGE gel and Western blot analyses revealed different electrophoretic migration of purified rrBChE bands with and without kifunensine treatment, which was attributed to different N-glycoforms. N-Glycosylation analysis showed substantially increased oligomannose glycans (Man5/6/7/8) in rrBChE treated with kifunensine compared to controls. However, the mass-transfer limitation of kifunensine was likely the major reason for incomplete inhibition of α-mannosidase I in this bioreactor study.

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.

Kinetically-controlled mechanism-based isolation of metabolic serine hydrolases in active form from complex proteomes: butyrylcholinesterase as a case study

In this work an activity-based probe containing a carbamate group was designed to isolate human butyrylcholinesterase (hBChE), a metabolic serine hydrolase (mSH), from complex proteomes. The method took advantage of the native interaction mechanism of mSHs with carbamate pseudo-substrates for temporarily capturing the enzyme on a resin functionalized with the carbamate probe and releasing the enzyme in active form after removal of the contaminating proteins. The isolation relied on the possibility of manipulating the carbamylation and decarbamylation kinetics favoring the former during the capture and wash steps and the latter in the release step. The designed probe captured and released all the active hBChE isoenzymes present in plasma with high selectivity (up to ∼2000-fold purification) and reasonable yields (17% to 36%). The parameters affecting the performance were the incubation time used in the load and elution steps, the plasma to resin volumetric ratio, the elution temperature and the nature and concentration of the eluting agent. The carbamate resin could be prepared either by coupling a fully synthesized probe with an activated resin or by building the probe onto the resin by a step-by-step procedure, without major differences in performance between the two routes. The prepared resins allowed to process up to about 8.5 mL of plasma per g of resin with constant performance. Since the method was based on the general catalytic cycle of mSHs, we expect this approach to be applicable to other enzymes of the family, by selecting a suitable target-selective feature to link to the carbamate group.

The modulation of the equilibrium between carbamylation and decarbamylation kinetics is used to isolate a model metabolic serine hydrolase.

Structural stability of human butyrylcholinesterase under high hydrostatic pressure

Human butyrylcholinesterase is a nonspecific enzyme of clinical, pharmacological and toxicological significance. Although the enzyme is relatively stable, its activity is affected by numerous factors, including pressure. In this work, hydrostatic pressure dependence of the intrinsic tryptophan fluorescence in native and salted human butyrylcholinesterase was studied up to the maximum pressure at ambient temperature of about 1200 MPa. A correlated large shift toward long wavelengths and broadening observed at pressures between 200 and 700 MPa was interpreted as due to high pressure-induced denaturation of the protein, leading to an enhanced exposure of tryptophan residues into polar solvent environment. This transient process in native butyrylcholinesterase presumably involves conformational changes of the enzyme at both tertiary and secondary structure levels. Pressure-induced mixing of emitting local indole electronic transitions with quenching charge transfer states likely describes the accompanying fluorescence quenching that reveals different course from spectral changes. All the pressure-induced changes turned irreversible after passing a mid-point pressure of about 400 ± 50 MPa. Addition of either 0.1 M ammonium sulphate (a kosmotropic salt) or 0.1 M lithium thiocyanate (a chaotropic salt) to native enzyme similarly destabilized its structure.

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.

Optimization of Cholinesterase-Based Catalytic Bioscavengers Against Organophosphorus Agents

Organophosphorus agents (OPs) are irreversible inhibitors of acetylcholinesterase (AChE). OP poisoning causes major cholinergic syndrome. Current medical counter-measures mitigate the acute effects but have limited action against OP-induced brain damage. Bioscavengers are appealing alternative therapeutic approach because they neutralize OPs in bloodstream before they reach physiological targets. First generation bioscavengers are stoichiometric bioscavengers. However, stoichiometric neutralization requires administration of huge doses of enzyme. Second generation bioscavengers are catalytic bioscavengers capable of detoxifying OPs with a turnover. High bimolecular rate constants (k_cat/K_m > 10⁶ M⁻¹min⁻¹) are required, so that low enzyme doses can be administered. Cholinesterases (ChE) are attractive candidates because OPs are hemi-substrates. Moderate OP hydrolase (OPase) activity has been observed for certain natural ChEs and for G117H-based human BChE mutants made by site-directed mutagenesis. However, before mutated ChEs can become operational catalytic bioscavengers their dephosphylation rate constant must be increased by several orders of magnitude. New strategies for converting ChEs into fast OPase are based either on combinational approaches or on computer redesign of enzyme. The keystone for rational conversion of ChEs into OPases is to understand the reaction mechanisms with OPs. In the present work we propose that efficient OP hydrolysis can be achieved by re-designing the configuration of enzyme active center residues and by creating specific routes for attack of water molecules and proton transfer. Four directions for nucleophilic attack of water on phosphorus atom were defined. Changes must lead to a novel enzyme, wherein OP hydrolysis wins over competing aging reactions. Kinetic, crystallographic, and computational data have been accumulated that describe mechanisms of reactions involving ChEs. From these studies, it appears that introducing new groups that create a stable H-bonded network susceptible to activate and orient water molecule, stabilize transition states (TS), and intermediates may determine whether dephosphylation is favored over aging. Mutations on key residues (L286, F329, F398) were considered. QM/MM calculations suggest that mutation L286H combined to other mutations favors water attack from apical position. However, the aging reaction is competing. Axial direction of water attack is not favorable to aging. QM/MM calculation shows that F329H+F398H-based multiple mutants display favorable energy barrier for fast reactivation without aging.

Use of Hupresin To Capture Red Blood Cell Acetylcholinesterase for Detection of Soman Exposure

Toxicity from acute exposure to nerve agents and organophosphorus toxicants is due to irreversible inhibition of acetylcholinesterase (AChE) in the nervous system. AChE in red blood cells is a surrogate for AChE in the nervous system. Previously we developed an immunopurification method to enrich red blood cell AChE (RBC AChE) as a biomarker of exposure. The goal of the present work was to provide an alternative RBC AChE enrichment strategy, by binding RBC AChE to Hupresin affinity gel. AChE was solubilized from frozen RBC by addition of 1% Triton X-100. Insoluble debris was removed by centrifugation. The red, but not viscous, RBC AChE solution was loaded on a Hupresin affinity column. Hemoglobin and other proteins were washed off with 3 M NaCl, while retaining AChE bound to Hupresin. Denatured AChE was eluted with 1% trifluoroacetic acid. The same protocol was used for 20 mL of RBC AChE inhibited with a soman model compound. The acid denatured protein was digested with pepsin and analyzed by liquid chromatography tandem mass spectrometry on a 6600 Triple-TOF mass spectrometer. A targeted method identified the aged soman adduct on serine 203 in peptide FGESAGAAS. It was concluded that Hupresin can be used to enrich soman-inhibited AChE solubilized from 8 mL of frozen human erythrocytes, yielding a quantity sufficient for detecting soman exposure.