Human serum butyrylcholinesterase interactions with cisplatin and cyclophosphamide

Human serum Butyrylcholinesterase (BChE) is an important enzyme in detoxification with its capacity for hydrolyzing esters. The inhibitory effect of cisplatin (CDDP) and cyclophosphamide (CY) on BChE is characterized. Time dependent inhibition of BChE with both chemotherapeutics was rapid, reversible. CY was found as non-competitive inhibitor with Ki of 503.6 ± 50.4 μM. Time dependent CDDP studies displayed progressive inhibition. The constants for apparent dissociation (Ka), first order constant for the break down of the Michaelis complex (k + 2), and bimolecular rate (ka) were calculated as 6.38 × 10⁻⁵ M⁻¹ min⁻¹, 0.063 min⁻¹, and 9.83 × 10⁻⁴ M, respectively. Enzyme protection could be achieved with moderate butyrylthiocholine concentrations (0.3 mM) but higher concentrations increased CDDP inhibition. Apparent Ki value for CDDP was 191.8 ± 71.2 μM. These results suggest that used in combination therapy, CY and CDDP cause considerable BChE inhibition and may aggravate conditions observed during chemotherapy.     

A novel butyrylcholinesterase from serum of Leporinus macrocephalus, a Neotropical fish

We show here that serum of piaussu, a Neotropical characin fish, has the highest butyrylcholinesterase activity so far described for humans and fish. To clarify whether this cholinesterase could protect piaussu against anticholinesterase pesticides by scavenging organophosphates, we purified it 1700-fold, with a yield of 80%. Augmenting concentrations (from 0.01 to 20 mM) of butyrylthiocholine activated it. The pure enzyme was highly inhibited by chlorpyriphos-oxon (ki=10,434x10(6) M-1 min-1) and by the specific butyrylcholinesterase inhibitor, isoOMPA (ki=45.7x10(6) M-1 min-1). Electrophoresis of total serum and 2-D electrophoresis of the purified cholinesterase showed that some enzyme molecules could circulate in piaussu serum as heterogeneously glycosylated dimers. The enzyme's N-terminal sequence was similar to sequences found for butyrylcholinesterase from sera of other vertebrates. Altogether, our data present a novel butyrylcholinesterase with the potential of protecting a fish from poisoning by organophosphates.     

Dialkyl phenyl phosphates as novel selective inhibitors of butyrylcholinesterase

A series of dialkyl phenyl phosphates (DAPPs) were synthesized and evaluated in silico and in vitro for inhibitory activity against acetylcholinesterase and butyrylcholinesterase. Among the compounds examined, several DAPPs were shown to be potent inhibitors of butyrylcholinesterase, while having little activity against acetylcholinesterase. The most potent and selective inhibitors were di-n-butyl phenyl phosphate (K(i)=43 microM), di-n-pentyl phenyl phosphate (K(i)=6 microM), and di-cyclohexyl phenyl phosphate (K(i)=7 microM), the first which was shown to be a competitive inhibitor while the latter two being partial competitive inhibitors. Flexible docking simulations suggested that relative binding affinities generally increased as a function of alkyl chain length, while the strength and nature of inhibitory activity depended on whether the compound bound deeply or midway in the active site gorge, or in the proposed peripheral site.     

Pharmacological profile of MEN 11066, a novel potent and selective aromatase inhibitor

MEN 11066 is a new non-steroidal compound which potently inhibits human placenta (K_i=0.5 nM) and rat ovarian (K_i=0.2 nM) aromatase in vitro. In vivo, a single oral dose of 0.3 mg kg⁻¹ significantly decreased uterus weight in immature rats after stimulation of uterus growth by androstenedione. MEN 11066 reduced in a dose-dependent manner plasma estradiol levels in adult female rats treated with pregnant mare serum gonadotropin (PMSG). After 2 weeks of repeated daily treatment in adult rats, a significant decrease in uterine weight was observed together with a 65% decrease in plasma estradiol, whereas plasma levels of testosterone, progesterone, aldosterone, corticosterone, cholesterol, LH and FSH were not affected. The lack of any effect by MEN 11066 on adrenal steroids was confirmed by the unchanged plasma corticosterone and aldosterone levels in immature rats and also in adult rats when the repeated treatment with MEN 11066 (15 days) was followed by the administration of a synthetic ACTH analogue. No change in 11β-hydroxylase or 21-hydroxylase activities was produced in vitro by the addition of 10 μM MEN 11066. Fifteen-day treatment with MEN 11066 did not produce changes in several rat hepatic enzymatic activities involved in the metabolism of xenobiotics. These results demonstrated that MEN 11066 is a potent inhibitor of aromatase which does not interfere with the cytochrome P450 involved in the synthesis of other steroids or in the metabolism of xenobiotics.     

Whole body and tissue imaging of the butyrylcholinesterase knockout mouse injected with near infrared dye labeled butyrylcholinesterase

Butyrylcholinesterase (BChE) has proven to be an effective bioscavenger against nerve agents and organophosphates. Phase I safety trials of human BChE are currently being conducted and large-scale production of recombinant BChE is underway. Information on the real-time distribution of BChE from the injection site has not been well characterized. This study utilized the BChE nullizygote (BChE-/-) mouse and tetrameric equine BChE labeled with LI-COR((R)) fluorescent IRDye 800CW to track, quantify and determine the retention time of BChE in vivo following intramuscular injection. In vivo images were acquired with Xenogen's IVIS((R)) 200 imager and the LI-COR Odyssey((R)) Imaging System fitted with the MousePODtrade mark. Plasma and tissues were tested for BChE activity. The 2mg of BChE spread from the injection site to heart, liver, intestine, kidneys, lungs, salivary glands, and muscle, but did not enter the brain or the skin. Fluorescence intensity in organs and BChE activity in plasma peaked on day 1. BChE activity in plasma was undetectable by day 16, at a time when there was still significant fluorescent signal and BChE activity in the liver (0.32units/g), injected quadriceps (0.13units/g) and in most of the organs analyzed. It is concluded that the tetrameric BChE glycoprotein of 340kDa diffuses from the muscle injection site to blood and peripheral organs and has a longer residence time in the organs than in blood.     

The butyrylcholinesterase knockout mouse is obese on a high-fat diet

Butyrylcholinesterase (BChE) inactivates the appetite stimulating hormone octanoyl-ghrelin. The hypothesis was tested that BChE−/− mice would have abnormally high body weight and high levels of octanoyl-ghrelin. It was found that BChE−/− mice fed a standard 5% fat diet had normal body weight. However, BChE−/− mice fed a diet containing 11% fat became obese. Their obesity was not explained by increased levels of octanoyl-ghrelin, or by increased caloric intake, or by decreased exercise. Instead, a role for BChE in fat utilization was suggested.     

Development of potent reversible selective inhibitors of butyrylcholinesterase as fluorescent probes

Abstract

Brain butyrylcholinesterase (BChE) is an attractive target for drugs designed for the treatment of Alzheimer’s disease (AD) in its advanced stages. It also potentially represents a biomarker for progression of this disease. Based on the crystal structure of previously described highly potent, reversible, and selective BChE inhibitors, we have developed the fluorescent probes that are selective towards human BChE. The most promising probes also maintain their inhibition of BChE in the low nanomolar range with high selectivity over acetylcholinesterase. Kinetic studies of probes reveal a reversible mixed inhibition mechanism, with binding of these fluorescent probes to both the free and acylated enzyme. Probes show environment-sensitive emission, and additionally, one of them also shows significant enhancement of fluorescence intensity upon binding to the active site of BChE. Finally, the crystal structures of probes in complex with human BChE are reported, which offer an excellent base for further development of this library of compounds.     

Microcalorimetric study of the inhibition of butyrylcholinesterase by carbamates

The inhibition of horse serum butyrylcholinesterase (EC 3.1.1.8) by three carbamates (eserine, neostigmine, and rivastigmine) was studied by flow microcalorimetry at 37 degrees C in Tris buffer (pH 7.5). The kinetics of carbamylation was studied in the absence or presence of the substrate, butyrylcholine, using an extension of the model described by Stojan and coworkers (FEBS Lett. 440 (1998) 85-88). The model was fitted to the data by a nonlinear regression procedure using simulated annealing followed by Marquardt's method. The affinity of the carbamates for the free enzyme increased in the order neostigmine相似文献   

Mechanism of stereoselective interaction between butyrylcholinesterase and ethopropazine enantiomers

Stereoselectivity of reversible inhibition of butyrylcholinesterase (BChE; EC 3.1.1.8) by optically pure ethopropazine [10-(2-diethylaminopropyl)phenothiazine hydrochloride] enantiomers and racemate was studied with acetylthiocholine (0.002–250 mM) as substrate. Molecular modelling resulted in the reaction between BChE and ethopropazine starting with the binding of ethopropazine to the enzyme peripheral anionic site. In the next step ethopropazine ‘slides down’ the enzyme gorge, resulting in interaction of the three rings of ethopropazine through π–π interactions with W82 in BChE. Inhibition mechanism was interpreted according to three kinetic models: A, B and C. The models differ in the type and number of enzyme–substrate, enzyme–inhibitor and enzyme–substrate–inhibitor complexes, i.e., presence of the Michaelis complex and/or acetylated BChE. Although, all three models reproduced well the BChE activity in absence of ethopropazine, model A was poor in describing inhibition with ethopropazine, while models B and C were better, especially for substrate concentrations above 0.2 mM. However model C was singled out because it approaches fulfilment of the one step-one event criteria, and confirms the inhibition mechanism derived from molecular modelling. Model C resulted in dissociation constants for the complex between BChE and ethopropazine: 61, 140 and 88 nM for R-enantiomer, S-enantiomer and racemate, respectively. The respective dissociation constants for the complexes between acetylated BChE and ethopropazine were 268, 730 and 365 nM. Butyrylcholinesterase had higher affinity for R-ethopropazine.     

Microcalorimetric study of the inhibition of butyrylcholinesterase by paraoxon

The inhibition of horse serum butyrylcholinesterase (EC 3.1.1.8) by the organophosphorus compound paraoxon (diethyl 4-nitrophenyl phosphate) was studied by flow microcalorimetry at 37 °C in Tris buffer (pH 7.5) using a modification of the kinetic model described by Stojan and coworkers [J. Stojan, V. Marcel, S. Estrada-Mondaca, A. Klaebe, P. Masson, D. Fournier, A putative kinetic model for substrate metabolisation by Drosophila acetylcholinesterase, FEBS Lett. 440 (1998) 85-88]. The reversible steps of the inhibition were studied in the mixing cell of the calorimeter, whereas the irreversible step was studied in the flow-through cell. A new pseudo-first-order approximation was developed to allow the kinetic analysis of inhibition progress curves in the presence of substrate when a significant amount of substrate is transformed. This approximation also allowed one to compute an analytical expression of the calorimetric curves using a gamma distribution to describe the impulse response of the calorimeter. Fitting models to data by nonlinear regression, with simulated annealing as a stochastic optimization method, allowed the determination of all kinetic parameters. It was found that paraoxon binds to both the enzyme and acyl-enzyme, but with weak affinities (K_i = 0.123 mM and K′_i = 5.5 mM). A slight activation was observed at the lowest paraoxon concentrations and was attributed to the binding of the substrate to the enzyme-inhibitor complex. The bimolecular inhibition rate constant k_i = 2.8 × 10⁴ M⁻¹ s⁻¹ was in agreement with previous studies. It is hoped that the methods developed in this work will contribute to extending the application range of microcalorimetry in the field of irreversible inhibitors.     

Synthesis,biological evaluation and molecular modeling of substituted 2-aminobenzimidazoles as novel inhibitors of acetylcholinesterase and butyrylcholinesterase

A series of novel 2-aminobenzimidazole derivatives were synthesized under microwave irradiation. Their biological activities were evaluated on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A number of the 2-aminobenzimidazole derivatives showed good inhibitory activities to AChE and BuChE. Among them, compounds 9, 12 and 13 were found to be >25-fold more selective for BuChE than AChE. No evidence of cytotoxicity was observed by MTT assay in PC12 cells or HepG2 cells exposed to 100 μM of the compounds. Molecular modeling studies indicate that the benzimidazole moiety of compounds 9, 12 and 13 forms a face-to-face π–π stacking interaction in a ‘sandwich’ form with the indole ring of Trp82 (4.09 Å) in the active gorge, and compounds 12 and 13 form a hydrogen bond with His438 at the catalytic site of BuChE. In addition, compounds 12 and 13 fit well into the hydrophobic pocket formed by Ala328, Trp430 and Tyr332 of BuChE. Our data suggest the 2-aminobenzimidazole drugs as promising new selective inhibitors for AChE and BuChE, potentially useful to treat neurodegenerative diseases.     

The effects of Ni2+, Co2+, and Mn2+ on human serum butyrylcholinesterase

The effects of Ni2+, Co2+, and Mn2+ on human serum butyrylcholinesterase (BChE, acylcholine acylhydrolase E.C. 3.1.1.8) were investigated in this study. Inhibition kinetics of BChE were studied using butyrylthiocholine (BTCh) as substrate. The "1/v" versus "1/[BTCh]" plots in the absence (control plot) and in the presence of the metal ions intersected above 1/[BTCh]-axis for all trace elements. In addition, when the concentrations of the cations were increased at 4 mM BTCh, velocities decreased and drove to zero at high concentrations of the trace elements. These results demonstrate that Ni2+, Co2+, and Mn2+ are linear mixed-type inhibitors of BChE. alphaK(i) values have been determined as 53.20 mM,152.25 mM, and 190.24 mM for Ni2+, Mn2+, and Co2+, respectively, by using nonlinear regression analysis. From the comparison of alphaK(i) values of the trace elements, it can be said that BChE has more affinty to binding Ni2+ than Co2+ and Mn2+.     

Flow microcalorimetric study of butyrylcholinesterase kinetics and inhibition

The enzymatic hydrolysis of butyrylcholine, catalyzed by horse serum butyrylcholinesterase (EC 3.1.1.8), was studied at 37 degrees C in Tris buffer (pH 7.5) by flow microcalorimetry. A convolution procedure, using the Gamma distribution to represent the impulse response of the calorimeter, was developed to analyze the microcalorimetric curves. After correction for buffer protonation, the hydrolysis reaction was found to be slightly endothermic, with Delta H=+9.8 kJ mol(-1). Enzyme kinetics was studied with both the differential and integrated forms of the Michaelis equation with equivalent results: Michaelis constant K(m)=3.3mM, catalytic constant k(cat)=1.7 x 10(3)s(-1), bimolecular rate constant k(s)=5.1 x 10(5)M(-1)s(-1). The reaction product, choline, was found to be a competitive inhibitor with a dissociation constant K(i)=9.1mM. Betaine had a slightly higher affinity for the enzyme, but the inhibition was only partial. This study confirms the usefulness of microcalorimetry for the kinetic study of enzymes and their inhibitors.     

Effects of a new synthetic butyrylcholinesterase inhibitor, HBU-39, on cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus in a scopolamine-induced amnesia animal model

In this study, we synthesized [1-(4-(benzo[d][1,3]dioxol-5-ylmethyl)piperazin-1-yl)-5-(1,2-dithiolan-3-yl)pentan-1-one, HBU-39], a (α)-lipoic acid derivative, and found this compound strongly inhibited butyrylcholinesterase (BuChE) in an in vitro experiment. We also examined the effects of HBU-39 on cell proliferation and neuroblast differentiation using the specific markers Ki67 and doublecortin (DCX), respectively, in the hippocampal dentate gyrus of a rat model of scopolamine-induced amnesia. For this, scopolamine was subcutaneously administered for 28 days by an ALzet osmotic minipump (44 mg/mL delivered at 2.5 μL/h). HBU-39 (1 mg/kg per day) and galantamine (an acetylcholinesterase inhibitor used as a control; 5 mg/kg per day) were intraperitoneally administered for 28 days. The administration of scopolamine significantly decreased the mean number of Ki67- and DCX-immunoreactive cells in the dentate gyrus. However, treatment with both HBU-39 and galantamine significantly ameliorated the reductions in cell proliferation and neuroblast differentiation. In particular, the mean number of Ki67- and DCX-immunoreactive cells was prominently abundant in the HBU-treated group compared to that in the galantamine-treated group. These results suggest that the BuChE inhibitor, HBU-39, can ameliorate the scopolamine-induced reductions of cell proliferation and neuroblast differentiation, and HBU-39 may be applicable to amnesia patients to promote memory functions.     

3-Amidoquinuclidine derivatives: synthesis of compounds and inhibition of butyrylcholinesterase

The synthesis of racemic and enantiomerically pure 3-butanamidoquinuclidines ((+/-)-Bu, (R)-Bu and (S)-Bu), (1-3) and 3-benzamidoquinuclidines ((+/-)-Bz, (R)-Bz, and (S)-Bz), (4-6) is described. The N-quaternary derivatives, N-benzyl-3-butanamidoquinuclidinium bromides ((+/-)-BnlBu, (R)-BnlBu and (S)-BnlBu), (7-9) and N-benzyl-3-benzamidoquinuclidinium bromides ((+/-)-BnlBz, (R)-BnlBz and (S)-BnlBz), (10-12) were subsequently synthesized. The interaction of the four enantiomerically pure quaternary derivatives with horse serum butyrylcholinesterase (BChE) was tested. All tested compounds inhibited the enzyme. The best inhibitior of the enzyme was (S)-BnlBz with a K(i) = 3.7 microM. The inhibitor potency decreases in order (S)-BnlBz > (R)-BnlBz > (R)-BnlBu > (S)-BnlBu.     

Lipsome-formulated enzymes for organophosphate scavenging: butyrylcholinesterase and Demeton-S

Butyrylcholinesterase-encapsulating bioadhesive liposomes are investigated as prophylactic scavengers of organophosphates for local administration to skin, eyes, airways, and lungs-gates through which organophosphates penetrate living systems. The systems were optimized with respect to: encapsulation efficiency; type of bioadhesive ligand bound to liposomes (collagen or hyaluronan); ligand density at the liposomal surface; retention of encapsulated-enzyme activity; protection of encapsulated enzyme from proteolysis; and scavenging the model organophosphate Demeton-S (DS). Monolayers of PC-12 cells were selected for feasibility testing based on: high affinity binding of the bioadhesive liposomes-DeltaG0 release upon binding ranged from -9 to -12 kcal/mol ligand; ability to mimic an organophosphate attack upon intact cells and measuring its impact on intracellular acetylcholinesterase. Under attack, unprotected cells lost 80-90% of intracellular enzyme activity. The loss was reduced to 20-30% for protected cells (pre-treated with the formulations), at the expense of liposomal Butyrylcholinesterase. These results support our prophylactic approach.     

Design and synthesis of N-benzylpiperidine-purine derivatives as new dual inhibitors of acetyl- and butyrylcholinesterase

The synthesis and biological evaluation of N-benzyl-(piperidin or pyrrolidin)-purines are described. Compounds derived from N-benzylpiperidine and N-substituted purines showed moderate acetylcholinesterase inhibition. Preliminary structure–activity relationships and a superimposition of the best compound with the active conformation of donepezil have revealed structural features that have been used in the design of more potent N-benzylpiperidine inhibitors bearing an 8-substituted caffeine fragment and a methoxymethyl linker. These new compounds are interesting dual inhibitors of acetylcholinesterase and butyrylcholinesterase and have been chosen for further optimisation.     

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 2× LD₅₀ 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 0.05–0.2 M 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.     

Increased serum butyrylcholinesterase activity in type IIb hyperlipidaemic patients

The inheritance of the apolipoprotein E4 (APOE4) allele has been shown to increase the plasma cholesterol level, but little information is as concerns the association of the APOE genotype and hyperlipidaemia and the activities of two serum enzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Blood samples from 55 type IIb hyperlipidaemic, non-demented patients and 55 age- and sex-matched controls were therefore examined in this pilot study. A significantly increased BChE activity was found in the serum of type IIb hyperlipidaemic patients, but the AChE activity did not differ significantly as compared with that in the control group. The APOE4 allele was significantly overrepresented among the hyperlipidaemic probands, but neither serum cholinesterase activity was affected by the dosage of the APOE4 gene. Our results point to a possible association between an abnormal lipid metabolism and the BChE activity and might have implications as regards the pathomechanism of both Alzheimer's and vascular dementias and the cholinesterase inhibitor therapy of dementing disorders.     

A new perspective on thermal inactivation kinetics of human serum butyrylcholinesterase

Butyrylcholinesterase purified from human serum as 6600-fold was heated at 37°, 40°, 45°, and 50°C for 24 hr. It was observed that the enzyme heated at 45°C for 24 hr converted to a stabilized form and followed Michaelis-Menten kinetics, whereas the enzyme samples, heated at the other temperatures for 24 hr, shown negative cooperativity with respect to its substrate, butyrylthiocholine. Even the sample heated at 45°C for 12 hr shown negative cooperativity. On the contrary to the heated enzyme at 40°C for 24 hr, the heated enzyme at 45°C for 24 hr could not be reactivated when it was kept at 4°C for 24 hr. In the kinetic studies, it was found that substrate analogs choline and benzoylcholine inhibited both the native enzyme and the enzyme heated at 45°C for 24 hr competitively, whereas succinylcholine was the partial competitive inhibitor of native enzyme but the pure competitive inhibitor of the heated enzyme.