Why has butyrylcholinesterase been retained? Structural and functional diversification in a duplicated gene

Reduced vagal control of the heart in high-fat diet mice: a potential role of increased butyrylcholinesterase

Suppressed parasympathetic function is commonly present in cardiovascular diseases, aging, obesity, and various other health conditions. Impaired parasympathetic action is known as a detrimental factor and contributes to the adverse outcomes in these conditions. However, the underlying mechanisms remain to be fully addressed. In this study, using high-fat diet (HFD)-induced obese mice as a model, the potential peripheral mechanisms underlying the impaired parasympathetic vagal control of the heart was examined. The HFD induced obesity and metabolic disorder in mice. These obese mice exhibited an attenuated response in heart rate to vagal stimulation, indicating impairment of peripheral parasympathetic activity in the heart. In cholinergic function-related proteins in the atria, protein levels of choline transporter and vesicular acetylcholine transporter were not decreased but increased, and type 2 muscarinic receptors showed a trend toward a reduction in HFD mice atria as compared with regular diet (RD) mice controls. While the protein level of acetylcholinesterase was not different, butyrylcholinesterase (BChE) protein level showed a twofold increase in HFD mice atria as compared with RD mice. Functionally, inhibition of BChE activity partially and significantly improved the attenuated response in heart rate to vagal stimulation in HFD mice. Collectively, these data suggest that increased BChE activity in the atria may contribute to the decreased parasympathetic function in HFD-induced obese mice.

New Insights into Butyrylcholinesterase Activity Assay: Serum Dilution Factor as a Crucial Parameter

Butyrylcholinesterase (BChE) activity assay and inhibitor phenotyping can help to identify patients at risk of prolonged paralysis following the administration of neuromuscular blocking agents. The assay plays an important role in clinical chemistry as a good diagnostic marker for intoxication with pesticides and nerve agents. Furthermore, the assay is also commonly used for in vitro characterization of cholinesterases, their toxins and drugs. There is still lack of standardized procedure for measurement of BChE activity and many laboratories use different substrates at various concentrations. The purpose of this study was to validate the BChE activity assay to determine the best dilution of human serum and the most optimal concentration of substrates and inhibitors. Serum BChE activity was measured using modified Ellman’s method applicable for a microplate reader. We present our experience and new insights into the protocol for high-throughput routine assays of human plasma cholinesterase activities adapted to a microplate reader. During our routine assays used for the determination of BChE activity, we have observed that serum dilution factor influences the results obtained. We show that a 400-fold dilution of serum and 5mM S-butyrylthiocholine iodide can be successfully used for the accurate measurement of BChE activity in human serum. We also discuss usage of various concentrations of dibucaine and fluoride in BChE phenotyping. This study indicates that some factors of such a multicomponent clinical material like serum can influence kinetic parameters of the BChE. The observed inhibitory effect is dependent on serum dilution factor used in the assay.

Butyrylcholinesterase predicts cardiac mortality in young patients with acute coronary syndrome

Background

The incidence of acute coronary syndrome (ACS) in young people (≤65 years) is continuously rising. While prognostic factors in ACS are well-investigated less attention has been paid to their age-dependent prognostic value and their particular relevance in younger patients. The aim of our study was to assess the age-dependent prognostic impact of butyrylcholinesterase (BChE).

Methods

Retrospective cohort study including 624 patients with ACS. Patients were stratified by age into equal groups (n = 208) corresponding to “young patients” (45–64 years), "middle-aged patients” (65–84 years) and “old patients” (85–100 years). Cox regression hazard analysis was used to assess the influence of BChE on survival.

Results

After a mean follow-up time of 4.0 (interquartile range [IQR] 2.0–6.4) years, 154 patients (24.7%) died due to a cardiac cause. In the overall cohort, BChE was indirectly associated with cardiac mortality-free survival (adjusted hazard ratio (HR): 0.70 (95% confidence interval [CI] 0.53–0.93, p = 0.01). The primary-analysis of BChE by age strata showed the strongest effect in the age group 45–64 years with an adjusted HR per 1-SD of 0.28 (95% CI 0.12–0.64, p = 0.003), a weaker association with mortality in middle aged (65–84 years: adjusted HR per 1-SD 0.66 [95% CI: 0.41–1.06], p = 0.087), and no association in older patients (85–100 years: adjusted HR per 1-SD 0.89 [95% CI: 0.58–1.38], p = 0.613).

Conclusion

BChE is a strong predictor for cardiac mortality specifically in younger patients with ACS aged between 45 and 64 years. No significant association of BChE with cardiac-mortality was detected in other age classes.

Butyrylcholinesterase: K variant, plasma activity, molecular forms and rivastigmine treatment in Alzheimer's disease in a Southern Brazilian population

Alzheimer's disease (AD) is a neurodegenerative disorder in which there is a decline of cholinergic function. The symptomatic AD treatment involves the use of ChEIs (cholinesterase inhibitors) as rivastigimine, a dual inhibitor. The human butyrylcholinesterase (BChE) is an enzyme that has specific roles in cholinergic neurotransmission and it has been associated with AD. In the serum, BChE is found in four main molecular forms: G1 (monomer); G1-ALB (monomer linked to albumin); G2 (dimer); and G4 (tetramer). The interaction between the products of BCHE gene and CHE2 locus results in CHE2 C5+ and CHE2 C5- phenotypes. CHE2 C5+ phenotype and BChE-K are factors that influence on BChE activity. This work aimed to verify the proportions of BChE molecular forms, total and relative activity in 139 AD patients and 139 elderly controls, taking into account K variant, CHE2 locus, rivastigmine treatment and clinical dementia rating (CDR) of AD patients. Phenotypic frequencies of CHE2 C5+ and frequency of the carriers of the K allele were similar between groups. Total BChE activity in plasma was significantly lower in AD patients than in elderly controls. Furthermore, we found that reduction on plasma BChE activity is associated directly with AD progression in AD patients and that rivastigmine treatment has a stronger effect on BChE activity within the CDR2 group. The reduction in BChE activity did not occur proportionally in all molecular forms. Multiple regression analysis results confirmed that AD acts as the main factor in plasma BChE activity reduction and that severe stages are related with an even greater reduction. These findings suggest that the reduction of total plasma BChE and relative BChE molecular forms activity in AD patients is probably associated with a feedback mechanism and provides a future perspective of using this enzyme as a possible plasmatic secondary marker for AD.

Molecular characterization of an acetylcholinesterase from the hemichordate Saccoglossus kowalevskii

Our goal is to understand the evolution of the structure and function of cholinesterases (ChEs) in the deuterostome lineage and in particular to understand the role of paralogous enzymes such as the acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) of the vertebrates. We have, in the past, characterized ChEs in two acraniate deuterostomes: amphioxus (a cephalochordate) and Ciona intestinalis (a urochordate). Here we present results on an AChE from a basal deuterostome, a model hemichordate, the acorn worm Saccoglossus kowalevskii. Of the eight genes coding for putative ChE-like proteins possessing Trp84, a characteristic of the choline-binding catalytic subsite of ChEs, we cloned a full length cDNA with a coding sequence typical of an acraniate AChE possessing a C-terminal exon coding for a typical T-peptide. We then used in vitro expression of the cDNA in COS-7 cells to characterize the AChE kinetically, pharmacologically, and biochemically. The cDNA codes for an AChE (AChE1), which is found in monomeric (G1), dimeric (G2), and tetrameric (G4) forms; and interacts with poly-L-proline, PRiMA, and ColQ, characteristic of an AChE possessing a T-peptide. The expression of the AChE is temperature dependent, with greater expression at 30 °C. We discuss the implications of these data for the evolution of the ChEs in the deuterostomes.

Characterization of placental cholinesterases and activity induction associated to environmental organophosphate exposure

Although non-innervated, the placenta contains both cholinesterases (ChEs), butyrylcholinesterase (BChE) and acetylcholinesterase (AChE). These enzymes are well-known for their multiple molecular forms. In a first approach, we used recognized specific inhibitors, substrate preferences and non-denaturating gel electrophoresis in order to characterize the ChE profile of term placenta from uncomplicated pregnancy. Results strongly suggest that the predominant cholinesterasic form present was tetrameric BChE. It is well established that both ChEs are targets of cholinesterase-inhibiting organophosphates (OP), one of the most important classes of chemicals actively applied to the environment. However, we have previously reported increased ChEs activity in placenta of rural residents exposed to OP. In the present work, we have studied: 1) whether this finding was reproducible and, 2) whether AChE or BChE up regulation is behind the increase of placental ChE activity. The population studied included forty healthy women who live in an agricultural area. Samples were collected during both the OP pulverization period (PP) and the recess period (RP). The placental ChEs activity increased in PP, evidencing reproducibility of previous results. The analysis of non-denaturating gels revealed that increased activity of total ChE activity in placenta from women exposed to OP may be attributable to tetrameric BChE up-regulation.

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.

Schwann cells sense and control acetylcholine spillover at the neuromuscular junction by α7 nicotinic receptors and butyrylcholinesterase

Terminal Schwann cells (TSCs) are key components of the mammalian neuromuscular junction (NMJ). How the TSCs sense the synaptic activity in physiological conditions remains unclear. We have taken advantage of the distinct localization of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at the NMJ to bring out the function of different ACh receptors (AChRs). AChE is clustered by the collagen Q in the synaptic cleft and prevents the repetitive activation of muscle nicotinic AChRs. We found that BChE is anchored at the TSC by a proline-rich membrane anchor, the small transmembrane protein anchor of brain AChE. When BChE was specifically inhibited, ACh release was significant depressed through the activation of α7 nAChRs localized on the TSC and activated by the spillover of ACh. When both AChE and BChE were inhibited, the spillover increased and induced a dramatic reduction of ACh release that compromised the muscle twitch triggered by the nerve stimulation. α7 nAChRs at the TSC may act as a sensor for spillover of ACh adjusted by BChE and may represent an extrasynaptic sensor for homeostasis at the NMJ. In myasthenic rats, selective inhibition of AChE is more effective in rescuing muscle function than the simultaneous inhibition of AChE and BChE because the concomitant inhibition of BChE counteracts the positive action of AChE inhibition. These results show that inhibition of BChE should be avoided during the treatment of myasthenia and the pharmacological reversal of residual curarization after anesthesia.

Characterization of a novel butyrylcholinesterase point mutation (p.Ala34Val), "silent" with mivacurium

Butyrylcholinesterase deficiency is characterized by prolonged apnea after the use of muscle relaxants (suxamethonium or mivarcurium) in patients who have mutations in the BCHE gene. Here, we report a case of prolonged neuromuscular block after administration of mivacurium leading to the discovery of a novel BCHE variant (c.185C>T, p.Ala34Val). Inhibition studies, kinetic analysis and molecular dynamics were undertaken to understand how this mutation remote from the active center determines the "silent" phenotype. Low activity of patient plasma butyrylcholinesterase with butyrylthiocholine (BTC) and benzoylcholine, and values of dibucaine and fluoride numbers fit with a heterozygous enzyme of type atypical/silent. Kinetic analysis with succinyldithiocholine (SCdTC) as the substrate showed that Ala34Val BChE was inactive against this substrate. However, with BTC, the mutant enzyme was active, displaying an unexpected activation by excess substrate. Competitive inhibition of BTC by mivacurium gave a Ki=1.35 mM consistent with the lack of activity with the related substrate SCdTC, and with the clinical data. Molecular dynamic simulations revealed the mechanism by which mutation Ala34Val determines the silent phenotype: a chain of intramolecular events leads to disruption of the catalytic triad, so that His438 no longer interacts with Ser198, but instead forms hydrogen bonds either with residues Glu197 and Trp82, or peripheral site residue Tyr332. However, at high BTC concentration, initial binding of substrate to the peripheral site triggers restoration of a functional catalytic triad, and activity with BTC.

Characterization of a novel BCHE "silent" allele: point mutation (p.Val204Asp) causes loss of activity and prolonged apnea with suxamethonium

Butyrylcholinesterase deficiency is characterized by prolonged apnea after the use of muscle relaxants (suxamethonium or mivacurium) in patients who have mutations in the BCHE gene. Here, we report a case of prolonged neuromuscular block after administration of suxamethonium leading to the discovery of a novel BCHE variant (c.695T>A, p.Val204Asp). Inhibition studies, kinetic analysis and molecular dynamics were undertaken to understand how this mutation disrupts the catalytic triad and determines a “silent” phenotype. Low activity of patient plasma butyrylcholinesterase with butyrylthiocholine (BTC) and benzoylcholine, and values of dibucaine and fluoride numbers fit with heterozygous atypical silent genotype. Electrophoretic analysis of plasma BChE of the proband and his mother showed that patient has a reduced amount of tetrameric enzyme in plasma and that minor fast-moving BChE components: monomer, dimer, and monomer-albumin conjugate are missing. Kinetic analysis showed that the p.Val204Asp/p.Asp70Gly-p.Ala539Thr BChE displays a pure Michaelian behavior with BTC as the substrate. Both catalytic parameters K_m = 265 µM for BTC, two times higher than that of the atypical enzyme, and a low V_max are consistent with the absence of activity against suxamethonium. Molecular dynamic (MD) simulations showed that the overall effect of the mutation p.Val204Asp is disruption of hydrogen bonding between Gln223 and Glu441, leading Ser198 and His438 to move away from each other with subsequent disruption of the catalytic triad functionality regardless of the type of substrate. MD also showed that the enzyme volume is increased, suggesting a pre-denaturation state. This fits with the reduced concentration of p.Ala204Asp/p.Asp70Gly-p.Ala539Thr tetrameric enzyme in the plasma and non-detectable fast moving-bands on electrophoresis gels.

Rosmarinus officinalis L. leaf extract improves memory impairment and affects acetylcholinesterase and butyrylcholinesterase activities in rat brain

Rosmarinus officinalis L. leaf as part of a diet and medication can be a valuable proposal for the prevention and treatment of dementia. The aim of the study was to assess the effects of subchronic (28-fold) administration of a plant extract (RE) (200 mg/kg, p.o.) on behavioral and cognitive responses of rats linked with acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity and their mRNA expression level in the hippocampus and frontal cortex. The passive avoidance test results showed that RE improved long-term memory in scopolamine-induced rats. The extract inhibited the AChE activity and showed a stimulatory effect on BuChE in both parts of rat brain. Moreover, RE produced a lower mRNA BuChE expression in the cortex and simultaneously an increase in the hippocampus. The study suggests that RE led to improved long-term memory in rats, which can be partially explained by its inhibition of AChE activity in rat brain.