Substance P Hydrolysis by Human Serum Cholinesterase

Highly purified human serum cholinesterase (EC 3.1.1.8, also known as pseudocholinesterase and butyrylcholinesterase) had peptidase activity toward substance P. Digestion of substance P was monitored by high performance liquid chromatography, which separated three product peptides. The cleavages occurred sequentially. The first peptide to appear was Arg 1 -Pro 2 . The K m for this hydrolysis was 0.3 m M ; maximum activity was 7.9 nmol min −1 mg −1 of protein, which corresponded to a turnover number of 0.6 min −1 . A second cleavage yielded Lys 3 -Pro 4 . A third cleavage occurred at the C-terminal, where the amide was removed from Met 11 to yield a peptide containing residues 5–11. Both the peptidase and esterase activities of the enzyme were completely inhibited by the anticholinesterase agent, diisopropyl-fluorophosphate. Substance P inhibited the hydrolysis of benzoylcholine (a good ester substrate) with a K I of 0.17 m M , indicating that substance P interacted with cholinesterase rather than with a trace contaminant. Peptidase and amidase activities for serum cholinesterase are novel activities for this enzyme. It was demonstrated previously that the related enzyme acetylcholinesterase (EC 3.1.1.7) catalyzed the hydrolysis of substance P, but at entirely different cleavage sites from those reported in the present work. Since butyrylcholinesterase is present in brain and muscle, as well as in serum, it may be involved in the physiological regulation of substance P.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66407/1/j.1471-4159.1982.tb04707.x.pd

Butyrylcholinesterase genotype and enzyme activity in relation to Gulf War illness: preliminary evidence of gene-exposure interaction from a case¿control study of 1991 Gulf War veterans

Abstract Background Epidemiologic studies have implicated wartime exposures to acetylcholinesterase (AChE)-inhibiting chemicals as etiologic factors in Gulf War illness (GWI), the multisymptom condition linked to military service in the 1991 Gulf War. It is unclear, however, why some veterans developed GWI while others with similar exposures did not. Genetic variants of the enzyme butyrylcholinesterase (BChE) differ in their capacity for metabolizing AChE-inhibiting chemicals, and may confer differences in biological responses to these compounds. The current study assessed BChE enzyme activity and BChE genotype in 1991 Gulf War veterans to evaluate possible association of this enzyme with GWI. Methods This case–control study evaluated a population-based sample of 304 Gulf War veterans (144 GWI cases, meeting Kansas GWI criteria, and 160 controls). BChE enzyme activity levels and genotype were compared, overall, in GWI cases and controls. Potential differences in risk associated with cholinergic-related exposures in theater were explored using stratified analyses to compare associations between GWI and exposures in BChE genetic and enzyme activity subgroups. Results Overall, GWI cases and controls did not differ by mean BChE enzyme activity level or by BChE genotype. However, for the subgroup of Gulf War veterans with less common, generally less active, BChE genotypes (K/K, U/AK, U/A, A/F, AK/F), the association of wartime use of pyridostigmine bromide (PB) with GWI (OR = 40.00, p = 0.0005) was significantly greater than for veterans with the more common U/U and U/K genotypes (OR = 2.68, p = 0.0001). Conclusions Study results provide preliminary evidence that military personnel with certain BChE genotypes who used PB during the 1991 Gulf War may have been at particularly high risk for developing GWI. Genetic differences in response to wartime exposures are potentially important factors in GWI etiology and should be further evaluated in conjunction with exposure effects.Peer Reviewe

Prediction of drug sensitivity in individuals with atypical serum cholinesterase based on in vitro biochemical studies

Vmax and Km values with twenty-five "atypical" and thirty-seven "usual" cholinesterase human sera were determined for the cholinesterase substrates procaine, tetracaine, benzoylcholine, o-nitro-phenylbutyrate, [alpha]-naphthylacetate and aspirin. Aspirin was demonstrated to be a substrate for serum cholinesterase. For each of these substrates the ratio of Vmax substrate to Vmax benzoylcholine was found to be similar with atypical and usual cholinesterase sera. Therefore, we concluded that the respective turnover numbers for atypical and usual cholinesterase were the same. Both atypical and usual cholinesterase sera had turnover numbers of 255 min-1 for procaine, 74 min-1 for tetracaine, 7200 min-1 for aspirin in the presence of 50 mM CaCl2 36,000 min-1 for [alpha]-naphthylacetate, and 48,000 min-1 for o-nitrophenylbutyrate, at 25[deg] in 0.1 M Tris-Cl buffer, pH 7.4. A comparison of Km values for atypical and usual cholinesterase indicated that the positively charged substrates, as well as aspirin in the presence of CaCl2, showed a lower affinity with atypical than with usual cholinesterase, while neutral esters had nearly the same Km for atypical and usual cholinesterase. These results imply that individuals with atypical cholinesterase will hydrolyze therapeutic doses of positively charged substrates and aspirin at reduced rates, but neutral substrates should be hydrolyzed at normal rates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24348/1/0000615.pd

Proposed nomenclature for human butyrylcholinesterase genetic variants identified by DNA sequencing

1. New information identifying nucleotide alterations of human butyrylcholinesterase allows the use of more specific nomenclature for the variants commonly known as atypical, fluoride, silent, and K variant.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44278/1/10571_2004_Article_BF00712801.pd

Gene-delivered butyrylcholinesterase is prophylactic against the toxicity of chemical warfare nerve agents and organophosphorous

ABSTRACT Gene delivery using an adenoviral system has been effective in introducing therapeutic proteins in vitro and in vivo. This study tested the feasibility of using adenovirus to deliver clinically relevant amounts of butyrylcholinesterase (BChE), a proven bioscavenger of nerve agents. The adenovirus construct expressed full-length mouse BChE. Mice were injected with a single dose of adenovirus (1.5 ϫ 10 10 infectious units) in the tail vein; plasma was collected through day 11 and assayed for BChE activity. Maximum activity, representing a 300-to 3400-fold increase over baseline, was found on day 4. Expression levels returned to baseline by day 10. Nondenaturing gel electrophoresis showed the recombinant BChE was a dimer that could be converted to tetramers by addition of polyproline. The toxic compounds chosen for protection studies were positively charged organophosphorus agents, echothiophate, and O-ethyl-S-2-N,N-diisopropylaminoethyl methylphosphonothiolate (VX). Mice containing elevated blood levels of BChE (300-to 3,000-fold over the control mice) were challenged with incremental doses of echothiophate or VX. Mice showed no signs of toxicity and were protected from up to 30ϫ LD 50 dose of echothiophate and 5ϫ LD 50 dose of VX. A good correlation was observed between tolerated echothiophate dose and plasma BChE levels at time of challenge. The absolute increases in levels of circulating BChE and the sustained nature of the response resulted in a very high enzyme concentration, deemed critical in acute toxicity (5ϫ LD 50 or more) scenarios. These results suggest that gene-delivered BChE is a prophylactic and affords protection equivalent to that of a multimilligram injection of the same

The cloned butyrylcholinesterase (BCHE) gene maps to a single chromosome site, 3q26

Human tissues have two distinct cholinesterase activities: acetylcholinesterase and butyrylcholinesterase. Acetylcholinesterase functions in the transmission of nerve impulses, whereas the physiological function of butyrylcholinesterase remains unknown. An atypical form of butyrylcholinesterase or the absence of its activity leads to prolonged apnea following administration of the muscle relaxant suxamethonium. Inheritance of these butyrylcholinesterase variants is consistent with the enzyme activity being encoded in a single autosomal locus, BCHE (formerly CHE1 and E1), which has been assigned to chromosome 3. Previous in situ hybridization of a BCHE cDNA probe gave evidence of homologous sequences at 3q26 and 16q11-q23, raising the possibility of more than one locus coding for butyrylcholinesterase [20.] Hum. Genet. 77: 325-328]. Using a different cDNA probe hybridized in situ to 46,XX,inv(3)(p25q21) metaphase chromosomes, we report here the localization of BCHE to a single autosomal location: 3q26.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29109/1/0000147.pd

Loss of Dnmt3b function upregulates the tumor modifier Ment and accelerates mouse lymphomagenesis

DNA methyltransferase 3B (Dnmt3b) belongs to a family of enzymes responsible for methylation of cytosine residues in mammals. DNA methylation contributes to the epigenetic control of gene transcription and is deregulated in virtually all human tumors. To better understand the generation of cancer-specific methylation patterns, we genetically inactivated Dnmt3b in a mouse model of MYC-induced lymphomagenesis. Ablation of Dnmt3b function using a conditional knockout in T cells accelerated lymphomagenesis by increasing cellular proliferation, which suggests that Dnmt3b functions as a tumor suppressor. Global methylation profiling revealed numerous gene promoters as potential targets of Dnmt3b activity, the majority of which were demethylated in Dnmt3b–/– lymphomas, but not in Dnmt3b–/– pretumor thymocytes, implicating Dnmt3b in maintenance of cytosine methylation in cancer. Functional analysis identified the gene Gm128 (which we termed herein methylated in normal thymocytes [Ment]) as a target of Dnmt3b activity. We found that Ment was gradually demethylated and overexpressed during tumor progression in Dnmt3b–/– lymphomas. Similarly, MENT was overexpressed in 67% of human lymphomas, and its transcription inversely correlated with methylation and levels of DNMT3B. Importantly, knockdown of Ment inhibited growth of mouse and human cells, whereas overexpression of Ment provided Dnmt3b+/+ cells with a proliferative advantage. Our findings identify Ment as an enhancer of lymphomagenesis that contributes to the tumor suppressor function of Dnmt3b and suggest it could be a potential target for anticancer therapies

Protein tyrosine adduct in humans self-poisoned by chlorpyrifos

Studies of human cases of self-inflicted poisoning suggest that chlorpyrifos oxon reacts not only with acetylcholinesterase and butyrylcholinesterase but also with other blood proteins. A favored candidate is albumin because in vitro and animal studies have identified tyrosine 411 of albumin as a site covalently modified by organophosphorus poisons. Our goal was to test this proposal in humans by determining whether plasma from humans poisoned by chlorpyrifos has adducts on tyrosine. Plasma samples from 5 self-poisoned humans were drawn at various time intervals after ingestion of chlorpyrifos for a total of 34 samples. All 34 samples were analyzed for plasma levels of chlorpyrifos and chlorpyrifos oxon (CPO) as a function of time post-ingestion. Eleven samples were analyzed for the presence of diethoxyphosphorylated tyrosine by mass spectrometry. Six samples yielded diethoxyphosphorylated tyrosine in pronase digests. Blood collected as late as 5 days after chlorpyrifos ingestion was positive for CPO-tyrosine, consistent with the 20-day half-life of albumin. High plasma CPO levels did not predict detectable levels of CPO-tyrosine. CPO-tyrosine was identified in pralidoxime treated patients as well as in patients not treated with pralidoxime, indicating that pralidoxime does not reverse CPO binding to tyrosine in humans. Plasma butyrylcholinesterase was a more sensitive biomarker of exposure than adducts on tyrosine. In conclusion, chlorpyrifos oxon makes a stable covalent adduct on the tyrosine residue of blood proteins in humans who ingested chlorpyrifos

Methamidophos, Dichlorvos, O-Methoate And Diazinon Pesticides Used In Turkey Make A Covalent Bond With Butyrylcholinesterase Detected By Mass Spectrometry

Organophosphorus pesticides used most commonly in Turkey include methamidophos, dichlorvos, O-methoate and diazinon. These toxic chemicals or their metabolites make a covalent bond with the active site serine of butyrylcholinesterase. Our goal was to identify the adducts that result from the reaction of human butyrylcholinesterase with these pesticides. Highly purified human butyrylcholinesterase was treated with a 20-fold molar excess of pesticide. The protein was denatured by boiling and digested with trypsin. MS and MSMS spectra of HPLC-purified peptides were acquired on a MALDI-TOF-TOF 4800 mass spectrometer. It was found that methamidophos added a mass of +93, consistent with addition of methoxy aminophosphate. A minor amount of adduct with an added mass of +109 was also found. Dichlorvos and O-methoate both made dimethoxyphosphate (+108) and monomethoxyphosphate adducts (+94). Diazinon gave a novel adduct with an added mass of +152 consistent with diethoxythiophosphate. Inhibition of enzyme activity in the presence of diazinon developed slowly (15 h), concomitant with isomerization of diazinon via a thiono-thiolo rearrangement. The isomer of diazinon yielded diethoxyphosphate and monoethoxyphosphate adducts with added masses of +136 and +108. MSMS spectra confirmed that each of the pesticides studied made a covalent bond with serine 198 of butyrylcholinesterase. These results can be used to identify the class of pesticides to which a patient was exposed. Copyright (C) 2010 John Wiley & Sons, Ltd.Wo