Effects of storage and repeated freezing and thawing on plasma cholinesterase activity

Serum butyrylcholinesterase activity in healthy dogs with and without exposure to diazinon

BACKGROUND

Cholinesterase is a biomarker for poisonings by anticholinesterase agents, but its reference values are scarce, and possible interaction with collars containing parasiticides has not been studied.

OBJECTIVES

We aimed to evaluate the serum cholinesterase activity of healthy dogs without a history of contact with anticholinesterase agents and healthy animals exposed to commercial collars containing organophosphate.

METHODS

Ninety-nine dogs were used and included healthy animals without recent exposure to anticholinesterase agents and healthy animals previously exposed to diazinon collars. Serum quantification of the enzyme butyrylcholinesterase (BuchE) through spectrophotometry was conducted on all samples. In experiment 1, BuchE activity was quantified at time 0 and 7 days after, a time when the samples were kept at -18°C. In experiment 2, sampling times were 0, 7, 14, 21, 28, and 56 days.

RESULTS

Time 0 values were 4622.38 ± 1311.53 U/L. After 7 days, a significant decay was observed, with a mean of 3934.45 ± 1430.45 U/L. Spearman's test was performed, finding a weak correlation between ALT, creatinine, total plasma proteins, age, weight, red blood cells, platelets, leukocytes, and BuchE activities. In experiment 2, the mean at time 0 was 4753 ± 454.8 U/L. With exposure to the collar, there was a decay of up to 93% after 14 days.

CONCLUSIONS

Normality values of serum BuchE in healthy dogs without a history of exposure to anticholinesterase agents were 4360.8-4883.96 U/L. Freezing serum caused a decrease in BuchE activity. Exposure to commercial collars containing diazinon also reduced BuchE activity without clinical signs, indicating that previously exposed animals should be evaluated carefully.

Time-dependent effects of storage at -80 °C on the stability of butyrylcholinesterase activity in human serum

Objectives

Butyrylcholinesterase (BChE) is an important biomarker in serum, and aberrant BChE activity indicates onset and progression of human diseases. The duration of serum storage at −80 °C may introduce variability into and compromise the reproducibility of BChE activity measurements.

Design and Methods

We collected serum samples from eight healthy volunteers and determined serum BChE activity in these samples using a sensitive fluorescence assay at various time points during a six-month storage period at −80 °C. Changes in averaged BChE activity over storage time were assessed by repeated measures analysis of variance (ANOVA). Sidak multiple comparisons test was also used to perform post-hoc analysis.

Results

Almost all determined BChE activity values lay within the normal physiological range of BChE activity. However, repeated measures ANOVA using mean BChE activity vs. storage time showed that BChE activity values from two time points were significantly different. Analysis by Sidak multiple comparisons test provided no substantial change of BChE activity during the first 90 days of storage, but BChE activity noticeably decreased after 90 days.

Conclusions

Serum samples stored in −80 °C for up to 90 days can be exploited to accurately determine BChE activity.

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Butyrylcholinesterase (BChE) activity was measured by a fluorescence turn-on assay.

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BChE activity in human serum was determined during 180-day storage at −80 °C.

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Gender difference on BChE activity was not observed according to t-test.

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Serum BChE activity maintained stability at −80 °C for up to 90 days.

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A clinical criterion on BChE activity measurements is established.

Comparison of two storage methods for the analysis of cholinesterase activities in food animals

Cholinesterases (ChE) are specialized carboxylic ester hydrolases that catalyse the hydrolysis of choline esters. They are classified into either acetylcholinesterase (AChE) or butyrylcholinesterase (BChE). Determination of ChE in the tissues is the appropriate tool for the diagnosis of organophosphorus and carbamate exposures. In general, a significant inhibition was seen in both AChE and BChE activities after 6 months of freezing at −80°C and after 3 months of freezing at −20°C. Linear regression of mean AChE and BChE was observed in all individual samples during the months of the two freezing methods. Bland and Altman plot of the ratios of the two freezing methods have showen the mean difference between the two freezing methods to be 8.8, and SD was 144.7 and −127.6 for upper and lower limits, respectively, for liver, while in muscle the mean difference was 1.5 and SD was 32.5 and −28.9 for upper and lower limits, respectively.

Butyrylcholinesterase activity, cardiovascular risk factors, and mortality in middle-aged and elderly men and women in Jerusalem

BACKGROUND

The association of butyrylcholinesterase (BuChE) with Alzheimer disease and the association of this disease with cardiovascular risk factors raise interest in the association of BuChE activity with cardiovascular risk factors and mortality.

METHODS

A baseline cross-sectional study was conducted between 1985 and 1987, encompassing residents > or =50 years of age living in a Jewish neighborhood in western Jerusalem. Interviews were followed by examinations and nonfasting blood sampling (available for 1807 participants). Follow-up data to April 1996 on mortality and causes of death were obtained through record linkage with the Israeli Population Registry.

RESULTS

BuChE activity was inversely related to age and was positively associated with serum concentrations of albumin (r = 0.35; P <0.001), cholesterol (r = 0.31; P <0.001), and triglycerides (r = 0.30; P <0.001). Enzyme activity was associated with measures of overweight, obesity, and body fat distribution (e.g., body mass index, r = 0.20; P <0.001). In multivariate analysis, the associations of enzyme activity with serum cholesterol, triglycerides, and albumin persisted strongly. After adjustment by Cox proportional hazards regression for other predictors of mortality in this population, individuals in the lowest quintile of BuChE activity had significantly higher mortality than those in the highest quintile [hazard ratios (95% confidence intervals): all-cause mortality, 1.62 (1.15-2.30); cardiovascular deaths, 1.79 (1.05-3.05)]. The association was attenuated by introduction of serum albumin into the models.

CONCLUSIONS

This is the first study to report on the association between BuChE and mortality. The relatively strong association of BuChE with serum lipid and albumin concentrations requires elucidation. Our results suggest that low BuChE activity may be a nonspecific risk factor for mortality in the elderly.

Effects of different variables on whole blood cholinesterase analysis in dogs

The influence of several variables such as sample and reagent storage, anticoagulants, reaction temperature, pH, and substrate concentration on whole blood cholinesterase determination was studied. Storage of nondiluted whole blood samples at room temperature or under refrigeration (4 C) was adequate for short-term storage (3 days to 2 weeks). However, freezing would be more appropriate for long-term storage (> or = 1 month), and successive thawing and freezing did not produce any loss of cholinesterase activity. All reagents (2,2'-dithiodipyridine as chromophore and acetylthiocholine and butyrylthiocholine as substrates) were stable for 3 months when frozen. Heparin and ethylenediaminetetraacetic acid were the most suitable anticoagulants for whole blood acetylcholinesterase and butyrylcholinesterase determination, because citrate yielded lower acetylcholinesterase values and fluoride inhibited butyrylcholinesterase. Increases in reaction temperature and pH yielded higher cholinesterase values but also increased nonenzymatic substrate hydrolysis. Higher cholinesterase and nonenzymatic substrate hydrolysis values were obtained as higher substrate concentrations were used.

Plasma butyrylcholinesterase activity and cocaine half-life differ significantly in rhesus and squirrel monkeys

In vitro studies have implicated butyrylcholinesterase (BChE, E.C.3.1.1.8) as the major enzyme for metabolizing cocaine in humans, but little is known about endogenous BChE activity in monkeys and other animals often used in preclinical studies of cocaine. We compared BChE activity in 18 rhesus and 11 squirrel monkeys, using the colorimetric method of Ellman with butyrylthiocholine as substrate, and in vitro cocaine half-life in pooled plasma samples measuring cocaine concentrations over 60 minutes by GC-MS. Rhesus monkeys had a significantly higher plasma BChE activity than squirrel monkeys (8.2 +/- 0.5 U/L vs. 2.8 +/- 0.5 U/L), and a three-fold shorter in vitro cocaine half-life (20.1 min vs. 60.2 min). BChE activity in rhesus monkeys was comparable to the activity reported in humans. There was no significant influence of age, weight, or prior cocaine exposure. These results indicate that BChE level can vary between species of non-human primates, a factor that should be taken into account when studying drugs such as cocaine which are metabolized by BChE.

Acetylcholinesterase inhibition by zifrosilone: pharmacokinetics and pharmacodynamics

OBJECTIVE

To determine the pharmacokinetics, pharmacodynamics and safety of the acetylcholinesterase inhibitor zifrosilone in healthy male volunteers.

METHODS

Pharmacokinetics, pharmacodynamics, and tolerance of zifrosilone were studied in a double-blind, sequential, single-escalating-dose, randomized panel design. Each panel consisted of six subjects, with four subjects receiving zifrosilone (10, 30, 60, 90, 120, 150, 200, 250, and 300 mg orally) and two subjects receiving matching placebo. Serial blood samples were obtained for zifrosilone plasma concentrations and red blood cell acetylcholinesterase and butyrylcholinesterase activities. Participating subjects (n = 54) were men between the ages of 18 and 45 years. Each subject had a normal physical examination, electrocardiogram, serum chemistries, hematology, urinalysis, and test for human immunodeficiency virus at screening.

RESULTS

A greater than proportionate increase in mean plasma concentration values for area under the curve from time zero to infinity was observed over the 200 to 300 mg dose range groups. Red blood cell acetylcholinesterase showed a dose-inhibition relationship, with a mean maximum inhibition of 20.9% at 10 mg that increased to 62.1% at 300 mg. Butyrylcholinesterase activity was relatively unaffected by zifrosilone (< 20% inhibition at 300 mg). For doses > or = 200 mg, an Emax pharmacodynamic model was used to describe the relationship between zifrosilone plasma concentration and red blood cell acetylcholinesterase inhibition (Emax = 83.8%; EC50 = 0.65 ng/ml).

CONCLUSIONS

Zifrosilone showed dose-dependent pharmacokinetics after oral administration and was effective in causing selective inhibition of red blood cell acetylcholinesterase.

Evaluation of the UV-340 spectrophotometric determination for pseudocholinesterase activity (EC 3.1.1.8) in human serum

A pseudocholinesterase catalytic activity assay using p-hydroxybenzoylcholine as substrate and measuring the decrease of NADPH at 340 nm was compared with a colorimetric method using acetylthiocholine as substrate. The assay is simple, uses 50 microliters serum and is performed at 37 degrees C. Precision of the UV-340 method was good except at low ranges. The catalytic activity was depressed by the anticoagulants citrate and fluoride but not by EDTA or heparin. The reference values obtained with the evaluated UV-340 method are somewhat higher than those with the colorimetric method. As the results with both methods are comparable, the choice of procedure will depend on the local facilities.

The effect of storage at different temperatures on cholinesterase activity in human serum

The effect of storage on the catalytic concentration of cholinesterase and on the reference values of cholinesterase in human serum were studied. When serum was stored at room temperature (20 degrees C), at 4 degrees C and at - 20 degrees C (one year) there was no change in catalytic activity. Even after nine times freezing and thawing (over nine weeks) the catalytic activity was unaffected. The average reference value was significantly higher for males than for females (3.11 +/- 0.57 vs 2.50 +/- 0.43 kU/l).