Rate assay for determination of serum pseudo-cholinesterase activity

Preliminary evidence that rivastigmine-induced inhibition of serum butyrylcholinesterase activity improves behavioral symptoms in Japanese patients with Alzheimer's disease

AIM

To investigate whether the inhibitory rate of serum butyrylcholinesterase (BuChE) activity in Japanese patients with Alzheimer's disease is correlated with cognitive function, behavioral symptoms and caregiver burden.

METHODS

A total of 61 patients with mild to moderately severe Alzheimer's disease who were not undergoing cholinesterase enzyme inhibitor/memantine combinatorial treatment received a rivastigmine (18 mg) patch for 24 weeks. The rate of inhibition of BuChE was correlated with scores obtained on cognitive (Mini-Mental State Examination), behavioral (the Japanese version of the modified Crichton Geriatric Behavioral Rating Scale [CGBRS] and Vitality Index [VI]) and burden (the Japanese version of Zarit Burden Inventory [ZBI]) scales; and the Clinical Global Impression of Change scale.

RESULTS

The serum BuChE activity showed a significant decrease after 24 weeks compared with baseline (P < 0.001). Overall, significant effects were found in the Mini-Mental State Examination score, VI score and modified CGBRS score. We then divided patient groups into a high inhibitory rate (≥40%) group and a low inhibitory rate (<40%) group; there were significant improvements in the Mini-Mental State Examination score, VI score and modified CGBRS score in both groups. However, favorable results were seen in cooperation, restlessness and leisure on modified CGBRS subscales in the high inhibitory rate group (P < 0.001, P = 0.007, P < 0.001, respectively), and rehabilitation and other activities on VI subscales in the high inhibitory rate group (P = 0.005) compared with those in the low inhibitory rate group.

CONCLUSIONS

Demonstrable significant improvements in behavioral symptoms, such as low cooperation, restlessness or low activities in patients with Alzheimer's disease, were achieved on inhibition of BuChE at a rate of 40% or more. Geriatr Gerontol Int 2017; 17: 1306-1312.

Conserved and non-conserved residues and their role in the structure and function of p-hydroxybenzoate hydroxylase

In order to elucidate the molecular mechanism of the catalytic reaction and enzyme conformation, we substituted 53 conserved residues identified by aligning 92 p-hydroxybenzoate hydroxylase sequences and 19 non-conserved residues selected from crystallographic studies of Pseudomonas fluorescens NBRC14160 p-hydroxybenzoate hydroxylase with 19 other naturally occurring amino acids, yielding a database of 619 active single mutants. The database contained 365 and 254 active single mutants for 44/53 conserved residues and 19 non-conserved residues, respectively; the data included main activity, sub-activity for NADPH and NADPH reaction specificity. Active mutations were not observed for the G14, Q102, G160, E198, R220, R246, N300, F342 and G387 conserved residues, and only one active mutant was obtained at the G9, G11, G187, D286, Y201, R214 and G295 conserved residues and the S13, E32 and R42 non-conserved residues. Only seven active mutants with higher activity than the wild-type enzyme were observed at conserved residues, and only two were observed at non-conserved residues. The 365 mutants at conserved residues included 64 active mutants with higher NADPH reaction specificity than the wild-type enzyme, and some Y181X single mutants exhibited considerable changes in NADPH reaction specificity. A Y181X/L268G double-mutant database was constructed to computationally analyze the effects of these substitutions on structural conformation and function. These results indicated that some conserved or non-conserved residues are important for structural stability or enzyme function.

Serum aspirin esterase activity is lower in end-stage renal disease patients than in healthy control subjects and increases after haemodialysis

Background

Studies regarding aspirin metabolism can be important in patients with renal failure who have an increased risk of cardiovascular diseases. We undertook this study to assess the aspirin esterase (AE) status in end-stage renal disease (ESRD) patients.

Methods

A total of 42 patients on long-term haemodialysis (HD) with a mean dialysis course of 6.1 y were recruited.

Results

Serum AE levels were 44% lower and cholinesterase (ChE) levels were 22% lower in ESRD patients before dialysis as compared with control subjects ( P = 0.0001). A very strong correlation was found between AE and ChE levels. AE levels increased on average 28% after dialysis with adjustments for age, gender, total cholesterol, triglyceride and high-density lipoprotein cholesterol ( P = 0.002). In addition, ChE levels were significantly increased (48%) after dialysis ( P = 0.0001). Changes in AE activity were significantly and positively correlated with those of ChE ( r = 0.427, P = 0.005). When we adjusted for several confounders, we found that the changes in AE activity operated by dialysis are significant independently of age, gender, aspirin (ASA) intake, cholesterol, triglycerides, high-density lipoprotein cholesterol and ChE.

Conclusions

We report that serum AE activity is significantly lower in ESRD and that treatment by HD results in an increase of activity. We confirm that AE is associated with lipid parameters and ChE. Our results show variations in ASA catabolism between the dialysis sessions, suggesting an oscillating pattern in ASA disposal in these patients. The mechanisms for reduced AE activity in uraemia and the effects of HD need further investigation.

Serum aspirin esterase is strongly associated with glucose and lipids in healthy subjects: different association patterns in subjects with type 2 diabetes mellitus

BACKGROUND

Aspirin esterase (AE) activity can account for part of aspirin pharmacokinetics in the circulation, possibly being associated with the impairment of aspirin effectiveness as an inhibitor of platelet aggregation.

AIMS

The study was aimed at investigating the correlations of serum AE activity with cholinesterase (ChE) and metabolic variables in healthy subjects in comparison to subjects with type 2 diabetes mellitus (T2DM).

METHODS

In cardiovascular disease-free T2DM subjects and healthy controls, the AE activity levels and/or the correlation patterns between AE and the other variables were analyzed.

RESULTS

Neither AE nor ChE activities were higher in the subjects with T2DM. Serum AE activity strongly correlated with ChE as well as glucose/lipids variables such as total cholesterol and triglyceride in healthy subjects, while the correlations between AE and glucose/lipids variables were not present in T2DM subjects.

CONCLUSIONS

These data may reflect the pathophysiological changes between healthy and T2DM subjects. Our data may thus provide the basis for future studies to unravel the mechanisms.

A Systematic and Comprehensive Combinatorial Approach to Simultaneously Improve the Activity, Reaction Specificity, and Thermal Stability of p-Hydroxybenzoate Hydroxylase

We have simultaneously improved the activity, reaction specificity, and thermal stability of p-hydroxybenzoate hydroxylase by means of systematic and comprehensive combinatorial mutagenesis starting from available single mutations. Introduction of random mutations at the positions of four cysteine and eight methionine residues provided 216 single mutants as stably expressed forms in Escherichia coli host cells. Four characteristics, hydroxylase activity toward p-hydroxybenzoate (main activity), protocatechuate-dependent NADPH oxidase activity (sub-activity), ratio of sub-activity to main activity (reaction specificity), and thermal stability, of the purified mutants were determined. To improve the above characteristics for diagnostic use of the enzyme, 11 single mutations (C152V, C211I, C332A, M52V, M52Q, M110L, M110I, M213G, M213L, M276Q, and M349A) were selected for further combinatorial mutagenesis. All possible combinations of the mutations provided 18 variants with double mutations and further combinatorial mutagenesis provided 6 variants with triple mutations and 9 variants with quadruple mutations with the simultaneously improved four properties.

Lipid peroxidation is enhanced in Yusho victims 35 years after accidental poisoning with polychlorinated biphenyls in Nagasaki, Japan

Thirty-five years have passed since the accidental poisoning with polychlorinated biphenyls (PCB) in Japan and yet high concentrations of PCB are still detected in the serum of the victims. PCB produces superoxide and thus victims are considered to be in a persistent state of oxidative stress. Urinary concentrations of 8-isoprostane (8IP) in the victims and age-matched controls were measured to assess this hypothesis. The mean urinary concentration of 8IP was significantly higher than that in the controls. There was a positive correlation between urinary 8IP and serum concentrations of cholinesterase. It was considered that Yusho is an oxidative stress and 8IP is a useful tool for checking the oxidative condition in Yusho victims.

Radiolabeled cholinesterase substrates: in vitro methods for determining structure-activity relationships and identification of a positron emission tomography radiopharmaceutical for in vivo measurement of butyrylcholinesterase activity

There is currently great interest in developing radiolabeled substrates for acetylcholinesterase and butyrylcholinesterase that would be useful in the in vivo imaging of patients with Alzheimer's disease. Using a simple in vitro spectrophotometric assay for determination of enzymatic cleavage rates, the structure-activity relationship for a short series of 1-methyl-4-piperidinyl esters was investigated. Relative enzymatic hydrolysis rates for the well-characterized 1-methyl-4-piperidinyl acetate, propionate, and i-butyrate esters were in agreement with literature values. The 4 and 5 carbon esters of 1-methyl-4-piperidinol were specific for butyrylcholinesterase and cleaved in the rank order n-valerate > n-butyrate >> 2-methylbutyrate, iso-valerate. These spectrophotometric results were also in agreement with in vitro hydrolysis rates in mouse blood and with in vivo regional retention of radioactivity in mouse brain of 11C-labeled analogs. Brain uptake and apparent enzymatic rate constants for 1-[11C]methyl-4-piperidinyl n-butyrate and n-valerate were calculated from in vivo measurements in M. nemistrina using positron emission tomography. Based on higher brain uptake of radioactivity and superior pharmacokinetics, 1-[11C]methyl-4-piperidinyl n-butyrate was identified as a new radiopharmaceutical for the in vivo measurement of butyrylcholinesterase activity.

Acetylcholine determination of cerebrospinal fluid in aneurysmal subarachnoid hemorrhage

Acetylcholine (ACh) concentrations were determined serially in cerebrospinal fluid (CSF) obtained from 23 patients with aneurysmal subarachnoid hemorrhage (SAH) by high-performance liquid chromatography (HPLC) with electrochemical detection (ED). The values of CSF ACh were significantly low in the initial stage of SAH, and increased subsequently but they did not return to control values within 3 weeks. In addition, serial measurements of CSF butyrylcholinesterase (BChE) activity in 12 SAH patients showed that the activity was elevated significantly in the initial stage of SAH and returned to control levels within a week. This discrepancy in the recovery period between the ACh levels and the BChE activity in CSF indicated that significantly lower CSF ACh levels after SAH could not be attributed to plasma BChE contamination of CSF. These results suggested central cholinergic dysfunction after SAH, especially in the initial stage.

Enzyme-linked immunosorbent assay for serum pseudocholinesterase

We developed a reliable enzyme-linked immunosorbent assay using purified pseudocholinesterase (ChE) as a standard and its monoclonal antibody. The precision, reproducibility, and sensitivity of this assay were quite satisfactory. Serum ChE concentration in 506 normal individuals ranging from 20 to 60 years of age was 3.78 +/- 0.32 mg/l (mean +/- 1 S.D.), though age- and sex-related differences were present. Measurements of ChE concentration and ChE enzymatic activity by two different assay kits in 63 serum samples taken in the Clinical Laboratory of the Jichi Medical School correlated closely. Quantitative determination of serum ChE concentration can be clinically useful: it is much easier and requires far less restricting conditions than does determination of ChE enzymatic activity. Also, it can be performed quite easily under far less demanding conditions. Further, the method is easy to standardize, and this standardization may be applied when the assay is used to evaluate ChE enzymatic activity.

Mechanized assay of serum cholinesterase by specific colorimetric detection of released acid

An automated assay method has been developed for the measurement of serum cholinesterase activity. The samples were prepared by an automated liquid handling unit and incubated for 9.7 min at 30 degrees C, followed by automatic injection into a colorimetric flow injection determination system for acetic acid liberated from acetylcholine by cholinesterase catalytic activity. The coloration reaction employed is based upon the formation of 2-nitrophenylhydrazide utilizing a water-soluble carbodiimide and has a high selectivity for carboxylic acids. The coefficients of variation of the proposed method were 2.4% for within-run analysis (n = 14) and 2.6% for between-run analysis (n = 6). Sera of 55 hospitalized patients were analyzed and the values obtained correlated well with an automated differential pH method (gamma = 0.989).

Estimation of cholinesterase activity (EC 3.1.1.7; 3.1.1.8) in undiluted plasma and erythrocytes as a tool for measuring in vivo effects of reversible inhibitors

In vivo effects of reversible inhibitors of cholinesterase activity were determined radiometrically in undiluted samples of erythrocytes and plasma. [14C]acetylcholine at substrate saturation, 25 degrees C and pH 7.4 permitted rapid and precise determination of butyrylcholinesterase (EC 3.1.1.8) and acetylcholinesterase (EC 3.1.1.7) activities. Reference values for acetylcholinesterase and butyrylcholinesterase were estimated in the plasma and erythrocyte haemolysate of 102 healthy volunteers. The time course of in vitro inhibition was monitored, starting immediately after addition of 9-amino-1,2,3,4-tetrahydroacridine (tacrine), eserine or pyridostigmine to undiluted human plasma. Maximal inhibition (in vitro) was seen within 60 min with tacrine and eserine, in contrast to 180 min with pyridostigmine. The inhibition remained constant for more than 10 h except with eserine, from which enzyme activity showed an early recovery. Concentration response experiments were performed in undiluted human plasma and undiluted human erythrocyte haemolysate. Ki-values of tacrine, eserine and pyridostigmine were estimated. In contrast to pyridostigmine and eserine, tacrine was found to have a higher affinity for butyrylcholinesterase than for acetylcholinesterase. Tacrine at 2.5 mumol/l resulted in complete inhibition of butyrylcholinesterase and 70% inhibition of acetylcholinesterase activity. Dilution of these samples up to 100-fold was accompanied by almost complete recovery of acetylcholinesterase and by 50% recovery of butyrylcholinesterase.

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.

A micro-method for the detection of butyrylcholinesterase secreted by hepatocytes in vitro

A new assay has been developed for detection of butyrylcholinesterase (EC 3.1.1.8) activity based upon the change in absorbance of phenol red, caused by the release of butyric acid from the substrate. Using commercially available enzyme prepared from horse serum, linear, dose-related decreases in absorbance were obtained, generally with correlation values of 0.965 or greater. The assay was modified and used to detect enzyme activity in the supernatants from primary cultures of mouse hepatocytes. The enzyme-mediated response was inhibited by NN'-diisopropylphosphorodiamidic anhydride, a specific inhibitor of butyrylcholinesterase.