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PubMed1993

Inhibition of cholinesterases by histamine 2 receptor antagonist drugs.

Many studies have demonstrated that histamine 2 receptor antagonists (H2RA) have in vitro anticholinesterase effects, but discrepancies about type and potency of this inhibitory effect exist among published results. Moreover, cholinesterase inhibition has not been shown in patients receiving H2RA. These discrepancies led us to study the in vitro antibutyryl- and in vitro antiacetylcholinesterase activities of ranitidine, cimetidine, nizatidine comparatively to pyridostigmines. Plasma cholinesterase activity (PCEA), erythrocyte cholinesterase activity (ECEA) and plasma ranitidine levels were measured in six patients before and during continuous IV infusion (150 or 200 mg/d) of ranitidine. Our in vitro results confirm the weak anticholinesterase activity of H2RA. Ranitidine is the most potent inhibitor of butyrylcholinesterase (Ki = 61 microM). Ranitidine and nizatidine are the most potent inhibitors of acetylcholinesterase (Ki' = 2.1 microM, Ki' = 5.1 microM, respectively) but one thousand times less effective than pyridostigmine (Ki = 0.003 microM). The results in patients show no statistically significant difference between PCEA and ECEA measured before and during ranitidine infusion (plasma ranitidine levels between 0.31 and 1.25 microM).

Acetylcholinesterase↗
PubMed1993

Clinical studies on plasma protein C. Correlation with serum cholinesterase.

When compared to 32 healthy normal weight normolipidemic control subjects, plasma protein C antigen and serum cholinesterase activity were significantly decreased in 17 patients with decompensated cirrhosis of the liver and in 29 critically-ill surgical patients displaying the acute phase reaction, most of them without evidence of consumption coagulopathy. The low levels of these variables are considered to be subsequent to impaired and dysregulated hepatic protein synthesis. On the contrary, plasma protein C and serum cholinesterase were increased in 20 nephrotic patients and in 20 overweight hypertriglyceridemic subjects, a finding highly suggestive of enhanced hepatic synthesis probably related to an accelerated turnover of triglycerides. A discrepancy between low serum cholinesterase activity and normal or even high plasma protein C antigen was noted in 15 patients with cholestasis. This was particularly evident in 7 subjects with extrahepatic cholestasis and an abnormal pattern of hepatic protein synthesis or impaired clearance of plasma protein C would appear to develop in such pathological conditions.

Adult↗
PubMedDate not supplied

pH method for determination of cholinesterase in whole blood: collaborative study.

A collaborative study of an indirect method for determination of cholinesterase activity was conducted with cattle blood. Ten collaborators analyzed 8 samples of varying degrees of cholinesterase inhibition. The sample is diluted with a buffer, and the pH change that results from the hydrolysis of acetylcholine is monitored. Repeatability relative standard deviations (RSDr) ranged from 6.6 to 8.6%, and reproducibility relative standard deviations (RSDR) ranged from 10.7 to 17.3% for mean activities of 0.60-0.40 delta pH/h. All samples that were completely inhibited were detected. The method was adopted first action by AOAC International for determination of cholinesterase activity in whole bovine blood.

Acetylcholine↗
PubMed1993

A cholinesterase testing program for pesticide applicators.

Illnesses associated with the increased use of cholinesterase-inhibiting pesticides have brought about recommendations for monitoring pesticide applicators. The State of California requires medical supervision; however, the supervision and monitoring guidelines are often incorrectly followed. In this retrospective cohort study, 103 worker-years of cholinesterase monitoring are reported. Twenty-four (24%) workers were temporarily removed from spraying (five were removed twice) because their cholinesterase plasma activity levels were below 60% of baseline. Five workers (5%) had mild symptoms of toxicity but none reported a specific incident of exposure. Hispanic workers had fewer significant drops in plasma activity levels and fewer toxic symptoms than white workers. The relative risk of pesticide poisoning was increased in workers whose initial baseline plasma levels were low or if their levels had already dropped to 60%-80% of their baseline previously in the season. Case studies and differences in baselines by month of determination suggest poor monitoring compliance by the companies and employees. Suggestions of how the physician can overcome these problems and improvements of the guidelines are discussed.

Adolescent↗
PubMed1993

Cholinesterase response in the rhabdomyosarcoma tumor and small intestine of the BALB/c mice and the radioprotective actions of exogenous ATP after lethal dose of neutron radiation.

The rhabdomyosarcoma tumors were subjected to different doses of 2.0, 3.8 and 7.0 Gy from a neutron beam facility p(66 MeV)/Be. Elevated levels of cholinesterase activity are observed in which there is a correlation between the different doses of neutron radiation and the augmentation response of this enzyme. The increase of cholinesterase activity after 7 Gy neutron irradiation as a feature of involvement in the homeostatic mechanism maintaining the proper choline/acetylcholine ratio in the cell is also observed at 1 and 24 h in both tissues, rhabdomyosarcoma and small intestine. The activity of the enzyme after neutron irradiation with prior administration of ATP showed smaller increases when compared with increases observed after neutron irradiation alone. Moreover in the present work the protective mechanism of ATP in the response of cholinesterase activity is marked differential between both, normal and tumoral tissue and correlated inversely with the administered of the following concentrations of exogenous ATP (8, 25, 80, 250, and 700 mg/kg body weight) prior to exposure to 7 Gy neutron radiation. These results reflect the radioprotective ability of exogenous ATP to exert a number of metabolic adaptations as a defense mechanism in which the cell exposed to neutron radiation could remain viable because the injury is potentially repairable.

Adenosine Triphosphate↗
PubMed1996

Distribution of cholinesterase activity in the population of Trinidad.

The relation between the level or the quality of serum cholinesterase and susceptibility to succinylcholine-induced apnea is significant because the abnormality resides in a low affinity variant rather than in a quantitative deficiency. A population study was undertaken in Trinidad to determine the pattern of the cholinesterase phenotype, using quantitative biochemical tests and the dibucaine number. Of 1290 subjects, 567 were African, 418 were Indian, 237 were of mixed lineage, and 68 belonged to the minority races. The dibucaine number did not differ between races or sexes. Of the population, 98.5% had normal enzyme characteristics. Indians had the highest values for the dibucaine number and the enzyme activity. Cholinesterase was significantly higher in African and mixed males. The homozygous atypical gene was not detected, but the frequency of the heterozygous "atypical" variant was highest in the minority races and lowest in Africans. Two sisters of Indian descent demonstrated the presence of the silent gene.

Adolescent↗
PubMedDate not supplied

[The interaction of hexamethonium derivatives with the cholinesterases of vertebrates and invertebrates. The physicochemical and conformational aspects].

Conformational and geometrical properties of the hexamethylenebis(trimethylammonium) (CH3)3N+-(CH2)6)-N+(CH3)3 (hexamethonium) and its derivatives with various degree of conformational flexibility of interonion chain having disulfide or two dimethylsilane groups or difluoromethylene chain instead of cholinesterase reversible inhibitors have been determined using molecular mechanics methods. Conformation-activity relationships between these inhibitors and different cholinesterases (human erythrocyte acetylcholinesterase, horse plasma butyrylcholinesterase, cholinesterase from the brain of the grass frog Rana temporaria and optical ganglia from the Pacific squid Todarodes pacificus and Comandor squids Berryteuthis magister from various areas) were investigated. Hypothesis of complex influence of conformational and geometrical properties (if molecules on anticholinesterase efficiency of compounds under investigation was formulated.

Animals↗
PubMed1977

Calorimetry of cholinesterase activity in serum.

Cholinesterase activity in human serum was measured calorimetrically and compared to values obtained with the spectrophotometric method of Rappaport et al. [Clin. Chim. Acta 4, 227 (1959)]. The response of the calorimeter upon mixing serum with acetylcholine corresponded to the cholinesterase activity of the serum, the thermogram peak height being linearly related to enzyme activity at serum dilution volumes at which interference heat was negligible. The interference heat contributed by the dilution mixing characteristics of serum, studied separately, was found to be similar for heat-denatured, aged, or lyophilized samples. In all cases, heat of mixing was negligible when 1 ml of serum in buffer (2/3 by vol) was mixed with 1 ml of buffer. When this amount of serum was assayed with acetylcholine, cholinesterase activities of 2 and 3 kU/liter were recorded as thermograms with peak heights of 2.3 and 3.5 cm, respectively.

Acetylcholine↗
PubMed1994

Blood cholinesterase levels in a group of Malaysian blood donors.

Data on blood cholinesterase levels in the Malaysian population is lacking. The spectrophotometric method of Ellman was used to determine the red cell, plasma and whole blood cholinesterase (ChE) levels in 407 Malaysian blood donors. The mean+1SD for plasma ChE in females (n = 48) was 2.37 + 0.70 umol/min/ml and 2.76 + 0.75 umol/min/ml in males (n = 359). The mean plasma ChE in males was higher than in females (p < 0.001). The mean+1SD for red cell ChE in females was 9.01 + 1.20 umol/min/ml whereas in males it was 7.69 +1.30 umol/min/ml (the mean red cell ChE in females was higher than in males, p < 0.0001). The mean+1SD for whole blood ChE for females was 4.31+ 0.58 umol/min/ml and for males it was 4.95 + 0.71 umol/min/ml. The mean whole blood ChE in males was higher than in females (p < 0.0001). Sex influenced the plasma, red cell and whole blood ChE. In males the plasma ChE was affected by the race factor. The mean+1SD plasma ChE for the Malay, Chinese and Indian were 2.92 + 0.80, 2.73 + 0.71 and 2.61+ 0.73 respectively (p < 0.002). The age factor in males affected the red cell ChE with 7.88 + 1.32 in the (30-69) age group and 7.47 + 1.23 in the (15-29) age group (p < 0.005). The whole blood ChE in females was affected by blood groups. The mean+1SD whole blood ChE for blood groups A,B and O were 4.19 + 0.42, 3.93 + 0.46 and 4.49 + 0.62 respectively (p < 0.03). The significant difference is between the ChE of group B and O, but the ChE of group A could not be determined to be different from group B or O. These results serve as guidelines for our local population in the evaluation of cholinesterase levels with regard to pesticide poisoning, liver biosynthetic capacity and unusual sensitivity to succinylcholine.

Adolescent↗
PubMed1997

[The diagnostic usefulness of cholinesterase in pleural exudates].

BACKGROUND AND OBJECTIVES: The pleural fluid/serum cholinesterase ratio (PF/S) is the most efficient parameter to differentiate transudates from exudates. The objective of this study was to evaluate whether its determination might yield additional diagnostic information in pleural exudates. MATERIALS AND METHODS: A total of 167 patients with the diagnosis of pleural exudate were studied: 74 carcinomatous, 32 tuberculous, 31 parapneumonic, 30 other causes. Pleural fluids were divided on the basis of lymphocyte or polymorphonuclear predominance and were grouped according to diagnosis. The PF/S cholinesterase ratio was determined in all patient. RESULTS: In lymphocytic exudates, when PF/S ratio was < 0.42 pleural effusion was classified as malignant, with a sensitivity (S) of 56% (95% CI: 43%-66%) and a specificity (SP) of 90% (95% CI: 78%-95%). For the diagnosis of tuberculosis, in the total of pleural effusions, a ratio > or = 0.45 showed a S of 97% (95% CI: 82%-99%) and a SP of 51% (95% CI: 42%-59%). CONCLUSIONS: The PF/S cholinesterase ratio yielded an useful information on the diagnosis of pleural exudates. Thus, in our series of patients, a ratio < 0.42 in a lymphocytic effusion suggested a malignant origin, and a ratio < 0.45 practically ruled out tuberculosis, irrespective of the cellular predominance in the pleural fluid.

Adult↗
PubMedDate not supplied

Pharmacokinetics and drug interactions of cholinesterase inhibitors administered in Alzheimer's disease.

Cholinesterase inhibitors are the first agents to be successfully developed specifically for the treatment of cognitive decline associated with Alzheimer's disease. Basic knowledge of their pharmacokinetics is important to their appropriate administration. Their pharmacokinetics help determine the magnitude and duration of their pharmacologic effects, and also the manner in which they affect the degree of cholinesterase inhibition and recovery. The clinical utility of measuring these values in daily practice awaits further research. Drug interactions with cholinesterase inhibitors may occur by pharmacokinetic or pharmacodynamic mechanisms. For the most part, interactions that are mediated by the hepatic cytochrome P-450 system have been inadequately evaluated.

Alzheimer Disease↗
PubMed1993

Cholinesterase reactivation in organophosphorus poisoned patients depends on the plasma concentrations of the oxime pralidoxime methylsulphate and of the organophosphate.

We measured in nine patients, poisoned by organophosphorus agents (ethyl parathion, ethyl and methyl parathion, dimethoate, or bromophos), erythrocyte and serum cholinesterase activities, and plasma concentrations of the organophosphorus agent. These patients were treated with pralidoxime methylsulphate (Contrathion), administered as a bolus injection of 4.42 mg.kg-1 followed by a continuous infusion of 2.14 mg.kg-1/h, a dose regimen calculated to obtain the presumed "therapeutic" plasma level of 4 mg.l-1, or by a multiple of this infusion rate. Oxime plasma concentrations were also measured. The organophosphorus agent was still detectable in some patients after several days or weeks. In the patients with ethyl and methyl several days or weeks. In the patients with ethyl and methyl parathion poisoning, enzyme reactivation could be obtained in some at oxime concentrations as low as 2.88 mg.l-1; in others, however, oxime concentrations as high as 14.6 mg.l-1 remained without effect. The therapeutic effect of the oxime seemed to depend on the plasma concentrations of ethyl and methyl parathion, enzyme reactivation being absent as long as these concentrations remained above 30 micrograms.l-1. The bromophos poisoning was rather mild, cholinesterases were moderately inhibited and increased under oxime therapy. The omethoate inhibited enzyme could not be reactivated.

Adult↗
PubMed1995

Evaluation of the decarbamylation process of cholinesterase during assay of enzyme activity.

The activity of carbamylated cholinesterase increases continuously during assay, suggesting that progressive decarbamylation takes place. The following effects of assay conditions on the observed decarbamylation were studied: the effect of the sulfhydryl group of nitrobenzoate produced in the course of Ellman assay, the effect of substrate and the effect of sample dilution during assay. This study indicates that sample dilution is the main trigger to the decarbamylation observed during assay of cholinesterase activity. The process was described as a first-order reaction during which the inhibited enzyme gives place to the active form. Kinetic constants for decarbamylation of human pseudocholinesterase (EC 3.1.1.8) at 30 degrees C were approximately 0.005 min-1 for dimethylcarbamates and 0.010 min-1 for monomethylcarbamates, when 1 mmol/l propionylthiocholine was used as substrate.

Aldicarb↗
PubMed1964

A RADIOMETRIC METHOD FOR ESTIMATING BLOOD CHOLINESTERASE IN THE FIELD.

A radiometric method has been developed which provides for the simple and rapid measurement of human blood cholinesterase under field conditions. The method involves minimal dilution of samples and the use of very low substrate concentrations, and is therefore more sensitive to cholinesterase inhibition by reversible anticholinesterases such as carbamates than the conventional manometric or DeltapH methods. A 20-mul sample of haemolysed whole blood is mixed with (14)C-labelled acetylcholine on a cavity microscope slide. After half a minute or three minutes the mixture is acidified and dried. Under these conditions radioactive acetate liberated enzymically is completely volatile while the radioactive unhydrolysed substrate is not. The loss of radioactivity on acidification and drying is therefore a direct measure of the acetylcholinesterase activity. The levels of radioactivity employed are far below those likely to present any significant health hazard or to require special laboratory conditions. Although the method requires a labelled substrate, a single preparation is sufficient for several hundred thousand enzyme assays. The method has been tested under simulated field conditions.

Acetylcholine↗
PubMed1988

Feline islands of Calleja complex: II. Cholinergic and cholinesterasic features.

Histochemical analyses demonstrated that the islands of Calleja complex (ICC) in the cat is exceptionally rich in choline acetyltransferase (ChAT) and acetylcholinesterase (AChE). Both enzymes are found in neuropil throughout the complex, as well as in a subset of the satellite neurons accompanying Callejal islands. Lateromedial changes in these cholinergic and cholinesterasic tissue elements were consistent with our previous finding that the feline ICC is cytoarchitecturally divided into five successively more medial types of island-satellite cell ensembles or units. In particular, satellite neurons reactive for ChAT and AChE diminished progressively in size and increased steadily in number from the most lateral to the most medial units. A concomitant increase in neuropil levels of both enzymes suggested that the strong cholinergic innervation of the feline ICC is at least partially derived from satellite cells. This possibility gained further credibility from the additional observation that very fine processes from some ChAT and AChE satellite neurons projected into the terminal-like cholinergic field permeating the granular Callejal islands. The granule cells themselves lacked ChAT and (apart from potentially artifactual cases) AChE, as did adjoining groups of dwarf cells and small pyramidal like neurons. The cholinergic and cholinesterasic satellite neurons were preferentially located above tubercular Callejal islands and in otherwise cell-poor spaces within the isla magna. Such neurons appeared to be isodendritic: they commonly had ovoidal somata with one or two processes lacking enzyme-reactive spines. Depending on the type of ICC unit involved, their mean soma length ranged from 15 to 24 micron, all but the largest of which was distinctly smaller than that of ChAT and AChE cells in striatal or basal nuclear structures. Not all the cholinesterase neurons in the feline ICC are cholinergic, judging from the finding that there are a significantly greater number of satellite neurons containing AChE than ChAT. Three cholinergic features of the feline ICC are especially noteworthy. First, each of the island-satellite cell ensembles in the complex is unified by AChE neuropil often denser than that of adjacent striatal areas. Second, cholinergic neuropil is exceptionally dense in the isla magna and in a subpial band under medial Callejal islands. Third, ChAT neurons in the isla magna are among the smallest cholinergic cells found in the brain.

Acetylcholinesterase↗
PubMed2006

Homocysteine thiolactone and human cholinesterases.

1. The cholinergic system is important in cognition and behavior as well as in the function of the cerebral vasculature. 2. Hyperhomocysteinemia is a risk factor for development of both dementia and cerebrovascular disease. 3. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are serine hydrolase enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine, a key process in the regulation of the cholinergic system. 4. It has been hypothesized that the deleterious effects of elevated homocysteine may, in part, be due to its actions on cholinesterases. 5. To further test this hypothesis, homocysteine and a number of its metabolites and analogues were examined for effects on the activity of human cholinesterases. 6. Homocysteine itself did not have any measurable effect on the activity of these enzymes. 7. Homocysteine thiolactone, the cyclic metabolite of homocysteine, slowly and irreversibly inhibited the activity of human AChE. 8. Conversely, this metabolite and some of its analogues significantly enhanced the activity of human BuChE. 9. Structure-activity studies indicated that the unprotonated amino group of homocysteine thiolactone and related compounds represents the essential feature for activation of BuChE, whereas the thioester linkage appears to be responsible for the slow AChE inactivation. 10. It is concluded that hyperhomocysteinemia may exert its adverse effects, in part, through the metabolite of homocysteine, homocysteine thiolactone, which is capable of altering the activity of human cholinesterases, the most pronounced effect being BuChE activation.

Acetylcholinesterase↗
PubMed1990

Quantitative analyses of plasma cholinesterase isozymes in haloperidol-treated rats.

We describe a quantitative slab gel electrophoresis procedure that allows quantitative determination of plasma levels of discrete cholinesterase isozymes. Using this method, the effects of haloperidol treatment on plasma cholinesterase isozyme levels were examined in normal rats. Eight isozymes were detected by enzymatic reaction with either of two substrates (alpha-naphthyl acetate, NA; acetylthiocholine iodide, AcTCh), and then quantified using densitometric scanning. With AcTCh substrate, the activities of two major isozymes (1 and 2) were found to be linear with increasing quantities of applied plasma. With NA as substrate, Iso-OMPA (a pseudocholinesterase inhibitor) inhibited activities of all isozymes, except isozymes 2 and 8. With either substrate, BW284C51 (acetylcholinesterase inhibitor) inhibited 100% and 13% of activity of isozymes 2 and 8, respectively, and with AcTCh substrate, 37% of isozyme 1. Based on the differential patterns of substrate specificity and action of inhibitors, and the reproducibility of patterns, we propose that these isozymes represent distinct molecular species. Short-term (14 days) and long-term (45 days) haloperidol treatment both resulted in altered levels of specific cholinesterase (ChE) isozymes. On the average, with AcTCh substrate, haloperidol treatment increased levels of isozymes 1 and 2 by 30% and 8%, respectively, after 14 days, and by 50% and 30%, respectively, after 45 days. Isozymes 3 through 8 showed minor changes. Plasma levels of isozymes 1 and 2 returned to baseline pretreatment values after a 40-day drug-free period. No significant change was observed after either short- or long-term treatment with clozapine, imipramine, or saline, or after an acute (less than 5 days) haloperidol treatment. No change was noted in RBC-ChE levels as function of treatment. These findings indicate that, in the rat, chronic haloperidol treatment results in differential changes in the plasma levels of discrete ChE isozymes. We have suggested that these changes reflect an alteration of central dopaminergic-cholinergic balance.

Acetylcholinesterase↗
PubMed1984

Localization of cholinesterase activity in the outer plexiform layer of the larval tiger salamander retina.

Acetylcholinesterase activity, which may be indicative of cholinergic synapses, has been ultrastructurally localized in the outer plexiform layer of the larval tiger salamander retina using the cholinesterase staining method of Karnovsky and Roots. In the presence of the butyrylcholinesterase inhibitor, ethopropazine, precipitate is localized to discrete 'stain laminae' about 300 nm in their largest dimension and bounded by a 10 nm wide electron-lucent gap. Stain laminae are predominantly found adjacent to horizontal cell axon terminals which were identified by serial section analysis. Stain precipitate has not been found associated with horizontal cell dendrites and in only one case was a lamina found adjacent to a bipolar cell dendrite. Intracellular deposits of cholinesterase stain precipitate were also observed. In some cases, stain is found adjacent to synaptic ribbons in photoreceptor terminals. Likely artifacts appear to have been ruled out by control experiments in which retinas either were not treated with cholinesterase stain or were treated in the presence of the specific acetylcholinesterase inhibitor, BW284C51. Thus, the stain laminae probably result from specific, highly localized areas of acetylcholinesterase activity. The implications of the present study on current theories of cholinergic function in the vertebrate retina are discussed.

Acetylcholinesterase↗