Measurement of erythrocyte acetylcholinesterase and plasma cholinesterase activity by a differential pH technique

Relationship Between Pesticide Exposure Factors and Health Symptoms Among Chili Farmers in Northeast Thailand

OBJECTIVES

The unsafe use of pesticides in agriculture represents a major hazard to human health. This study was conducted to investigate the association between pesticide exposure and health symptoms among chili farmers in northeast Thailand.

METHODS

This cross-sectional analytic study included 141 chili farmers in Sakon Nakhon Province, in northeast Thailand. Data regarding health symptoms were gathered using a self-report questionnaire. A medical technician tested blood cholinesterase activity using an erythrocyte method, and an occupational medicine specialist at Ramathibodi Hospital in Bangkok, Thailand reviewed the results. Associations between personal characteristics, pesticide exposure factors, and health symptoms were analyzed using multiple logistic regression.

RESULTS

Of the 141 chili farmers studied, 66.7% experienced pesticide poisoning, as indicated by below-normal cholinesterase levels. Fatigue was the most frequently reported symptom associated with pesticide exposure, affecting 37.6% of participants. This was followed by nausea and vomiting (31.9%), dizziness (14.9%), and dry throat (14.9%). Multivariate logistic regression analysis revealed that several factors were significantly associated with adverse symptoms: amount of work experience, volume of pesticides used, use of chemical pesticides, use of leaking containers during spraying, direct pesticide exposure while working, contact with pesticide-soaked clothing, consumption of food and drinks in the fields, and blood cholinesterase level indicating risk.

CONCLUSIONS

This study suggests potential health risks for chili farmers stemming from exposure to and contamination by pesticides used in agricultural practices. To mitigate these risks, it is essential to supply personal protective equipment and to implement educational programs aimed at improving protective behaviors among farmers.

RBC cholinesterase inhibition: a useful surrogate marker for cholinesterase inhibitor activity in Alzheimer disease therapy?

Red blood cell (RBC) acetylcholinesterase (AChE) inhibition has been used as a peripheral surrogate marker for the activity of centrally acting AChE inhibitors (AChEIs) in the treatment of Alzheimer disease. As a valid peripheral surrogate marker, RBC AChE inhibition should reflect the central pharmacodynamic activity of the compound and should demonstrate a relation with cognitive or global improvement in patients with Alzheimer disease. As a useful clinical tool, RBC AChE inhibition should also provide an advantage in dose optimization. However, the application of surrogate markers in research and clinical use is controversial (Prentice, 1989; Gotzsche, 1996; Colburn, 1997; De Gruttola et al., 1997). For instance, surrogate markers that have been identified or applied inappropriately can lead to erroneous conclusions, slowing the drug development process (Colburn, 1997). Also, the validation of surrogate markers for the pharmacodynamic activity of central nervous system drugs is not always possible because samples of brain tissue cannot be analyzed in humans. Finally, although validation of peripheral markers for central nervous system drugs has been approached via analysis of cerebrospinal fluid (Cutler et al., 1998a), few markers have been subjected to such rigorous evaluation in clinical studies. The extent to which measures of peripheral AChE inhibition accurately model central drug activity and therapeutic effectiveness of AChEIs, both as individual agents and as a drug class, is the focus of this review. AChEIs comprise a group of structurally diverse compounds with a wide range of relative specificities for the various molecular species of cholinesterase found in plasma, RBCs, and the brain. Studies of RBC AChE inhibition after administration of AChEIs in animals are of limited utility because of the differential sensitivity of AChEIs for human versus animal forms of AChE, the poor correlation between effective doses in animals and humans, and the lack of standardized measurements of effectiveness. Although clinical studies of donepezil, metrifonate, and eptastigmine have suggested the potential use of RBC AChE inhibition as a predictor of clinical response, the degree of inhibition yielding maximum cognitive improvements was highly variable from compound to compound (30-80%). Further, investigators did not prove a relation between central and peripheral pharmacodynamics or demonstrate an advantage over dose in the ability of RBC AChE inhibition to predict clinical response. A study of rivastigmine in patients with Alzheimer disease revealed that cerebrospinal fluid AChE inhibition correlated well with cognitive performance, whereas peripheral inhibition did not. Therefore, RBC cholinesterase inhibition is not a reliable surrogate marker for the activity of AChEIs as a class of drugs, and its usefulness as a dose optimization tool for individual agents has yet to be demonstrated clearly.

Long-lasting antiamnesic effect of a novel anticholinesterase inhibitor (MF268)

In the present study a short (120 min) and long-lasting (360 min) antagonism of scopolamine-induced amnesia in rats was investigated in an eight-arm radial maze, by (3a S, 8a R)-1,2,3,3a,8,8a-hexahydro-1,3a,8-trimethylpyrrolo[2,3-b]indol-5-o l[8-(cis2,6-dimethyl-morpholin-4-yl)octyl]-carbamate L-bitartrate hydrate (MF268), a new cholinesterase inhibitor. Upon completing the training session, the rats were orally administered increasing doses of MF268 (2, 3, 6, 7, and 8 mg/kg) 60 min prior to s.c. injection of scopolamine (0.25 mg/kg). Following a further 60 min the rat was placed in the maze. The reversal of scopolamine-induced impairment was characterized by an inverted U-shaped dose-response curve. A significant reduction in the number of errors, and time taken to complete the maze was observed with a dose of 6 mg/kg. The compound improved memory retention without affecting scopolamine-induced hypermotility. When the same dose was administered 360 min prior to the test a significant reduction in the number of amnesic animals was observed, whereas no cognitive improvement was detected when either 1-Benzil-4-[(5,6-dimethoxy-1-indanon)-2-yl]-methyl piperidine hydrochloride (E2020) (0.25 mg/kg) or tacrine (0.5 mg/kg) were administered 360 min prior to the test. The kinetics of whole-brain cholinesterase confirmed the long-lasting activity for MF268. A clinical relevance for the use of MF268 in AD treatment is suggested.

Relationship between pharmacodynamic activity and cognitive effects of eptastigmine in patients with Alzheimer's disease. Eptastigmine Study Group

OBJECTIVE

To assess the safety, tolerability, pharmacodynamics, and preliminary efficacy of eptastigmine, a new long-acting cholinesterase inhibitor, in patients with probable Alzheimer's disease.

METHODS

This was a double-blind, randomized, placebo-controlled, unbalanced parallel-group study. One-hundred and three patients (83 in the eptastigmine group and 20 in the placebo group) were recruited by 10 centers. Patients received 20 mg eptastigmine or placebo for 4 weeks with twice-a-day or three-times-a-day regimens, depending on body weight (< or = 65 kg or > 65 kg, respectively). Patient performance on the Logical Memory Test, Semantic Word Fluency Test, Trail Making Test, Index of Independence in Activities of Daily Living, Instrumental Activities of Daily Living Scales (IADL), and the Physician and Caregiver Clinical Global Impression of Change (CGIC) was assessed at baseline and at the end of treatment.

RESULTS

Nine patients, all from the eptastigmine group, did not complete treatment because of uncooperativeness (n = 3), adverse events (n = 3), protocol violations (n = 2), and clinical decline (n = 1). Twenty-five patients receiving eptastigmine (34%) reported adverse events mainly of the cholinergic type. Cholinergic side effects were generally associated with peak red blood cell cholinesterase inhibition exceeding 50% after the first dose, or 70% at steady state. At steady state, average daily acetylcholinesterase inhibition ranged from 13% to 54%. Overall, 34% of patients receiving eptastigmine versus 0% receiving placebo (p = 0.006) improved on the Physician CGIC. This percentage increased to 46% in the subgroup of patients with average daily acetylcholinesterase inhibition ranging from 30% to 35%. Patient performance on the IADL also improved significantly compared with the placebo group (p = 0.019). In the eptastigmine group, performances on all tests and scales improved with an inverted U-shaped relation to average daily acetylcholinesterase inhibition.

CONCLUSIONS

This study shows that doses of 40 to 60 mg per day of eptastigmine are relatively safe and well tolerated and that moderate acetylcholinesterase inhibition is associated with maximal cognitive efficacy.

Relationship between pharmacokinetics and pharmacodynamics of eptastigmine in young healthy volunteers

Eptastigmine is a long-lasting acetyl-cholinesterase inhibitor, currently being developed for the symptomatic treatment of Alzheimer's disease. In the present study, we investigated the relationship between pharmacokinetics and pharmacodynamics of eptastigmine in young healthy volunteers. Eight male subjects received single oral doses of 10, 20, and 30 mg of eptastigmine and placebo according to a double-blind, randomized, crossover design. Blood was collected before and 0.5, 1, 1.5, 2, 3, 4, 6, and 24 hours after drug administration. Cholinesterase activity was measured using a potentiometric method in both plasma (butyryl-cholinesterase) and in red blood cells (acetyl-cholinesterase). Eptastigmine plasma levels were measured by a very sensitive high-performance liquid chromatography method (limit of quantitation 0.2 ng/mL). Eptastigmine plasma concentrations increased proportionally with the dose (mean +/- SEM AUC0-24 was 0.74 +/- 0.58, 3.61 +/- 1.15, and 6.25 +/- 1.51 ng.h/mL with 10, 20, and 30 mg, respectively) and were undetectable at 24 hours. The inhibition of acetyl-cholinesterase was dose-dependent (peak inhibition was 15 +/- 2%, 30 +/- 4%, and 36 +/- 6% with 10, 20, and 30 mg, respectively) and long-lasting, with a residual inhibition of 8 to 11% at 24 hours. Acetyl-cholinesterase inhibition and drug plasma levels were related over time with a counterclockwise hysteresis curve, suggesting the formation of active metabolites and/or a slow association to and dissociation from the enzyme in red blood cells. Butyryl-cholinesterase inhibition was weak and not dose-dependent (peak inhibition was 12 +/- 4%, 13 +/- 3%, and 12 +/- 2% with 10, 20, and 30 mg, respectively). The drug was well tolerated by all subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid potentiometric determination of cholinesterases in plasma and red cells: application to eptastigmine monitoring

Eptastigmine (MF 201) is a new physostigmine derivative with potent inhibitory activity on cholinesterases. Here we present a new potentiometric cholinesterase activity assay suitable for MF 201 monitoring. The analysis is performed on a differential pH system and has the following characteristics: (a) within-run precision: C.V. 2.0% (plasma cholinesterase), 1.8% (red cell cholinesterase); (b) between-run precision: C.V. 4.0% (plasma cholinesterase); (c) linearity: 1-10 kU/l (plasma cholinesterase), 6-70 U/g Hb (red cell cholinesterase); (d) comparison with a reference method (x, HITACHI 737 Boerhinger Mannheim, Italy): y = 0.785x - 0.07; n = 37; r = 0.998. The assay has been applied to the determination of plasma and red cell cholinesterase activity in volunteers over 60 years of age treated with a single oral dose of 30 mg eptastigmine. We found that red cell cholinesterase is selectively inhibited after MF 201 administration with the following kinetics (time, % of inhibition, mean +/- S.E., n = 6): 0 h, 0; 1 h, 17 +/- 4.6; 2 h, 24 +/- 4; 4 h, 23 +/- 4.4; 12 h, 14 +/- 3. Eptastigmine plasma levels were also determined by a HPLC method: maximum concentration was found one hour after drug administration.

Determination of heptylphysostigmine in plasma by high-performance liquid chromatography with electrochemical detection

Heptylphysostigmine is a new and very promising cholinergic drug for the treatment of Alzheimer disease. A method has been developed for its determination in plasma with a detection limit of 50 pg/ml. The drug was extracted in n-hexane by a simple one-step procedure, after buffering with sodium bicarbonate. Samples were analysed on a 25 cm x 4.6 mm I.D. silica column (5 microns particle size) using a mixture of acetonitrile, methanol and ammonium nitrate as mobile phase. Since this molecule is quite unstable in plasma, pyridostigmine bromide was added to samples to limit the decomposition. Physostigmine was employed as internal standard. The molecule was electrochemically detected by oxidizing potential (+0.75 V). The method was applied to the analysis of blood samples taken from one healthy volunteer administered this drug. In the same subject the inhibition rate of acetylcholinesterase in plasma and red cells was also measured.

Eptastigmine augments basal and GHRH-stimulated growth hormone release in young and old dogs

The aim of the present work was to evaluate the effect on the growth hormone (GH) secretion of eptastigmine, a new long-acting cholinesterase inhibitor, in unanesthetized beagle dogs. In a first study, 5 young dogs were given single doses (0.5, 1.0, and 2.0 mg/kg, i.m.) of the drug or saline in a randomized cross-over manner. Blood samples were collected immediately before and, at regular intervals, until 150 min after drug injection. GH plasma concentrations were determined by radioimmunoassay. Plasma cholinesterase activity was measured with a potentiometric method. There was a significant logistic relationship (r = 0.601, P < 0.01) between the administered dose of eptastigmine and the log-transformed areas under the GH plasma concentration-time curve (AUC) with a calculated ED50 for eptastigmine of 0.63 +/- 0.36 mg/kg. There was also a significant linear relationship (r = 0.630, P < 0.01) between log-transformed AUC of GH levels and AUC of plasma cholinesterase activity. In a second study we evaluate the ability of eptastigmine (2.0 mg/kg, i.m.) to potentiate the GH-releasing effect of the GH-releasing hormone (GHRH, 2.0 micrograms/kg, i.v.) in young and old dogs. Eptastigmine was administered 45 min before GHRH and blood collected every 15 min until 90 min after GHRH injection. In young dogs, maximum GH plasma levels (Cmax) were 6.1 +/- 1.0 ng/ml after GHRH compared to 22.5 +/- 2.3 ng/ml after GHRH preceded by eptastigmine (P < 0.01). In old animals, Cmax were 4.6 +/- 1.4 ng/ml after GHRH vs 13.2 +/- 7.4 ng/ml after combined administration of GHRH and eptastigmine (P < 0.05). These data indicate that eptastigmine is very effective in augmenting basal and stimulated GH secretion in old dog. The good activity also shown in old animals suggests a potential use of this drug to reverse the age-dependent decline in GH secretion responsible for many involutional changes of aging.

A semiautomated flow injection procedure for acetylcholinesterase and cholinesterase activities

A stopped-flow FIA adaptation of the classical Ellman's colorimetric procedure for the measurement of acetylcholinesterase or cholinesterase activity is described. The samples are injected into a flow analytical system which is provided with an electronic timer and an electrovalve in order to stop the flow when the sample is inside the measurement cell. In this way, the absorbance-time relationship is obtained with a savings of sample, time, and reagents.

Whole blood L-lactate assay by a new differential pH method: application to metabolic investigations

We propose a new quantitative method for L-lactate assay in whole blood, based on the measurement of pH variation caused by specific and irreversible oxidation of L-lactate to pyruvate in the presence of an electron acceptor (hexacyanoferrate) and of the enzyme cytochrome b2 (EC 1.1.2.3.). No sample pretreatment is needed; the method is simple and fast (1.5 min/analysis) and requires 10 microliters whole blood per assay. Linearity is confirmed up to 20 mmol/l L-lactate. Within-day and between-day variability was (as C.V.) 3.6% and 8.1% for blood lactate 1.3 and 1.0 mmol/l, respectively. The results by the present method correlate well with those from two reference methods (test method vs a lactate sensor based method: r = 0.996; test method vs a spectrophotometric method: r = 0.987). An application of the present method to the continuous monitoring of L-lactate in patients after combined kidney and pancreas transplantation, under conditions of euglycemic hyperinsulinemia and hyperglycemic hyperinsulinemia is reported. We conclude that the method is simple and reproducible and can be employed to measure whole blood lactate concentration continuously both in clinical protocols and in basic research.

Determination of serum cholinesterase activity and dibucaine numbers by an amperometric choline sensor

Serum cholinesterase activity and the dibucaine numbers have been determined by using a hydrogen peroxide electrode and the enzyme choline oxidase immobilized on a nylon net. The analysis procedure is extremely simple and very fast allowing 30 cholinesterase determinations per hour. Both cholinesterase activity and dibucaine number measurements could be performed in 5 min and by using serum samples of only 10 microliters. When used in sera the probe showed no interference from electroactive compounds present in blood, and also showed good stability and reproducibility. These features make this sensor appropriate for continuous extracorporeal circuit blood monitoring of succinylcholine during surgery.