A modification of the kinetic determination of pancuronium bromide based on its inhibitory effect on cholinesterase

A modification of the existing spectrophotometric kinetic method for the determination of pancuronium bromide (PCBr), based on pooled human serum cholinesterase (ChE, EC 3.1.1.8 acylcholine acylhydrolase) inhibition, was developed. Butyrylthiocholine iodide (concentration 1.667 mmol/L) was used as substrate and determination was performed at pH 7.6. Essential basic kinetic parameters were also determined: Michaelis-Menten's constant KM=0.33 mmol/L, maximal reaction rate Vmax=42.29 micromol/L min, inhibition constant KI=0.34 micromol/L, and IC50=0.235 micromol/L. Linear dependence between the reaction rate and the inhibitor concentration exists in PCBr concentration range 8.29-265.28 nmol/L, which corresponds to the real sample concentrations from 0.166 to 5.306 micromol/L. The method detection limit was established to be 1.86 nmol/L and the quantification limit was 6.18 nmol/L. Precision of the method was tested for three pancuronium concentrations (16.58, 99.48, and 198.96 nmol/L). The relative standard deviation (RSD) was in the range 0.78-5.13%. Accuracy was examined by the standard addition method. The influence of substances usually present in serum and urine on the reaction rate was determined. The method developed was applied for PCBr determination in spiked serum and urine samples and in the urine taken during surgery. The method was proven to have good sensitivity, accuracy, and precision and can be considered suitable for clinical practice.

Insecticide detection through protein engineering of Nippostrongylus brasiliensis acetylcholinesterase B

The sensitivity of acetylcholinesterase (AChE) biosensors for insecticide detection could be increased substantially by engineering AChE B of Nippostrongylus brasiliensis. The introduction of 10 single and 4 double mutations into the AChE peptide chain led to an increase in sensitivity to 10 of the 11 insecticides tested. The combination of three mutants with the wild-type enzyme in a multienzyme biosensor array enabled the detection of 11 out of the 14 most important organophosphates and carbamates at concentrations below 10 microg/kg, the maximum residue limit of infant food. The detection limit for pirimiphos methyl could be reduced from 10 microg/L to a value as low as 1 ng/L (3.5 x 10(-)(12) mol/L). The newly created biosensors exhibited an extraordinary high storage stability. There was no loss of sensitivity of N. brasiliensis AChE B, immobilized on screen-printed, disposable electrodes, even after 17-month storage at room temperature.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay for organophosphorus toxicants bound to human albumin at Tyr411

Our goal was to determine whether chlorpyrifos oxon, dichlorvos, diisopropylfluorophosphate (DFP), and sarin covalently bind to human albumin. Human albumin or plasma was treated with organophosphorus (OP) agent at alkaline pH, digested with pepsin at pH 2.3, and analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Two singly charged peaks m/z 1718 and 1831, corresponding to the unlabeled peptide fragments containing the active site Tyr411 residue, were detected in all samples. The sequences of the two peptides were VRYTKKVPQVSTPTL and LVRYTKKVPQVSTPTL. The peptide-OP adducts of these peptides were also found. They had masses of 1854 and 1967 for chlorpyrifos oxon, 1825 and 1938 for dichlorvos, 1881 and 1994 for DFP, and 1838 and 1938 for sarin; these masses fit a mechanism whereby OP bound covalently to Tyr411. The binding of DFP to Tyr411 of human albumin was confirmed by electrospray tandem mass spectrometry and analysis of product ions. None of the OP-albumin adducts lost an alkoxy group, leading to the conclusion that aging did not occur. Our results show that OP pesticides and nerve agents bind covalently to human albumin at Tyr411. The presence of Tyr411 on an exposed surface of albumin suggests that an antibody response could be generated against OP-albumin adducts.

Acute toxicity and acetylcholinesterase inhibition in grass shrimp (Palaemonetes pugio) and oysters (Crassostrea virginica) exposed to the organophosphate dichlorvos: laboratory and field studies

The use of various organophosphates to control mosquito populations is a common practice across the globe. We review the literature (LC50s) on dichlorvos, the primary breakdown product of Dibrom, and use laboratory and field experiments to determine the lethal and sublethal (bioassays) effects of dichlorvos on two widely distributed and ecologically important estuarine invertebrate species, the marsh grass shrimp, Palaemonetes pugio and the Eastern oyster, Crassostrea virginica. Laboratory results based on LC50s and sublethal acetylcholinesterase (AChE) inhibition activity bioassays indicate that adult grass shrimp are more sensitive (approximately 500 x ) to dichlorvos than juvenile oysters. Although potentially an important factor for intertidal or shallow-dwelling estuarine organisms, the toxicity of dichlorvos was not enhanced in the presence of simulated sunlight for adult P. pugio. The most notable decreases in AChE activity were for grass shrimp and oysters exposed to dichlorvos concentrations above those considered ecologically relevant. In field experiments, both species were deployed in cages in unsprayed (n = 2) and sprayed (n = 3) sites and water samples collected pre- and post-spraying. Quantifiable dichlorvos levels were measured at the two narrowest creek treatment sites following mosquito spraying, suggesting that overspray can occur and there was evidence of a sublethal AChE response at these same sites. However, experiments at the widest creek revealed no measurable dichlorvos or sublethal responses. Results from this research suggest that adult grass shrimp are more sensitive to dichlorvos than juvenile oysters. Spraying near small tidal creeks may have measurable impacts on resident species, while larger (wider) creeks appear to be capable of buffering organisms from transient fluxes of mosquito control agents that may enter the system.

Screening of acetylcholinesterase inhibitors in natural extracts by CE with electrophoretically mediated microanalysis technique

An electrophoretically mediated microanalysis (EMMA) method for screening acetylcholinesterase (AChE) inhibitors in natural extracts is described. In this method, solutions of AChE and the mixture of the substrate and the natural extract were successively injected into the capillary, and mixed electrophoretically by applying a voltage for a short time. Afterwards the voltage was reapplied to separate the product from the unreacted substrate and the natural extract. The measured peak area of the product at UV 230 nm represents the enzyme activity. Since the extract is mixed with the substrate, there is no need to separate the components before testing the inhibition. The inhibitory activity of the natural extract as a whole can be easily found if the peak area of the product is reduced. This makes the present method suitable for screening inhibitors in complex mixtures, such as natural extracts. Compared to the commonly used spectrometric method for screening of AChE inhibitors, the major advantage of the present method is the elimination of Ellman reagent, which is essential for the spectrometric method. This not only simplifies the experimental procedure but also minimizes false-positive results. Moreover, it is an obvious advantage of combining the separation power with the on-column enzyme assay for further investigating which compound(s) is/are responsible for the inhibition. The method was validated using a commercially available AChE inhibitor tacrine and a small chemical library containing four AChE inhibitors and 32 natural extracts. Inhibitors in natural extracts were identified with the present method.

Doñana National Park survey using crayfish (Procambarus clarkii) as bioindicator: Esterase inhibition and pollutant levels

Utility of carboxylesterase and acetylcholinesterase inhibition as pesticide exposure biomarker was studied at Doñana National Park (SW Spain) in crayfish (Procambarus clarkii). Activities were measured in animals from reference sites or potentially exposed to pesticides, and their reactivation studied after dilution or 2-PAM treatment. Crayfish from affected sites had significantly less carboxylesterase and acetylcholinesterase activity than reference ones. No significant differences were found after dilution or 2-PAM treatment, showing that inhibition was irreversible. High pesticide levels were found in water and/or soil at rice growing sites, and lower levels at other affected places. High metal levels existed at rice growing sites and lower at other affected and at both reference sites. A combined effect on esterase inhibition of pesticides and metals is proposed. This field study suggest that the rice growing areas near Guadiamar stream are most polluted, followed by strawberry and citrics growing zones near Partido and Rocina streams. However, no correlation exist between the pesticide concentration at different sites and the extent of esterase inhibition, indicating that other factors could affect esterase response of animals from polluted sites.

Photodegradation of organophosphorus insecticides - investigations of products and their toxicity using gas chromatography-mass spectrometry and AChE-thermal lens spectrometric bioassay

Four organophosphorus compounds: azinphos-methyl, chlorpyrifos, malathion and malaoxon in aqueous solution were degraded by using a 125 W xenon parabolic lamp. Gas chromatography-mass spectrometry (GC-MS) was used to monitor the disappearance of starting compounds and formation of degradation products as a function of time. AChE-thermal lens spectrometric bioassay was employed to assess the toxicity of photoproducts. The photodegradation kinetics can be described by a first-order degradation curve C=C0e(-kt), resulting in the following half lives: 2.5min for azinphos-methyl, 11.6 min for malathion, 13.3 min for chlorpyrifos and 45.5 min for malaoxon, under given experimental conditions. During the photoprocess several intermediates were identified by GC-MS suggesting the pathway of OP degradation. The oxidation of chlorpyrifos results in the formation of chlorpyrifos-oxon as the main identified photoproduct. In case of malathion and azinphos-methyl the corresponding oxon analogues were not detected. The formation of diethyl (dimethoxy-phosphoryl) succinate in traces was observed during photodegradation of malaoxon and malathion. Several other photoproducts including trimethyl phosphate esters, which are known to be AChE inhibitors and 1,2,3-benzotriazin-4(3H)-one as a member of triazine compounds were identified in photodegraded samples of malathion, malaoxon, and azinphos-methyl. Based on this, two main degradation pathways can be proposed, both result of the (P-S-C) bond cleavage taking place at the side of leaving group. The enhanced inhibition of AChE observed with the TLS bioassay during the initial 30 min of photodegradation in case of all four OPs, confirmed the formation of toxic intermediates. With the continuation of irradiation, the AChE inhibition decreased, indicating that the formed toxic compounds were further degraded to AChE non-inhibiting products. The presented results demonstrate the importance of toxicity monitoring during the degradation of OPs in processes of waste water remediation, before releasing it into the environment.

Screening of Indian medicinal plants for acetylcholinesterase inhibitory activity

The cholinergic hypothesis of Alzheimer's disease (AD) has provided the rationale for the current pharmaco-therapy of this disease, in an attempt to reduce the cognitive decline caused by cholinergic deficits. Nevertheless, the search for potent and long-acting acetylcholinesterase (AChE) inhibitors that exert minimal side effects in AD patients is still ongoing. AChE inhibitors are currently the only approved therapy for the treatment of Alzheimer's disease; only a limited number of drugs are commercially available. Hydroalcohol extracts of six herbs, Andrographis paniculata, Centella asiatica, Evalvulus alsinoides, Nardostachys jatamansi, Nelumbo nucifera, Myristica fragrans used in Indian systems of medicine, were tested for in vitro acetylcholinesterase inhibitory activity based on Ellman's method in 96-well microplates using AChE obtained from bovine erythrocytes. The results showed that the hydroalcohol extract from Centella asiatica, Nardostachys jatamansi, Myristica fragrans, Evalvulus alsinoides inhibited 50% of AChE activity at concentrations of 100-150 microg/mL. Andrographis paniculata and Nelumbo nucifera extracts showed a weak inhibition of acetylcholinesterase with IC(50) values of 222.41 +/- 19.87 microg/mL and 185.55 +/- 21.24 microg/mL, respectively. Physostigmine was used as a standard and showed inhibition of acetylcholinesterase with an IC(50) value of 0.076 +/- 0.0042 microg/mL.

Impact of chemical exposure on the fish Pomatoschistus microps Krøyer (1838) in estuaries of the Portuguese Northwest coast

Juveniles of the estuarine fish Pomatoschistus microps were collected from autumn 2001 to summer 2002 in five stations along the Portuguese Northwest coast with different types and/or levels of environmental contamination: two reference sites with low levels of contamination (R1 and R2) and three differently impacted areas with higher levels of contamination. UI is located in an estuary under the influence of urban and industrial effluents, AA in a channel that receives intensive agriculture run-off and IE in a highly impacted industrial area. The activity of the enzymes acetylcholinesterase (AChE), lactate dehydrogenase (LDH), 7-ethoxyresorufin O-deethylase (EROD) and glutathione S-transferases (GST) were used as environmental biomarkers on P. microps. A significant seasonality effect on all the enzymatic activities was found, lower levels being registered in winter and spring on AChE, in autumn on LDH, and in winter on GST and EROD. The battery of biomarkers used was capable of discriminating sites with different types and/or levels of contamination, R1 and UI being the highest discriminated (91.7% and 66.7%, respectively). At R1 significantly lower levels of AChE and LDH were found, and EROD was significantly inducted at UI. Furthermore, IE presented higher levels of GST, and R2 and AA an inhibition of AChE in winter and spring. The results indicated that the battery of biomarkers used in this study seems to be a useful tool to distinguish between different types of environmental contamination in estuarine systems, and that P. microps is a suitable species to be used as bioindicator.

Flow-injection determination of carbaryl and carbofuran based on KMnO4–Na2SO3 chemiluminescence detection

A flow-injection method is described for the determination of carbaryl and carbofuran. It was found that a strong chemiluminescence (CL) signal was generated when these pesticides were mixed with Na(2)SO(3) and KMnO(4) in acidic medium. Under the optimum experimental conditions, the enhanced CL intensity was linear, with the concentrations in the range 0.1-2.0 microg/mL (r(2) = 0.9996 and 0.9993, n = 6) with relative standard deviation (n = 4) in the range 1.0-2.3%. The limits of detection (3sigma blank) were 10 and 50 ng/mL, respectively, with a sample throughput of 180/h. The proposed method was applied to determine carbaryl and carbofuran in freshwaters with satisfactory results. Most metal and non-metal ions and some pesticides, such as carbophenothion and aldicarb, do not interfere with the determination. Dinoseb, diazinon and malathion calibration graphs (in the range 0.2-2.0 microg/mL, r(2) = 0.9966-0.9988, n = 6) were also established with relative standard deviations (n = 4) in the range 1.2-2.0% with limits of detection (3sigma blank) in the range 100-300 ng/mL.

Production of a novel recombinant Drosophila melanogaster acetylcholinesterase for detection of organophosphate and carbamate insecticide residues

A novel recombinant Drosophila melanogaster acetylcholinesterase (R-DmAChE) produced in Pichia pastoris was first reported in this study. We cloned the DmAChE cDNA by reverse transcription PCR with removal of the signal for glycosylphosphatidylinositol (GPI) anchor attachment and the endogenous signal peptide coding sequence, and inserted it into P. pastoris vector pPIC9K under control of the alcohol oxidase gene AOX1 promoter (5'AOX1). The expression cassette of AChE cDNA was then introduced into methylotrophic yeast GS115 and several recombinant strains expressing R-DmAChE were obtained. The secreted R-DmAChE showed high stability in neutral phosphate buffer at 4 degrees C, and its kinetic parameters were identical to those of the native DmAChE. The bimolecular rate constants of R-DmAChE to dichlorvos, aldicarb and carbaryl were ranging from three to six times higher than of native DmAChE. Within six insecticides, the R-DmAChE was more sensitive than EeAChE, NbAChE and HuAChE. For 10 widely used insecticides, the IC50 values to the R-DmAChE were much lower than those to AChEs commonly used in China. With the R-DmAChE-based assay, samples spiked with three concentrations of pesticides caused enzymatic activity inhibition with R.S.D. of 0-13.7%. These results suggest that the R-DmAChE can be useful for detection of organophosphate and carbamate insecticide residues.

Acetylcholinesterase–ISFET based system for the detection of acetylcholine and acetylcholinesterase inhibitors

A bioelectronic hybrid system for the detection of acetylcholine esterase (AChE) catalytic activity was assembled by way of immobilizing the enzyme to the gate surface of an ion-sensitive field-effect transistor (ISFET). Photometric methods used to characterize bonded enzyme and linker layers on silicon substrates confirm the existence of a stable amino-cyanurate containing AChE monolayer. The transduction of the enzyme-functionalized ISFET, in ionic solutions, is detected in response to application of acetylcholine (ACh). Recorded sensitivity of the modified ISFET to ACh has reached levels of up to 10(-5)M. The Michaelis-Menten constant of the immobilized AChE is only moderately altered. Nevertheless, the maximum reaction velocity is reduced by over an order of magnitude. The ISFET response time to bath or ionophoretic application of ACh from a micropipette was in the range of a second. The catalytic activity of the immobilized AChE is inhibited in a reversible manner by eserine, a competitive inhibitor of AChE. We conclude that the immobilized enzyme maintains its pharmacological properties, and thus the described bioelectronic hybrid can serve as a detector for reagents that inhibit AChE activity.

Characterization of reversible and pseudo-irreversible acetylcholinesterase inhibitors by means of an immobilized enzyme reactor

The aim of the present study was the application of a human AChE-CIM-IMER (enzyme reactor containing acetylcholinesterase immobilized on a monolithic disk) for the rapid evaluation of the thermodynamic and kinetic constants, and the mechanism of action of new selected inhibitors. For this application, human recombinant AChE was covalently immobilized onto an ethylenediamine (EDA) monolithic Convective Interaction Media (CIM) disk and on-line studies were performed by inserting this IMER into a HPLC system. Short analysis time, absence of backpressure, low nonspecific matrix interactions and immediate recovery of enzyme activity were the best characteristics of this AChE-CIM-IMER. Mechanisms of action of selected reversible inhibitors (tacrine, donepezil, edrophonium, ambenonium) were evaluated by means of Lineweaver-Burk plot analysis. Analyses were performed on-line by injecting increasing concentrations of the tested inhibitor and substrate and by monitoring the product peak area. AChE-CIM-IMER kinetic parameters (Km(app) and vmax(app)) were derived as well as inhibitory constants (Ki(app)) of selected compounds. Moreover, noteworthy results were obtained in the application of the AChE-CIM-IMER to the characterization of the carbamoylation and decarbamoylation steps in pseudo-irreversible binding of carbamate derivatives (physostigmine and rivastigmine). AChE-CIM-IMER appeared to be a valid tool to determine simultaneously the kinetic constants in a reliable and fast mode. The obtained values were found in agreement with those obtained with the classical methods with the free enzyme. Furthermore, after inactivation by carbamates, activity could be fully recovered and the AChE-CIM-IMER could be reused for further studies. Results showed that the AChE-CIM-IMER is a valid tool not only for automated fast screening in the first phase of the drug discovery process but also for the finest characterization of the mode of action of new hit compounds with increased accuracy and reproducibility and with saving of time and materials.

Acetylcholinesterase: converting a vulnerable target to a template for antidotes and detection of inhibitor exposure

Applications of recombinant DNA technology, chemical synthesis on biological templates and fluorescence detection of organophosphorylation provide unexplored avenues for development of antidotes and approaches for remote detection of organophosphate nerve agents and pesticides. We discuss here how acetylcholinesterase (AChE), through appropriate mutations, becomes more susceptible to oxime reactivation. Since the reaction between organophosphate and the mutated enzyme remains rapid, regeneration of active enzyme by oxime becomes the rate-limiting step in the process to complete a catalytic cycle for generation of active enzyme. Accordingly, "Oxime-assisted Catalysis" by AChE provides a potential means for catalyzing the hydrolysis of organophosphates in plasma prior to their reaching the cellular target site. In turn, AChE, when conjugated with organophosphate, is employed as a template for 'click-chemistry, freeze-frame' synthesis of new nucleophilic reactivating agents that could potentially prove useful in AChE reactivation at the target site as well as in catalytic scavenging of organophosphates in plasma. Finally, substituted AChE molecules can be conjugated to fluorophores giving rise to shifts in emission spectra for detection of dispersed organophosphates. Since external reagents do not have to be added to detect the fluorescence change, the modified enzyme would serve as a remote sensor.

Silica-immobilized enzyme reactors; application to cholinesterase-inhibition studies

A rapid and economical method is reported for the preparation of an immobilized enzyme reactor (IMER) using silica-encapsulated equine butyrylcholinesterase (BuChE) as a model system. Peptide-mediated silica formation was used to encapsulate BuChE, directly immobilizing the enzyme within a commercial pre-packed column. The silica/enzyme nanocomposites form and attach simultaneously to the metal affinity column via a histidine-tag on the silica-precipitating peptide. BuChE-IMER columns were integrated to a liquid chromatography system and used as a rapid and reproducible screening method for determining the potency of cholinesterase inhibitors. The IMER preparation method reported herein produces an inert silica-encapsulation matrix with advantages over alternative systems, including ease of preparation, high immobilization efficiency (70-100%) and complete retention of activity during continuous use.

Survey of carbamate and organophosphorous pesticide export from a south Florida (U.S.A.) agricultural watershed: implications of sampling frequency on ecological risk estimation

The objectives of the present study were to characterize the presence of selected carbamate and organophosphorous pesticides in Ten Mile Creek (Fort Pierce, FL, U.S.A.) and to evaluate the implications of sampling frequency on ecological risk estimates. Ten Mile Creek originates in a predominately agricultural watershed that is drained by an extensive network of cross-linked canals. Water samples were collected daily or every other day and were analyzed for azinphos-methyl, chlorpyrifos, diazinon, dimethoate, ethion, fenamiphos, malathion, methidathion, carbaryl, carbofuran, 3-hydroxycarbofuran, methiocarb, methomyl, oxamyl, and propoxur. A total of 457 samples were analyzed for the carbamate suite, and a total of 332 samples were analyzed for the organophosphorous suite. Carbaryl was detected in eight samples; half of these detections occurred on four consecutive days (October 26-29, 2001) at concentrations ranging from 0.33 to 0.95 microg/L. Methomyl was detected in samples collected on five consecutive days (March 30-April 3, 2002) at concentrations ranging from 1.0 to 2.2 microg/L. Oxamyl was detected in four samples, three of which occurred on three consecutive days (February 17-19, 2002) at concentrations ranging from 6.2 to 6.8 microg/L. The carbamates propoxur, 3-hydroxycarbofuran, carbofuran, and methiocarb were not detected. Diazinon and ethion were the only organophosphorous pesticides detected. Diazinon was detected at 0.9 and 0.7 microg/L on January 5, 2002, and on January 6, 2002, respectively. Ethion was detected in 18 consecutive samples (August 3-20, 2001). The mean, maximum, minimum, and median detected concentrations were 0.38, 0.61, 0.30, and 0.33 microg/L, respectively. Results indicate that frequent sampling is necessary to characterize the presence of these pesticides in this intensively drained watershed. This conclusion also may apply to similar canalized watersheds.

Monitoring enzyme reaction and screening enzyme inhibitor based on MALDI-TOF-MS platform with a matrix of oxidized carbon nanotubes

A matrix assisted laser desorption/ionization time-of-flight mass spectrometry platform for quantitatively monitoring enzyme activity and screening enzyme inhibitors has been demonstrated. The described method employs a new matrix of oxidized carbon nanotubes. Compared with the traditional fluorescence approach, this label-free method has the advantage of directly identifying the substrates and products in enzymatic reactions. Moreover, the method could be conveniently carried out with any commercial mass spectrometer without modification. We quantitatively monitored the acetylcholinesterase activity and screened acetylcholinesterase inhibitors with a detection rate of about 3.3 s per sample.

Rapid method for evaluation of cholinesterase inhibitors

The fluorescence intensity of reversible inhibitor ethidium bromide fluorophore complex with equine blood butyryl cholinesterase decreases in the presence of inhibitor (tacrine) not fluorescing in the visible spectrum. An express method for tacrine evaluation is developed.

[Study of the interaction of main potato glycoalkaloids in inhibition of immobilized butyryl cholinesterase]

The interaction of main potato glycoalkaloids alpha-solanine and alpha-chaconine in inhibition of horse serum butyryl cholinesterases immobilized on the pH-sensitive field-effect transistors has been investigated. The method of isobol diagram of Loewe and Muishnek has been used for interpretation of results. It has been shown the alpha-chaconine inhibits the immobilized bytyryl cholinesterases more strongly than alpha-solanine, and their mixture has the addition effect.

Changes in the activity and protein levels of CSF acetylcholinesterases in relation to cognitive function of patients with mild Alzheimer's disease following chronic donepezil treatment

OBJECTIVES

To evaluate long-term changes in acetylcholinesterase (AChE) activity in CSF and blood following donepezil treatment in relation to the concentration of donepezil and cognition in AD patients.

METHODS

CSF or blood (or both) samples of a total of 104 patients with mild AD were used [MMSE score 23 +/- 0.4; age 75 +/- 1 years (mean +/- SEM); n=53 for CSF and n=51 for plasma/red blood cell (RBC) samples]. The patients were treated with 5 or 10 mg/day donepezil and clinically followed for 2 years. The CSF and RBC AChE activities were measured by the Ellman's direct colorimetric assay. Protein levels of two variants of AChE ("read-through" AChE-R and synaptic AChE-S) were determined by an ELISA-like method.

RESULTS

The plasma donepezil concentration was dose-dependent (between 30 and 60 ng/mL in the 5-mg and 10-mg group, respectively). The CSF donepezil concentration was 10 times lower than the plasma level and showed dose- and time-dependent kinetics. The RBC AChE inhibition was moderate (19-29%). CSF AChE-S inhibition was estimated to 30-40% in the 5-mg and 45-55% in the 10-mg group. Positive correlations were observed between the CSF AChE inhibition, an increased protein level of the AChE-R variant and MMSE examination. Patients with high AChE inhibition (>or=45%) showed a stabilized MMSE test result after up to two years, while a significant decline was observed in AD patients with lower AChE inhibition (<or=30%).

CONCLUSIONS

An increase in the protein level of the AChE-R variant corresponded to a high AChE inhibition in CSF and favored less cognitive deterioration.

[Separation and determination of donepezil hydrochloride enantiomers in plasma by capillary electrophoresis]

AIM

To establish chiral separation method for donepezil hydrochloride (E2020) enantiomers by capillary electrophoresis (CE) and determine the two enantiomers in plasma.

METHODS

Alkalized plasma was extracted by isopropanol-n-hexane (3 : 97) and L-butefeina was used as the internal standard. Enantioresolution was achieved using 2.5% sulfated-beta-cyclodextrin as chiral selector in 25 mmol x L(-1) triethylammonium phosphate solution (pH 2.5) on the uncoated fused-silica capillary column (70 cm x 50 microm ID). The feasibility of the method to be used as quantitation of E2020 enantiomers in rabbit plasma was also investigated.

RESULTS

E2020 enantiomers were separated at a baseline level under the above condition. The linearity of the response was evaluated in the concentration range from 0.1 to 5 mg x L(-1). The linear regression analysis obtained by plotting the peak area ratio (A(s)/A(i)) of the analyte to the internal standard versus the concentration (C) showed excellent correlation coefficient (r = 0.999 2 for R(-)-E2020, r = 0.999 7 for S(+)-E2020) and the equations were A(s)/A(i) = 0.024 2 + 0.289 2C and A(s)/A(i) = 0.010 8 + 0.273 7C, respectively. The low limit of detection was 0.05 mg x L(_1). The inter- and intra-day precision (RSD) were all less than 20% .

CONCLUSION

Compared with CSP by HPLC, the CE method is simple, reliable, inexpensive and suitable for studying the stereoseletive pharmacokinetics in rabbits.

Determination of donepezil hydrochloride in human and rat plasma, blood and brain microdialysates by HPLC with a short C30 column

A simple and sensitive HPLC method with fluorescence (FL) detection for determination of donepezil (DP) in plasma and microdialysate samples was developed. A rapid isocratic separation of DP could be achieved by a short C30 column using mobile phases of 25 mM citric acid/50 mM Na2HPO4 (pH 6.0)-CH3CN (73:27%, v/v) containing 3.5 mM sodium 1-octanesulfonate for plasma and H2O-CH3CN-CH3OH (80:17:3%, v/v/v) containing 0.01% acetic acid for microdialysate. The eluate was monitored at 390 nm with an excitation at 325 nm. The detection limits (S/N = 3) of DP for human plasma, rat plasma and rat brain or blood microdialysates were 0.2, 1.0 and 2.1 ng/ml, respectively. Reproducible results could be obtained by using (+/-)-2-[(1-benzyl-piperidine-4-yl)ethyl]-5,6-dimethoxyindan-1-one hydrochloride as an internal standard (IS). The method was successfully applied for monitoring of DP levels in rat plasma, blood and brain microdialysates and patient plasma.

Fluorescent Sensors for Organophosphorus Nerve Agent Mimics

We present a small molecule sensor that provides an optical response to the presence of an organophosphorus (OP)-containing nerve agent mimic. The design contains three key features: a primary alcohol, a tertiary amine in close proximity to the alcohol, and a fluorescent group used as the optical readout. In the sensor's rest state, the lone pair of electrons of the basic amine quenches the fluorescence of the nearby fluorophore through photoinduced electron transfer (PET). Exposure to an OP nerve agent mimic triggers phosphorylation of the primary alcohol followed rapidly by an intramolecular substitution reaction as the amine displaces the created phosphate. The quaternized ammonium salt produced by this cyclization reaction no longer possesses a lone pair of electrons, and a fluorescence readout is observed as the nonradiative PET quenching pathway of the fluorophore is shut down.

Cholinesterase inhibition and impacts on behavior of the Asian clam, Corbicula fluminea, after exposure to an organophosphate insecticide

This study assessed the effects of exposure to an insecticide formulation containing the organophosphate, chlorpyrifos on cholinesterase activity, siphoning and burrowing ability in the Asian clam, Corbicula fluminea. Clams were exposed to concentrations of the pesticide ranging from 0.05 to 50 mg/L (as chlorpyrifos) in a series of 96-h static bioassays. Those organisms exposed to pesticide concentrations at or above 3.13 mg/L avoided exposure through valve closure during the 96-h test period, with no resultant effects on cholinesterase activity or behavior. Similarly, no effect was observed at low-test concentrations ranging from 0.05 to 0.1 mg/L, even though clams actively siphoned in these treatments. Asian clams exposed to the mid-range of concentrations, 0.5-1.0 mg/L, experienced a significant reduction in cholinesterase activity and a reduced capacity to burrow into the substrate. While these data indicate that cholinesterase activity in C. fluminea could be used as a biomarker of organophosphorous pesticide exposure, valve closure can clearly influence exposure profiles and biomarker response.

Probabilistic assessment of the cumulative acute exposure to organophosphorus and carbamate insecticides in the Brazilian diet

In the present study, the cumulative exposure of 25 acetylcholinesterase (AChE) inhibiting pesticides through the consumption of nine fruits and vegetables by the Brazilian population was assessed. Food consumption data were obtained from a household budget survey conducted in all Brazilian states from July 2002 to June 2003. Residue data from 4001 samples were obtained from the Brazilian national monitoring program on pesticide residues. Relative potency factors (RPF) were calculated with methamidophos or acephate as index compounds (IC), using BMD(10) or NOAEL for AChE inhibition, mostly in rat brain, obtained from national and international pesticide evaluations. Monocrotophos and triazophos, in addition to aldicarb, had the highest calculated RPF in any scenario. The exposure to AChE inhibiting pesticides for the general population at P99.9, represented 33.6% of the ARfD as methamidophos and 70.2% ARfD as acephate. The exposure calculated as acephate could exceed the ARfD at the upper bound of the 95% confidence interval for this percentile. Exposure for children aged up to 6 years were, on average, 2.4 times higher than the exposure for the general population. Tomato represented about 67% of the total intake of AChE inhibiting pesticides. The highest calculated equivalent residues in tomato, which drove most of the estimated intakes at the high percentiles, were related to the illegal use of monocrotophos and triazophos in this crop.